NOAA Technical Report NMFS 85

March 1990

Marine Farming and Enhancement
Proceedings of the Fifteenth
U.S.-Japan Meeting on Aquaculture
Kyoto, Japan
October 22-23, 1986
Albert K. Sparks (editor)

U.S. Department of CommerceNOAA TECHNICAL REPORT NMFS
The major responsibilities of the National Marine Fisheries Service (NMFS) are to monitor and assess the abundance and geographic distribution of fishery resources, tounderstand and predict fluctuations in the quantity and distribution of these resources, and to establish levels for their optimum use. NMFS is also charged with the development
and implementation of policies for managing national fishing grounds, development and enforcement of domestic fisheries regulations, surveillance of foreign fishing off UnitedStates coastal waters, and the development and enforcement of international fishery agreements and policies.!NMFS also assists the fishing industry through marketing service
and economic analysis programs, and mortgage insurance and vessel construction subsidies. It collects, analyzes, and publishes statistics on various phases of the industry.
The NOAA Technical Report NMFS series was established in 1983 to replace two subcategories of the Technical Reports series: "Special Scientific Report-Fisheries" and"Circular." The series contains the following types of reports: Scientific investigations that document long-term continuing programs of NMFS; intensive scientific reports on
studies of restricted scope; papers on applied fishery problems; technical reports of general interesl intended, to aid conservation and management; reports that review in considerable detail and at a high technical level certain broad areas of research; and technical papers originating in economics studies and from management investigations. Since
this is a formal series, all submitted papers receive peer review and those accepted receive professional editing before publication.
Copies of NOAA Technical Reports NMFS are available free in limited numbers to governmental agencies, both Federal and State. They are also available in exchange forother scientific and technical publications in the marine sciences. Individual copies may be obtained from: U.S. Department of Commerce, National Technical Information Service,5285 Port Royal Road, Springfield, VA 22161. Although the contents have not been copyrighted and may be reprinted entirely, reference to source is appreciated.
48. Widow rockfish: Proceedings of a workshop. Tiburon, California, Cecember
11-12,1980, by William H. Lelll\IZ and Donald R. Gunderson (editors). January 1987,
57 p.
49. Reproduction, movements, and population dynamics of the southern kingfish,
Menticirrhus americanus, in the northwestern Gulf of Mexico, by Stephen M. Harding
and Mark E. Chittenden, Jr. March 1987, 21 p.
50. Preparation of acetate peels of valves from the ocean quahog, Arctica i"landica,
for age determinations, by John W. Ropes. March 1987, 5 p.
51. Status, biology, and ecology of fur seals: Proceedings of an international
workshop, Cambridge, England, 23-27 April 1984, by John P. Croxall and Roger
L. Gentry (editors). June 1987, 212 p.
52. Limited access alternatives for the Pacific groundfish fishery, by Daniel D.
Huppert (editor). May 1987,45 p.
53. Ecology of east Florida sea turtles: Proceedings of the Cape Canaveral, Florida,
sea turtle workshop, Miami, Florida, February 26-27, 1985, by Wayne N. Witzell(convener and editor). May 1987, 80 p.
54. Proximate and fatty acid composition of 40 southeastern U.S. finfish species,
by Janet A. Gooch, Malcolm B. Hale, Thomas Brown, Jr., James C. Bonnet, Cheryl
G. Brand, and Lloyd W. Reiger. June 1987, 23 p.
55. Proximate composition, energy, fatty acid, sodium, and cholesterol content of
finfish, shellfish, and their products, by Judith Krzynowek and Jenny Murphy. July
1987, 53 p.
56. Some aspects of the ecology of the leatherback turtle Dennochelys coriacea at
Laguna Jolova, Costa Rica, by Harold F. Hirth and Larry H. Ogren. July 1987, 14 p.
57. Food habits and dietary variability of pelagic nekton off Oregon and Wa ,hington,
1979-1984, by Richard D. Brodeur, Harriet V. Lorz, and William G. Pearcy. July
1987, 32 p.
58. Stock assessment of the Gulf menhaden, Brevoonia patronus, fishery, by Douglas
S. Vaughan. September 1987, 18 p.
59. Atlantic menhaden, Brevoortia tyrannus, purse seine fishery, 1972-84, with abrief discussion of age and size composition of the landings, by Joseph W. Smith,William R. Nicholson, Douglas S. Vaughan, Donnie L. Dudley, and Ethel A. Hall.
September 1987, 23 p.
60. Gulf mellhaden, Brevoonia patronus, purse seine fishery, 1974-85, with a brief
discussion of age and size composition of the landings, by Joseph W. Smith, Eldon
J. Levi, Douglas S. Vaughan, and Ethen A. Hall. December 1987, 8 p.
61. Manual ior starch gel electrophoresis: A method for the detection of genetic variation, by Paul B. Aebersold, Gary A. Winans, David J. Teel, George B. Milner, andFred M. Utter. December 1987, 19 p.
62. Fishery publication index, 1980-85; Technical memoradum index, 19'i2-85, byCynthia S. Martin, Shelley E. Arenas, Jacki A. Guffey, and Joni M. Packard.
Oecember 1987, 149 p.
63. Stock assessment of the Atlantic menhaden, Brevoortia tyrannus, fishery, by
Douglas S. Vaughan and Joseph W. Smith. January 1988, 18 p.

64. illustrated key to penaeoid shrimps of commerce in the Americas, by Isabel Perez
Farfante. April 1988, 32 p.
65. History of whaling in and near North Carolina, by Randall R. Reeves and Edward
Mitchell. March 1988, 28 p.
66. Atlas and zoogeography of common fishes in the Bering Sea and northeastern
Pacific. by M. James Allen and Gary B. Smith. April 1988, 151 p.
67. Index numbers and productivity measurement in multispecies fisheries: An
application to the Pacific coast trawl fleet, by Dale Squires. July 1988, 34 p.
68. Annotated bibliography II of the hard clam Mercenaria mercenaria, by J.L.
McHugh and Marjorie W. Sumner. September 1988, 59 p.
69. Environmental quality and aquaculture systems: Proceedings of the thirteenth
U.S.-Japan meeting on aquaculture, Mie, Japan, October 24-25, 1984, edited by Carl
J. Sindermann. October 1988, 50 p.
70. New and innovative advances in biology/engineering with potential for use inaquaculture: Proceedings of the fourteenth U.S.-Japan meeting on aquaculture, Woods
Hole, Massachusetts, October 16-17. 1985, edited by Albert K. Sparks. November
1988, 69 p.
71 . Greenland turbot Reinhardtius hippoglossoides of the eastern Bering Sea andAleutian Islands region, by Miles S. Alton, Richard G. Bakkala, Gary E. Walters,
and Peter T. Munro. December 1988, 31 p.
72. Age determination methods for northwest Atlantic species, edited by Judy Penttila
and Louise M. Dery. December 1988, 135 p.
73. Marine flora and fauna of the Eastern United States. Mollusca: Cephalopoda,by Michael Vecchione, Clyde F.E. Roper, and Michael J. Sweeney. February 1989,
23 p.
74. Proximate composition and fatty acid and cholesterol content of 22 species ofnorthwest Atlantic finfish, by Judith Krzynowek, Jenny Murphy, Richard S. Maney,
and Laurie J. Panunzio. May 1989, 35 p.
75. Codend selection of winter flounder Pseudopleuronectes americanus, by David
G. Simpson. March 1989, 10 p.
76. Analysis of fish diversion efficiency and survivorship in the fish return system
at San Onofre Nuclear Generating Station, by Milton S. Love, Meenu Sandhu,
Jeffrey Stein, Kevin T. Herbinson, Robert H. Moore, Michael Mullin, and John S.
Stephens, Jr. April 1989, 16 p.
77. Dlustrated key to the genera of free-living marine nematodes of the order
Enoplida, by Edwin J. Keppner and Armen C. Tarjan. July 1989, 26 p.
78. Survey of fishes and water properties of south San Francisco Bay, California.
1973-82, by Donald E. Pearson. August 1989, 21 p.
79. Species composition, distribution, and relative abundance of fishes in the coastal
habitat off the southeastern United States, by Charles A. Wenner and George R.
Sedberry. July 1989,49 p.
80. Laboratory guide to early life history stages of northeast Pacific fishes, by Ann
C. Matarese, Arthur W. Kendall, Jr., Deborah M. Blood, and Beverly M. Vinter.
October 1989,651 p.

NOAA Technical Report NMFS 85

Marine Farming and Enhancement
Proceedings of the Fifteenth
U.S.-Japan Meeting on Aquaculture,
Kyoto, Japan
October 22-23, 1986
Albert K. Sparks (editor)
Panel Chairmen:
Conrad Mahnken, United States
Ikuo Ikeda, Japan
Under the U.S.-Japan Cooperative Programin Natural Resources (UJNR)March 1990

U.S. DEPARTMENT OF COMMERCE
Robert Mosbacher, Secretary

National Oceanic and Atmospheric Administration
John A. Knauss, Under Secretary for Oceans and Atmosphere

National Marine Fisheries Service
William W. Fox, Jr., Assistant Administrator for Fisheries

PREFACE_

The United States and Japanese counterpart panels on aquaculture were formed in 1969
under the United States-Japan Cooperative Program in Natural Resources (UJNR). The
panels currently include specialists drawn from the federal departments most concernedwith aquaculture. Charged with exploring and developing bilateral cooperation, the panels
have focused their efforts on exchanging information related to aquaculture which could
be of benefit to both countries.
The UJNR was begun during the Third Cabinet-Level Meeting of the Joint United StatesJapan Committee on Trade and Economic Affairs in January 1964. In addition to aquaculture, current subjects in the program include desalination of seawater, toxic microorganisms, air pollution, energy, forage crops, national park management, mycoplasmosis,
wind and seismic effects, protein resources, forestry, and several joint panels and committees in marine resources research, development, and utilization.
Accomplishments include: Increased communication and cooperation among technicalspecialists; exchanges of information, data, and research findings; annual meetings of thepanels, a policy-coordinative body; administrative staff meetings; exchanges of equipment,materials, and samples; several major technical conferences; and beneficial effects on
international relations.

Conrad Mahnken - United States
Ikuo Ikeda - JapanThe National Marine Fisheries Service (NMFS) does not approve, recommend or endorse any proprietary product or proprietary material mentioned
in this publication. No reference shall be made to NMFS, or to this publication furnished by NMFS, in any advertising or sales promotion which would
indicate or imply that NMFS approves, recommends or endorses any proprietary product or proprietary material mentioned herein, or which has asits purpose an intent to cause directly or indirectly the advertised product tobe used or purchased because of this NMFS publication.

ii

CONTENTS
Prentice, Earl F.
A new internal telemetry tag for fish and crustaceans 1
Matlock, Gary C.
Preliminary results of red drum stocking in Texas 11
Utter, Fred M., and James E. Seeb
Genetic marking and ocean farming 17
Smith, Theodore I.J.
Culture of North America sturgeons for fishery enhancement 19
Polovina, Jeffrey J.
Application of yield-per-recruit and surplus production models to fishery enhancement
through juvenile releases 29
Ito, Hiroshi
Some aspects of offshore spat collection of Japanese scallop 35
Westley, Ronald E., Neil A. Rickard, C. Lynn Goodwin, and Albert J. Scholz
Enhancement of molluscan shc.ifish in Washington State 49
Manzi, John J.
The role of aquaculture in the restoration and enhancement of molluscan fisheries inNorth America 53
Lee, Cheng-Sheng, and Clyde S. Tamaru
Application of LHRH-a cholesterol pellets to maturation of finfish: milkfish 57
Chew, Kenneth K.
Trends in oyster cultivation on the west coast of North America 65
Hirayama, Kazutsugu
A physiological approach to problems of mass culture of the rotifer 73
Fujita, Naoji, and Katsuyoshi Mori
Effects of environmental instability on the growth of the Japanese scallop Patinopecten yessoensis in
Abashiri sowing-culture grounds 81
Yamazaki, Makoto
Mantis shrimp: Its fishery and biological production 91
Inoue, Kiyokazu
Growth and survival of artificial abalone seed released in Shijiki Bay, Japan 101
Kimoto, Katsunori
Copepod swarms observed by SCUBA diving in a small inlet of Kyushu, Japan 105
Sudo, Hiroyuki
Feeding ecology of young red sea bream in Shijiki Bay 111
Fukuhara, Osamu
Importance of qualitative evaluation of hatchery-bred fish for aquaculture 117
Suda, Akira
Recent progress in artificial propagation of marine species for Japanese sea-farming andaquaculture 123iii

A New Internal
Telemetry Tag for
Fish and Crustaceans
EARL F. PRENTICE
Coastal Zone and Estuarine Studies
Northwest Fisheries Center
National Marine Fisheries Service, NOAA
Manchester Field Station
P.O. Box 130
Manchester, Washington 98353

The recognition of an animal or a group of animals within
a population is important for many reasons in fisheries research. Many types of tags and marks have been developed
to aid biologists in recognizing animals (Rounsefell 1963,
Farmer 1981). Unfortunately, no one technique has been
totally satisfactory from a biological or technical standpoint.
In 1983, the National Marine Fisheries Service began a study
supported by the Bonneville Power Administration to evaluate the technical and biological feasibility of adapting a new
identification system to salmonids. The system is based upona passive integrated transponder (PIT) tag. This tag has thepromise of eliminating some of the inherent problems withpresent tagging and marking systems. In addition to the research with salmonids, preliminary tagging studies have also
been conducted with two crustacean species. This paper
provides an overview of the basic tag operation, biologicalacceptability in test animals, field testing results, and a discussion of some of the possible applications of the PIT tag.

ABSTRACT
An ongoing cooperative agreement between the BonnevillePower Administration and the National Marine Fisheries Service
was initiated in 1983 to evaluate the technical and biologicalfeasibility of adapting a new identification system to salmonids.
The system is based on a passive integrated transponder (PIT)
tag. Each tag measures 12 mm in length by 2.1 mm in diameter and is uniquely coded with one of 34 billion codes. The tag's
operational life is unknown at this time; however, it is thought
to be 10 or more years. The tag can be detected and decodedin place, eliminating the need to anesthetize, handle, or restrain
fish during data retrieval.
Biological tests indicate the body cavity of juvenile and adultsalmonids is biologically acceptable for tag implantation. Comparisons between PIT-tagged and traditionally tagged andmarked juvenile salmonids are discussed. Laboratory and fieldtests showed that the PIT tag did not adversely affect growthor survival, nor was there any appreciable tissue response to
the tag. No evidence of infection due to tagging procedures wasobserved. Video-taped swim-chamber tests showed no significant effect of the PIT tag on respiratory rate, tail beat frequency,
stamina, or post-fatigue survival of juvenile salmonids. Tag
retention within the body cavity was near 100% for salmonids
weighing from 2 to 10,000 g. Previously PIT-tagged maturesalmon which were hand stripped of sperm and eggs showed
high tag retention with no adverse tag-caused effects.
During their outmigration, PIT-tagged juvenile salmonids
were successfully interrogated at two dams using automatic tagmonitoring equipment. All data were automatically recorded
and stored by computer. PIT-tag reading efficiency was 96 to
100%, while reading accuracy was over 99%. The tag-monitoring equipment proved to be reliable under field conditions.
Special tagging considerations with Crustacea and preliminary
testing ofthe PIT tag with two crustacean species are discussed,
along with future applications of the PIT tag to fisheries
research.

Tag operation_

The PIT tag consists of an antenna coil that has about 1,500
wraps of a special coated, 0.0254-mm diameter copper wire.
The antenna coil is bonded to a integrated circuit chip. The
electronic components of the tag are encapsulated in a glass
tube about 12 mm long and 2.1 mm in diameter (Fig. 1).
Each tag is preprogrammed at the factory with one of about
34 billion unique code combinations. The tag is passive,
having no power of its own, and thus must rely upon an
external source of energy to operate. A 400-KHz signal
energizes the tag, and a unique 40-50 KHz signal is transmitted back to the interrogation equipment where the codeis immediately processed and displayed, transmitted to a computer via an RS-232 interface, and/or placed on printed hard
copy. A portable hand reader (Fig. 2) or a fixed tag-monitor
system is used to interrogate and display the tag code information. Data transfer rate is 4,000 bits/so The interrogation
range of the tag varies with the monitoring equipment used:
Using a hand reader the reading range is up to 7.6 cm, whilewith a fixed full-loop interrogator the reading range of detection is about 18 em (Fig. 3). The tag can be read throughGlass tube

Antenna

Integrated
circuit chip

~ (((((((((((((((((((((((( ((((((((((~-------12mm---Figure 1
PIT tag.

_

270
250
/

230

/

/

/

PIT tagged group//
/

/

210

E

/

/

/

Control group

/

190

.s

.c

0, 170c::

2~Figure 2

0

u..

150

Portable hand-operated PIT-tag reader.
130
110
'I

90
Dual loop antenna assembly

I

I

'I

'I

'I

'I

~

'I

~

~

'I

/

Dual loop antenna assembly

70

o

150
Seawater
entry

100

150
200
Days

250

300

350

Figure 4
Comparison of length change between PIT-tagged (broken line) and control (solid line) fall chinook salmon (1984 brood) over time.

No special permits are required of the operator other thanthose obtained from the Federal Communications Commission (FCC) or their equivalent for the operation of lowpowered transmitting devices. These permits pertain only to
specialized monitoring systems and not the hand-held systemalready certified by the FCC. No special training or licensing of the operator is required to operate the tag-monitoring
equipment.
PIT tag operational life is currently being investigated.
Two 300-fish test groups ofjuvenile fall chinook salmon were
established: One control group (no tag), and one tag group.
All fish in each test group were weighed and measured at
the time the test groups were established. The two test groups
were maintained in freshwater until smolted and then transferred tQseawater where they are being held in separate sea
cages. Observations on growth, survival, and tag retention
and operation were made at various intervals. Results after
250 days show no meaningful difference in growth (Fig. 4)
or survival between groups of tagged and control fish. Tag
retention and operation have been 100%. Because of thepassive nature of the tag, an operational life of 10 years ormore is expected.

Figure 3
Typical PIT-tag monitoring system for dams.

soft and hard tissue, liquid (seawater and freshwater), glass,and plastic, but not through metal. Extreme heat or cold (60to -90°C) does not appreciably affect detection or readingof the tag. Successful tag monitoring can take place atvelocities up to 30 cm/s.

2

Biological suitability: Salmonids_

Table 1
Summary of wound condition after tagging and tag location within
the body cavity of juvenile faIl chinook salmon over time with descri~tions of wound condition and tag location codes.

It is important that a tagging system does not alter growth,survival, behavior, or reproduction. In addition, tag longevity(tag retention and operational life) is an important consideration. Laboratory tests were conducted to examine these factors as they apply to the use of the PIT tag with salmonids.
Juvenile and adult chinook (Oncorhynchus tshawytscha) ,Atlantic salmon (Salrno salar) , and steelhead (Salrno gairdneri) were used in the studies. The fish ranged in weight from
2 to 10,000 g. All tags were injected into the body cavity
using a modified hypodermic syringe and a 12-gauge needle(Prentice et al. 1986).

Days post-tagging
127

97

40-45

Code

Percent fish within a classification code
Wound code I
A
B

C

7.3
8.3
84.4

0
0
100.0

0.6
0.2
99.2

2.1
86.5
0.0
5.2
6.3

0
69.1
4.4
25.0
1.5

3.9
83.3
1.0
6.9
4.9

Tag location code2
A
B

Tissue response

C
D

Adverse tissue response to the tagging needle and tag has
been minimal. Tag-wound condition and tag placement within
the body cavity were documented by sacrificing groups ofjuvenile fall chinook salmon over time (Table I). In nearly
85 % of the fish examined (n = 195) the tag wound was completely healed by day 40-45, with only a scar indicating thearea of needle insertion. At the end of this same period, 7.3 %of the fish had an open wound and 8.3 % had a wound thatwas closed but slightly discolored. All fish (n = 99) sacraficed 97 days post-tagging showed complete healing of epidermal and subcutaneous tissue. A the termination of thestudy (day 127) an additional 102 fish were sacrificed; 99.2 %had completely healed tagging wounds, 0.6% had open
wounds, and 0.2 % had wounds that were closed but discolored. The study also indicated that once the tag was injected into the body cavity, its location was stable over time.
The majority of tags were found near the posterior end of
the pyloric caeca.

E'A Open wound.
B Wound that is closed by a thin membrane and is healing; at times
a slight red or pinkish coloration is noticeable in the area of thewound.
C Wound completely healed that mayor may not be noticeable by
the presence of a scar. No red or pink coloration in the area of
the wound.
2 A Tag located between pyloric caeca and mid-gut.
B Tag located near abdominal musculature and often embedded in
the posterior area of pyloric caeca near the spleen or in adipose
tissue at the posterior area of pyloric caeca.
C Tag found in an area other than those noted; generally between
mid-gut and air bladder or between liver and pyloric caeca.
D No tag present.
E Tag partially protruding through abdominal wall.

from each fish. Tag retention was 100% for the males. A
total of 48 females were spawned. Tag retention was 83 %for spawning females and 100% for non-spawners. Four tags
were passed during the first stripping and four tags during
the second-fourth stripping (Table 2). When a tag was passed,
it was easily recognized among the eggs. The presence oftags caused no observable adverse effects on the eggs.

Effects of maturing fish
Numerous morphological and physiological changes takeplace as salmon mature. These changes may alter the response of fish to foreign material such as a PIT tag. Furthermore, it is necessary to know whether a tag placed in the
body cavity would cause internal damage to eggs and whether
a tag would be retained during spawning. A study addressingthese issues was conducted using 21 male and 60 female
maturing Atlantic salmon. The fish ranged in weight from2,500 to 10,000 g and in length from 61 to 80 cm. All fish
were PIT tagged intraperitoneally using the method of Prentice et al. (1986). The fish were examined several times prior
to spawning to determine wound condition, tag retention,
readiness to spawn, and general condition, and scanned for tag
code using a hand-held scanning unit. When fish were determined to be ready to spawn, eggs were collected by hand stripping. Individuals that spawned were subject to 1-4 strippings.
During the study, no adverse tissue reaction was noted.
All tagging wounds were closed and healing by the third day
after tagging. No infection or discoloration was noted in thearea of the tag. All 21 males matured, and milt was collected

Table 2
Spawning dates and PIT-tag rejection by female Atlantic salmon.
DatespawnedNo. females
spawnedCumulative
no. spawned

21 Oct22 Oct23 Oct25 Oct29 Oct
4 Nov

21
4

21
25
32
39
42
48

7

7
3
6

No. tags
not retained'One tag not retained during 1st stripping.
bOne tag not retained during 3d and 4th stripping.
C One tag not retained during 1st, 2d, and 4th stripping.
dTwo tags not retained during 1st stripping.

3

Table 3
Comparison of survival, growth, and PIT-tag retention for the 1986 fall chinook salmon serial-tagging study.
Size (g)Treatment* andtest group

Survival

PIT-tag retention

No. days

(g)

start

end

(%)

(%)

Control well
Control-stream

202
200

135
135

4.9
5.1

24.9
24.8

100.0
99.0

PIT tagged
well #1
well #2
well #3
well #4

201
200
201
200

139
135
134
137

3.2
5.1
7.1
9.7

20.5
27.4
25.9
32.6

99.5
100.0
100.0
97.0

100.0
100.0
100.0
100.0

stream #1
stream #2
stream #3
stream #4

200
200
203
202

139
135
134
137

3.2
4.8
7.3
10.0

21.1
22.6
29.9
30.3

95.0
98.0
95.0
98.0

99.0
100.0
100.0
100.0

Test length*Well-constant temperature (~OoC) pathogen-free artesian well-water rearing; stream-ambient temperature (9.3-14.4°C) Bi
Beef Creek surface-water reanng.
g

Growth and survival

primarily in the stream-water ;,eld groups (Table 3). Visual
examination indicated that these populations of fish -were' invarious stages of smoltification. Reductions in immune response have been noted during smoltification (Maule andSchreck 1987). It is possible that exposure to pathogens inthe stream water, and/or smoltification status itself, contrib~ted to these mortalities. The data suggest that fish weighmg 3 g (mean weight) or less, or those undergoing smoltification, experience a low mortality (5 % or less) when PIT
tagged.

Tests were conducted in 1986 using juvenile fall chinook
salmon to detennine the minimum size that could be successfully.PIT tagged. Fish were tagged at four size ranges
and held m separate holding containers (Table 3). The number of fish in each test group ranged from 200 to 203. Fishranged in weight and length from 1. 7 to 14.9 g and 56 and120 mm, respectively, at the time of tagging. Two separate
water supplies (well water and stream water) were used in
the study to detennine if exposure to water containing fish
pathogens might affect tag-wound healing or tag retention.
Four sets of weight and length data were obtained on eachgroup of fish during a 134-139 day period. Tag retention
was excellent for both groups (99-100 %). Growth comparisons (both between the PIT-tagged well- and stream-watergroups, and with the control groups) indicated slight differences in length and weight at some sampling periods. However, there appears to be no observable pattern to the differences, suggesting that the glass-encapsulated PIT tag does
not compromise growth in juvenile salmonids reared in either~ell- or streamwater. Range of overall (134-139 days) surVIVal of PIT-tagged fish was 97-100% in the well-watergroups and 95-98 % in the stream-water groups. Visual inspection of the data (Table 3) shows that mortality occurredin the smallest size groups of fish for both well- and streamwater groups. Examination of mortalities for both initial welland stream-water groups showed perforation of the intestine
as the cause of death. Four of the seven mortalities in thefirst stream-water test group occurred within the first 2 days
after tagging and were from the first 10 fish tagged. Because
this was the first group of fish to be tagged in the year, ourtagging technique was not up to standard. Tagging technique
was refined and no further problems with intestinal perforation was observed in the other test groups. Mortality in thelarger size groups was variable (5% or less) and occurred

Effects on swimming ability
Tests were conducted to evaluate the physiological/behavioral
effects of the PIT tag on swimming ability in juvenile steelhead. The test were conducted in a modified version of a
Blaska respirometer-stamina chamber described by Smith andNewcomb (1970) (Fig. 5). Two size ranges of fish were~ested. The first group, tested in July 1985, averaged 81 mm
m length and 6.5 g in weight. The second test group, in
October 1985, averaged 112 mm in length and 17.2 g inweight. In both tests a random sample of fish (n = 2(0) wasremoved from the main population and intraperitoneallytagged with PIT tags using the procedures of Prentice et al.
(1986). A control (non-tagged) group (n = 2(0) was alsoestablished from the main population at this time. Swimming
tests were conducted on days 0 (same day as tagging), 1,
2, 3,4, 7, 9, 11, 14, 17,21, and 25, with 12 tagged and4 control fish tested each day. All tests were recorded onvideo tape and monitored at slow speed to detennine swim~g stamina.(time to impingement), tail-beat frequency per
mInute, respIratory rate (opercular rate/min), and stride
efficiency (no. tail beats/min required to maintain a unit
swimming speed of one body length/s). All tested fish (taggedand control) were held for 14 days post-test to establish stresssurvival profiles.
4

SIDE VIEW•

1. Variable speed control
2. Motor
3. Tachometer
4. Pulley
5. End plate
6. Propeller
7. Outer tube (plexiglass)
8. Inner tube (plexiglas)

9.
10.
11 .
12.
13.
14.
15.
16.

15

Electrified screen
Test compartment
Removable vane
Outflow
End plate (removable for fish loading)
Inflow
Axle for tilting chamber
Compartment divider

END VIEW

Figure 5
Blaska respirometer-stamina chamber.

chinook salmon, and steelhead. The tests were conducted at
Lower Granite Dam on the Snake River and McNary Damon the Columbia River. The survival of PIT-tagged fish wascompared with that of control fish (handled but not tagged),
coded-wire tagged (CWT), CWT plus cold branded, and cold
branded. Fish from all treatments were combined in a common holding cage, since each treatment could be recognizedby its identifying mark or tag. Five replicates of 25 fish per
treatment for a total of 125 fish per replicates were used in
the 1985 test. In the 1986 tests, 20 fish per treatment wereused for a total of 100 fish per replicate. The fish were heldfor 14 days in five cages that received a continuous supplyof untreated ambient river water. The fish were examined
daily for mortality.
No difference in survival between' fish injected with the
PIT tag and in the other treatment groups was noted at theend of 14 days of holding (Table 4). Mortality varied between dams but not between test groups at a dam. All PITtagged fish showed complete closure of the tagging woundat the end of 14 days. No infection or fungus was observed
around the tagging would prior to healing.

The swimming stamina, stride efficiency, and respiratory
rate data were compared between tagged and control fish,
and between post-tag testing data using the non-parametricMann-Whitney test. All data analyses followed the methodsof Sokal and Rohlf (1981). The data indicated that neither
the act of tagging nor the presence of the PIT tag compromised swimming stamina, stride efficiency, or respiratory rate ofjuvenile steelhead. In addition, post-test survival
was not affected by the PIT tag, and tag retention was 100%.
At the termination of the post-test holding period, all PITtagged fish were sacrificed and necropsies performed todetermine tissue reaction to the tags. No adverse tissue reactions or tag migrations within the peritoneal cavity werenoted.

Comparisons with traditional tagging
and marking methods
A series of tests comparing the PIT tag to traditional methodsof marking and tagging was conducted under field conditions using active, outmigrating spring chinook salmon, fall

Table 4
Summary of tests comparing the survival of PIT-tagged (ISh with that of traditionally tagged and marked fish at dams
along the Snake and Columbia rivers.
Survival (%)

Location

SpeciesDays
observed

Control

PIT

Cold-branded

CWT

CWT +
cold-branded

Lower Granite (1986)
Lower Granite (1986)

Spring chinook
Steelhead

14
14

95
100

98
99

96
100

97
99

99
97

McNary (1986)
McNary (1986)

Spring chinook
Steelhead

14
14

86
89

83
87

86
93

80
91

89
94

McNary (1986)
McNary (1985)

Fall chinook
Fall chinook

14
14

64
96

65
87

59
94

68
92

66
93

5

CANADA

IDAHO
I
I

~
Figure 6
Approximate Scaleo20

401-'T!

~

Location of hydroelectric dams on the Snake and Columbia rivers.

C-slotgatewellA-slotgatewellTransport
barge\
Raceways
Marking lL;~Jie:$t~
and/"
handling
facility

Wet separator
f- Bypass pipe

I

Transport
truck

Travelin£
screen:.

........ ;.~Figure 7
Typical hydroelectric dam with juvenile salmon collection facilities.

6

t

To
subsample...
UpwellInclinedscreen() Wetfl
X Qseparator()
X

PIT tagmonitors
E and Ff- To raceway or river2

PIT tagmonitors
Cand D

Sampletank

PIT tagmonitors
C and DPIT tagmonitors --->;~_____t

Aand BPIT tag

...

~

~

9

~

LL

Wet separator

monitors
E and F• ••.• FLOv.l'

Dewater
sections•
Raceways
Porosity control

10

PIT tagmonitors
A and B

Figure 9
Location of PIT-tag monitors at McNary Dam, Columbia River.

Figure 8
Location of PIT-tag monitors at Lower Granite Dam, Snake River.

cess. However, because of the unique features of the PITtag, it could be used in place of the traditional methods,
generating better results statistically while using significantly
fewer fish. With this goal in mind, prototype PIT-tag monitoring systems were installed at two dams. The monitors werelocated at the juvenile fish collection facilities at Lower
Granite Dam on the Snake River and McNary Dam on the
Columbia River. The monitors were placed in positions insuring that 100% of the fish exiting the wet separator weremonitored (Figs. 8, 9).
A series of tests was conducted to evaluate the operationalreliability, tag reading accuracy (correct decoding of the tag),and reading efficiency (percent tagged fish detected) of thedam PIT-tag monitors. Migrating juvenile spring chinook
salmon, fall chinook salmon, and steelhead were used as
experimental animals. The tests consisted of releasing 480
PIT-tagged fish in front of the tag monitors. Tag detection
efficiency ranged from 96 to 100%, while tag reading accuracy was over 99%. The monitoring equipment remainedin an active state at the dams for up to 7 months without major
problems. The PIT-tag monitoring system proved to be reliable, efficient, and accurate under field conditions.

Tag detection at dams
Outmigrating salmonids on the Columbia River system are
confronted with a number of hydroelectric dams that cause
decreased migration rates and increased mortality (Fig. 6).
Several of these dams have been modified to collect and/or
divert migrants around them as a method of increasing overall survival in the system. The collection facility generally
consists of a series of traveling screens that divert fish fromthe dam's turbine intakes and eventually into a gallery ofpipes that lead to a wet separator (Fig. 7). The separator
reduces the volume of water carrying the fish and removes
debris. Fish are then diverted either to a raceway for latertransport downstream via truck or barge, or directly to abarge for transportation downstream, or back into the river.
A subsample of the fish exiting the wet separator is diverted
into a holding tank and then to an observation room where
they are examined for tags and marks.
Traditionally, methods such as branding and coded-wiretagging (CWT) have been used to evaluate outmigration suc7

Table 5
Summary of data obtained from the release of PIT-tagged and cold-branded fish into McNary Dam Reservoir, Columbia River, 1985 and 1986.

Year

SpeciesTreatment

Total fish tagged
and branded

Pre-releasemortality (%)

Total fishhandledNo. fishobserved

Percent
observed

SD (%)

1985
1985

Fall chinook
Fall chinook

Branded
PIT tag

4,000
400

2.3
1.5

13,239
400

53
64

19.4*
16.2

9
4

1986
1986

Fall chinook
Fall chinook

Branded
PIT tag

5,000
500

3.8
3.6

201,670
500

95
142

27.4*
28.4

4
1

1986
1986

Spring chinook
Spring chinook

Branded
PIT tag

5,000
500

1.5
1.0

154,826
500

194
318

38.9*
63.6

10
2

*Expanded value to correct for subsampling at the dam.

Table 6
Summary of data obtained from the release of PIT-tagged and cold-branded fish from Dworshak National Fish Hatchery, Snake River, 1986.
Monitor location
Lower Granite Dam

SpeciesTreatment

Total fishhandledTotal
released

Pre-releasemortality(%)

Spring chinook
Spring chinook

Branded
PIT tagged

41,5842,500

40,675
2,450

2.2
2.0

474
464

Steelhead
Steelhead

Branded
PIT tagged

35,372
2,466

35,025
2,424

1.0
1.7

571
928

No. fishobserved

McNary Dam

Percent
observed

No. fishobserved

4,659

11.5
18.9

362
264

3,402

8.9
10.8

7,061

20.2
38.1

39
45

389

1.1
1.8

Expanded*

Expanded*

Percent
observed*No. fish observed multiplied by a factor to correct for subsampling at the darn.

Additional tests comparing branded and PIT-tagged juvenile migrants (fall chinook salmon, spring chinook salmon,and steelhead) were made in the field. The fish were released
into the Snake River of McNary Dam Reservoir and monitored as they passed through either Lower Granite Dam or
McNary Dam juvenile collection and monitoring facilities.
In order to obtain sufficiently accurate information on thebranded fish, large random subsamples of migrating juveniles, some of which were branded, were diverted into collection chambers. The subsampled fish were anesthetized andexamined visually for brands. On the other hand, PIT-tagged
fish were automatically interrogated as they passed by a dam
equipped with a PIT-tag monitor system. As each PIT-tagged
fish was detected, the tag information, time, date, and location of the fish was automatically entered into a computerand printer. Tables 5 and 6 summarize the results of thesetests. Because branded fish were subsampled, they weredetected at a much lower rate than PIT-tagged groups. An
expansion factor was applied to the brand information to obtain an estimation of the true number of branded fish collected (expanded observation value). Since the retrieval of
PIT-tag information is based on the monitoring of 100% of
the fish passing the collection facility at a dam, no expansion factor is required and 90-95 % fewer PIT-tagged fish
are needed for a study. Pre-release mortality in the branded

and PIT-tagged fish was similar for each test. Use of the PIT
tag also allowed the handling of substantially fewer fish than
did the branding technique to obtain statistically similar
results. Fish in the brand treatment were handled at the timethey were branded and again while being examined at thecollection facility, along with many nonbranded fish. PITtagged fish, on the other hand, were handled only at the timeof tagging. It is concluded that the PIT-tagged fish were notcompromised by the tag when released into a river or reservoir and that the PIT tag offers substantial gains in efficiency over branding for many applications.

PIT tagging of crustaceans_

Permanent identification using external tags and marks for
Crustacea has been difficult because of frequent molting. External tags and marks are often lost at the time of molting
or can interfere with the molting process, thus altering theanimal's behavior or physical well-being. Internal coded wire
(CWT) tags can eliminate the problem of tag loss at molting
but require the host to be sacrificed to retrieve the tag information (Prentice and Rensel 1977). The new PIT tag has thepotential to eliminate these problems. Preliminary experiments using the PIT tag with two species of Crustacea,
8

Citations

Macrobrachium rosenbergii and Cancer magister, have been
conducted. The prawns (n = 58) ranged in carapace lengthfrom 11 to 41 mm and in weight from 1.5 to 45.3 g. The
crabs (n = 52) ranged in width from 64 to 130 mm and inweight from 44.4 to 273.2 g. All crabs were tagged in thethoracic sinus (hemocoel) while the prawns were tagged ineither the thoracic sinus or abdominal musculature. Results
for both species showed that the tag was retained throughmolting and the tag information could be obtained rapidly
without sacrificing the tagged animal.

Future applications_

Farmer, A.S.D.
1981 A review of crustacean marking methods with particular reference to Penaeid shrimp. Kuwait Bull. Mar. Sci. 2:167-183.
Maule, A.G., and C.B. Schreck
1987 Changes in the immune system of Coho Salmon (Oncorhynchus
kisutch) during the Parr-to-Smolt Transformation and after Implantation of Cortisol. Can. J. Fish. Aquat. Sci. 44:161-166.
Prentice, E.F., and J.E. Rensel
1977 Tag retention of the spot prawn, Pandalus platyceras, injectedwith coded wire tags. J. Fish. Res. Board Can. 34:2199-2203.
Prentice, E.F., D.L. Park, T.A. Flagg, and S. McCutcheon
1986 A study to determine the biological feasibility of a new fish tagging system, 1985-1986. Report to Bonneville Power Admin., Contract DE-AI79-83BPI1982, Proj. 83-19, by Northwest Alaska Fish.
Cent., Natl. Mar. Fish. Serv., NOAA, 2725 Montlake Blvd. East,
Seattle, WA 98112, 879 p. + appendices.
Rounsefell, G.A.
1963 Marking fish and invertebrates. U.S. Dep. Int., Fish Wildl.
Serv., Bur. Commer. Fish., Fish. Leaflet 549, 12 p.
Smith, L.S., and T.W. Newcomb
1970 A modified version of the Blaska respirometer and exercise
chamber for large fish. J. Fish. Res. Board Can. 27:1331-1336.
Sokal, R.R., and F.J. Rohlf
1981 Biometry. W.H. Freeman and Co., San Francisco, xx p.

_

Based upon biological and technical information gathered todate and its unique characteristics, the PIT tag will become
a valuable tool for a variety of applications in the laboratory
and field. Its use will not be limited to salmon, prawns, andcrabs but will be applicable to any animal that can accept
and retain the tag without compromise. Examples of advantages and applications of the PIT tag include: (1) Individual
identification of broodstock; (2) use with groups of animals
where serial measurements, e.g., growth, of individual
animals are required without sacrificing the animal; (3)reduction in the number of replicated treatments in a study
because each animal is uniquely numbered and can be treatedas a replicate; and (4) the ability to physically combine different treatments, since individual animals can be identified,removing the variable of rearing-container effect. Other applications might include use in behavioral studies where themovement of animals can be monitored automatically or
through capture-recapture methods. It is conceivable that one
could monitor bottom-dwelling PIT-tagged individuals
through a grid monitor or a monitor system mounted to anunderwater sled.
The main limitation to the use of the PIT tag, other thancost and physical and operational constraints, lies, as withmost tools, in our imagination. The PIT tag is only the first
generation of a number of sophisticated identification systems growing out of our computer age. We must utilize thefull potential of these new tools if we are to meet the many
challenges of fisheries enhancement and aquaculture.

9

Preliminary Results of

Red drum (Sciaenops oee/latus) is a quasicatadromous
sciaenid that ranges from Tuxpan, Mexico, in the Gulf of
Mexico to Massachusetts in the Atlantic Ocean (Matlock1984). Adults spawn in oceanic waters nearshore, and larvae are carried by currents through passes into estuarine
nursery areas where they remain for 3 to 5 years before
returning to the ocean to spawn. Economically important
sport and commercial artisinal fisheries have existed sincethe 1800s in Texas, Louisiana, and Florida (Matlock 1980).
However, harvest is being increasingly restricted to insure
adequate reproduction and growth to maintain the fishery.
No red drum caught in Florida or the U.S. Fishery Conservation Zone in the Gulf may be retained, and fish caught
in Texas and Alabama may not be sold. Size, bag, andpossession limits exist in all five Gulf states. For example,
only five red drum, all between 457 and 762 mm TL (total
length), can be retained per day in Texas. However, harvest
regulations are not the only options available to managers.
Stocking red drum reared in captivity has recently become
another management tool for this fishery (Rutledge andMatlock 1986). In 1974 red drum were first spawned andreared in captivity (Arnold et al. 1977). The spawninginducement technique, i.e., temperature and photoperiodmanipulation, was refined so that fry could be obtained at
any time (Colura et al. 1976). With fry readily available,
fingerlings could be produced in ponds throughout the year,
and the potential for improving the red drum fishery throughstocking could be examined.
Enhancement of wild populations through stocking appeared feasible. Historic bag seine and trammel net collections indicated the habitat could support more red drum thanwere present in the 1970s (Matlock 1984). A preliminary
evaluation of a limited stocking indicated that stocked fishsurvived, grew, and supplemented the juvenile populationin the stocked bay (Matlock et al. 1986). However, too few
fish were stocked to detect any impact on recruitment to thefishery.
These initial results were sufficient to convince sport fishermen, a major electric utility company, and the Texas Legislature that a red drum hatchery could be beneficial. The Gulf
Coast Conservation Association donated $1.4 million to build
the facility (Rutledge and Matlock 1986), Central Power andLight Company provided the land, and the Texas Legislatureappropriated about $160,000 operating expenses for staff andequipment. The hatchery was designed to produce about 10
million fingerlings annually from 8 ha of earthen ponds. In
each of the first 3 years of operation (1983-85), 7 to 9 million
fingerlings were produced (McCarty et al. 1985, Matlock1986). However, the impact of these stockings on sport
angler landings has not been determined.
The objective of this paper is to present a preliminary
assessment of the success of 2 years of stocking red drum
fingerlings into two Texas bays.

Red Drum Stocking
in Texas
GARY C. MATWCK
Texas Parks and Wildlife Department
4200 Smith School Road
Austin, Texas 78744

ABSTRACTThe ability to control spawning and to rear red drum (Sciaenops
ocellatus) in captivity has afforded managers the opportunity
to use stocking to enhance native fISheries. This paper presents
preliminary results of the effects of 2 years of intensive stocking in two Texas estuaries. Catch rates in gill nets fIShed randomly in stocked and unstocked bays in spring (April-June) andfall (September-November) were compared to determinechanges in relative abundance of fishable populations. Landings by private sport-boat anglers in each bay during the lowuse (mid-November through mid-May) and high-use (mid-May
through mid-November) seasons before and after stocking werecompared for fISh ~450 mm total length. Relative abundance
and angler landings of red drum were higher after stocking inthe stocked bay; abundance and angler landings were similar
or lower in unstocked bays after the stocking dates. Additional
research is needed to determine optimum stocking rates, times,
and fish sizes.

11Materials and methods_

Red drum fingerlings (11-83 mm TL) were spawned andreared in earthen ponds (0.8 ha) at the John Wilson Marine
Fish Hatchery (McCarty et al. 1985). Fish were transported
to stocking sites (Fig. 1) in trailers fitted with a three-ehambertank: (3.0 X 1.2 X 0.8 m) that was supplied with compressed
oxygen to maintain 4-10 ppm (Hammerschmidt and Saul
1985). Each chamber held about 1,950 L of water and contained 10 ppm furacin.
Fish were either stocked directly into the bay or transferredthrough a plastic pipe to tanks on a barge by gravity flow
and then transported to stocking sites. Fish were acclimatedto ambient water temperature and salinity (±rC and 5 ppt)
at each site by exchanging water in the tanks at a rate of about
2,600 Llh. Release mortality was estimated for each loadby holding 25 fish in each of 3 or 4 cages for 24 hours at
the release site (Hammerschmidt and Saul 1985).
About 14 million fish were released in 1983, late 1984,and early 1985 into the San Antonio and Corpus Christi Bay
systems (Fig. 1). The San Antonio Bay system received 2.3
million fish in May 1983 and 6.0 million fish in May andJuly 1984 (Matlock 1986). The Corpus Christi Bay system
received 4.7 million fish in September and November 1983
and 250,000 in January 1985. The objective of these releases
was to increase significantly (P = 0.10) the number of red
drum landed by sport-boat anglers over the historic harvestin these two bay systems. These two bays were selected
because they have diverse habitats and fishing pressures, no
netting is allowed, the ratio of surface area to number ofanglers was among the lowest on the coast, and the historic
landing rates for red drum were among the highest on the
coast. These characteristics should have maximized the probability of determining if the objective was met. They would
also allow the inference that if stocking was effective in thesebays, then it should be effective in all other bays where
historic landing rates were less.
The effect of stocking was measured in four ways. Cage
studies (described previously) were used to determine initial survival after stocking. Bag seines were pulled at stocking sites for ~3 months after stocking to determine longerterm survival (>0 %). Ongoing surveys of sport-boat anglers(Osburn and Ferguson 1986) and fishery-independent monitoring with gill nets (7.6, 10.2, 12.7, and 15.2 cm stretchedmeshes) in the two stocked bays and one unstocked bay(Crowe et al. 1986) were used to measure changes in anglers'landings and red drum relative abundance. Trends in mean
landing rates in stocked bays were compared with the unstocked bay.

GULF OF MEXICOLOWER LAGUNA MADRE

MEXICO

Figure 1
Bay systems of Texas coast. Red drum were stocked in the San Antonio
and Corpus Christi Bay systems.

Results and discussion_

Stocked fish survived the stocking process very well. The
mean (± 1 SE) 24-hour survival of fish held in cages was
89.4+2.7% in 1983 and 86.2±2.2% in 1984 (Hammerschmidt and Saul 1985, Hammerschmidt 1986). Juvenile fish
were recaptured in bag seines in both stocked bay systems
for up to 1.5 months after stocking (Dailey and McEachron1986). Thereafter, fish were large enough to escape bagseines (Matlock 1984).
Stocking appears to have increased the number of red drum
available for harvest in Texas bays. However, this impact
was not consistent among all stockings because of a major
fish kill caused by record-breaking freezing temperatures during late December 1983 and early January 1984 (McEachron
et al. 1984). Over 90,000 red drum were killed coastwide,and most of the dead fish were found in the San Antonio
Bay system. The mean catch rates in gill nets in the stocked
Corpus Christi Bay system were much higher in the 2 years
after stocking than in the years before stocking (Fig. 2). Mean
catch rates in the upper Laguna Madre (control) were also
higher after stocking, but were not as great as in the stockedbay. The increased catches in fall 1984 and 1985 in thestocked bay were primarily in the 7.6-cm stretched mesh,
12

0.8

~

STOCKED

0

UNSTOCKEO

I

0.6

I0(

II:
CI

Z

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Q

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ll'i!lll'i!l~ll'i!lll'i!l

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'83

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.--

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'85

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Figure 2

12.7cmMean catch rate (no.lh) of red drum in gill nets in the Corpus Christi
Bay (stocked) and upper LagwJa Madre (unstocked) systems in fall (SeptNov) and spring (April-June) during 1983-86. The historic mean fall
catch rate (for the period 1975-83) is also shown. Stocking occurredin fall 1983 (4.7 million fish) and January 1985 (250,000).

FAll
'83

FALL
'84

SPRING
'85

FALL
'85

SPRING'86

Figure 3
Mean catch rate (no./h) of red drum in the 7.6, 10.2,
and 12.7 cm stretched-mesh portions of gill nets in the
Corpus Christi Bay (stocked) and upper Laguna
Madre (unstocked) systems, fall (Sept-Nov) and spring(April-June), during 1983-86. Stocking occurred in fall1983 and 1984.

but this pattern did not occur in the unstocked bay (Fig. 3).
This reflects recruitment of stocked fish to the 7.6-cm
stretched mesh 1 year after each stocking. The stocked fish
were evident in each subsequent season in the larger meshportions of gill nets. In the San Antonio Bay system, the meancatch rate in gill nets decreased after the 1983 stocking, but
increased after the 1984 stocking (Fig. 4). Apparently very
few of the 2.3 million fish stocked in 1983 survived thisfreeze. The mean catch rate in gill nets in spring 1984 (0.2
fish/h) was among the lowest recorded since 1975 (Fig. 4).
However, wild fish may have been more affected thanstocked fish. The mean catch rate of age-I wild fish, thosein the 7.6-cm stretched mesh part of the nets, declined to
the lowest level ever «1 fish/h), while catches in the larger
meshes did not decline. Fish stocked in July 1984 were first
apparent in gill nets in fall 1985, and the mean catch rate
in gill nets was the third highest on record (Fig. 4). Most(83%) of this catch was in the 7.6-cm stretched mesh.
Stocking apparently increased the fishing success of sportboat anglers for red drum. The mean landing rate by thesefishermen increased 150% over the mean historic (1979-84)
rate in the stocked Corpus Christi Bay system in the highuse (15 May-15 November) season of 1985 (Fig. 5) whenstocked fish reached the minimum legal size limit of 457 mm.
The mean landing rate also increased in the unstocked upper
Laguna Madre, but by only 50%. The mean landing rate in
the following low-use season (16 November-14 May) in
1985-86 was similar to the historic catch rate in the stocked

bay, but it declined in the unstocked bay. The number of
red drum landed from the stocked bay also increased 100%over the historic mean in 1985-86 (Fig. 6). Landings in theunstocked bay increased only 27% from the historic mean,although anglers fished 45 % more man-hours in the unstocked bay than in the stocked bay in 1985-86 (882 vs. 609
man-hours). The increased landings over the historic meanin the upper Laguna Madre (18,500 vs. 14,600 fish, respectively) would have been much less than 27% had the unusually low 1984-85 landings (3,800 fish) not been included
in calculating the historic mean. Annual landings in all otheryears in the upper Laguna Madre were 13,100 to 25,700 fish
and averaged 16,800 fish.

13

2.0

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CI

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a:

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~

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U

0.4

Figure 4
Mean catch rate (no.lh) of red drum in giU nets in the
San Antonio Bay system, faD (Sept-Nov) and spring (AprilJune), during 1975-86. Arrows indicate dates of major
events affecting red drum. Fish were stocked in spring
1983 (2.3 million) and in summer 1984 (6.0 million).

0-4---------------------5 F

5 F

5 F

5 F

5 F

5 F

5 F

5 F

5 F

5 F

5 F

5 F

757677787980818283848586

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w

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STOC!!!!GI.

UNSTOCKED

~

~

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~
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Hislo,ic

PO,I

Me."

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caS·'1I6)

Figure 5
Mean landing (catch) rate (no./man-hour) of red drum landed by
sportboat anglers in the Corpus Christi Bay (stocked) and upper
Laguna Madre (UDstocked) systems before and after fISh reachedminimum size Omits of 457 mm TL in the high-use (15 May-20 Nov)and low-use (21 Nov-14 May) season during 1979-86.

Number of red drum landed annually (15 May-14 May) by
sportboat anglers in the Corpus Christi Bay (stocked) andupper Laguna Madre (unstocked) systems before and after
stocked fISh reached minimum size Omit of 457 mm TL.

Stocking also benefited anglers in the San Antonio Bay
system. Although the 1983-84 freeze greatly reduced thenumber of available fish, the anglers' mean landing rateincreased from the 1982-83 low-use season in the San Antonio Bay system in that low-use season when stocked fish
became retainable by anglers (Table 1). The mean catch rate
also increased in the adjacent Matagorda Bay system; somefingerlings may have moved to this system. Mean landing
rates in other bays either remained the same, decreased, or
remained less than 0.1 fish/man-hour. Landings during the
low-use 1984-85 season (5,800 fish) were about the sameas the historic mean (6,200 fish) although effort (36,200 manhours) was about 50% less. Fish stocked in 1984 are justnow becoming retainable by fishermen.
Wild stocks of red drum can be enhanced through stocking to provide improved fishing success. However, thedegree of improvement depends on such factors as the carrying capacity of each system, the number of wild fish present
before stocking, fishing pressure, harvest restrictions, andclimatic events. The sale of red drum caught in Texas wasprohibited 2 years before stocking the Corpus Christi Bay
system. About 3 months after the first stocking, the Texas

Figure 614

Table 1
Mean catch rate (no.lman-hour) of red drum landed by private sport-boat anglers in Texas bay systems
during the low-use (21 Nov-14 May) seasons, 1982-83 and 1983-84.

Year

GalvestonMatagorda

San
Antonio

1982-83
1983-84

0.01
0.01

0.03
0.07

0.04
0.13

AransasCorpusChristiUpper
LagunaMadre

Lower
Laguna
Madre

0.07
0.06

<0.01
0.05

0.01
0.01

0.05
0.04

Citationscoast experienced the worst freeze in history. The minimum
size limit was increased from 406 to 457 mm, and the bag
and possession limits were reduced by 50%. The existingand subsequently imposed restrictions reduced the impact of
the freeze on red drum. Fishing improved in the upper
Laguna Madre even without stocking; however, this improvement was even greater with stocking.
Additional research is needed to determine optimum stocking rates. An intensive stocking of fish marked with coded
metal tags or genetically marked fish could be used to improve estimates of natural mortality rates and the contribution of stocked fish to the wild stocks and angler harvest.
These preliminary results are not based on a rigorous
statistical analysis of the data collected. The landings data
have not been adjusted for changes in minimum size limits
or bag and possession limits. Therefore, the conclusions
presented are conservative. A more rigorous analysis isplanned after the 5-year project ends in 1988 and all stockedfish have left the estuarine fishery.

_

Arnold, C.R., J.D. Williams, A. Johnson, W.H. Bailey, and J.L.
Lasswell1977 Laboratory spawning and larval rearing of red drum and southern flounder. Proc. ADDU. Conf. S.E. Assoc. Fish Wild\. Agencies 31:437-441.
Colura, R.L., B.T. Hysmith, and R.E. Stevens
1976 Fingerling production of striped bass (Morone saxatilis), spotted
seatrout (Cynoscion nebulosus), and red drum (Sciaenops ocellata)
in saltwater ponds. Proc. World Maricult. Soc. 7:79-92.
Crowe, A.L., L.W. McEachron, and P.C. Hammerschmidt
1986 Trends in relative abundance and size of selected finfish in Texas
bays: November 1975-December 1985. Tex. Parks Wild\. Dep.,
Coast. Fish. Br. Manage. Data Ser. 114, Austin, TX, 259 p.
Dailey, J.A., and L.W. McEachron
1986 Survival of unmarked red drum stocked into two Texas bays.
Tex. Parks Wild\. Dep., Coast. Fish. Br. Manage. Data Ser. 116,
Austin, TX, 8 p.
Hammerschmidt, P.C.
1986 Initial survival of red drum fingerlings stocked in Texas bays
during 1984-1985. Tex. Parks Wild\. Dep., Coast. Fish. Br.
Manage. Data Ser. 106, Austin, TX, 14 p.
Hammerschmidt, P.C., and G.E. Saul
1985 Initial survival of red drum fingerlings stocked in Texas bays
during 1983. ADDU. Proc. Tex. Chap. Am. Fish. Soc. 7: 13-28.
Matlock, G.C.
1980 History and management of the red drum fishery. Proc. Gulf
States Mar. Fish. Comrn., Pub\. 5, Ocean Springs, MS, 37-53.
1984 A basis for the development of a management plan for red drumin Texas. Ph.D. diss., Texas A&M Univ., College Station, TX,
291 p.
1986 A summary of 10 years of stocking fishes into Texas bays. Tex.
Parks Wildt. Dep., Coast. Fish. Br., Manage. Data Sec. 104, Austin,
TX, 19 p.
Matlock, G.C., R.J. Kemp, Jr., and T.L. Heffernan
1986 Stocking as a management tool for a red drum fishery, a preliminary evaluation. Tex. Parks Wild!. Dep., Coast. Fish. Br.,Manage. Data Ser. 75, Austin, TX, 27 p.
McCarty, G.E., J.G. Geiger, L.N. Sturmer, B.A. Gregg, and W.P.
Rutledge
1985 Marine finfish culture in Texas-Model for the future. Proc.
World Maricult. Soc. 15: 120-131.
McEachron, L.W., G. Saul, J. Cox, C.E. Bryan, and G. Matlock
1984 Fish kill. Tex. Parks Wild\. Mag. 42(4): 11-13.
Osburn, H.R., and M.O. Ferguson
1986 Trends in finfish landings by sport-boat fishermen in Texas
marine waters, May 1974-May 1985. Tex. Parks Wildt. Dep.,
Coast. Fish. Br., Manage. Data Ser. 90, Austin, TX, 448 p.
Rutledge, W.P., and G.C. Matlock
1986 Mariculture and fisheries management-A future cooperative
approach. In Stroud, R.H. (ed.), Fish bulture in fisheries management, p. 119-127. Proc., Int. Symp. on Use of Culture in Fisheries
Management. Am. Fish. Soc., Bethesda, MD.

15

Genetic Marking andOcean Farming!

Individuals from discrete subgroups within a species usually lack readily visible characters (or marks) that permit
subgroup classification. More subtle distinguishing characteristics sometimes become apparent through specialized
procedures, and various methods have been devised to impose identifiable attributes on individuals within a group (i.e.,
marking). Most commonly used marks are restricted to theimmediate generation because they are largely or entirely
not heritable.
Completely heritable characters, particularly allelic protein genes detected by electrophoresis, have proven to bevaluable genetic marks. Previously unknown geneticallyisolated subgroups of many fishes have been identified(Allendorf et al. 1987). This information has been used tomonitor migrations of distinct groups in stock mixtures (e. g. ,Milner et al. 1985). Natural genetic differences between
populations have been used to estimate proportions of stocked
and unstocked fish in specific fisheries (e.g., Murphy et al.
1983).
Intentional breeding using distinct genotypes (i.e., genetic
marking) has been used to create identifiable groups. Experimental applications of genetically marked groups haveincluded measurements of growth and survival of wild,
hatchery, and hybrid steelhead in different environments(ReisenbicWer and McIntyre 1977), quantifying contributionsof chum salmon males of different behavioral states (Schroder1982), and identifying differing fertilization rates of spermfrom individual pink salmon males examined under varying
conditions (Gharrett and Shirl~y 1985).
Genetically marked populations have also been created andmonitored. Two concerns that must be met if the marked
populations are to approximate the long-term performancepotential of the parent stock are (1) a negligible effect on
performance of individuals having different genotypes forthe alleles involved in the marking process, and (2) an adequate sampling of genes over all loci from the parent stockin the marked population. Guidelines relating to the first concern are listed below:
I Be particularly cautious of variants where good evidence
for selection has been indicated in other organisms for particular protein classes.
2 Seek variants that occur widely and in diverse environments.
3 Be careful of rare alleles or those with substantial frequencies in restricted environments.
4 Monitor the performance of comparable marked andunmarked individuals and populations.
The second concern relates to the effective numbers ofbreeding individuals in the founding populations and in subsequent generations. Guidelines (suggested by Allendorf and
Ryman 1987) include:
1 Use 25 individuals of each sex (with equal contributions from individual matings) as an absolute minimum forestablishing a new population.

FRED M. UTTER
Coastal Zone and Estuarine Studies
Northwest Fisheries Center
National Marine Fisheries Service, NOAA
2725 Montlake Boulevard East
Seattle, Washington 98112

JAMES E. SEEB
Department of Zoology
Southern Illinois University
Carbondale, Illinois 62901'The information in this extended abstract is included in the following
article: Utter, F.M., and J.E. Seeb. In press. Genetic marking in fishes:
Overview focusing on protein variation. Trans. Am. Fish. Soc.

17

Citations

2 Use a considerably larger number of individuals formaintenance of established populations.
Two projects involving Pacific salmon species demonstrate
somewhat different applications of genetically marking populations. A segment of a chum salmon run to a stream in
Puget Sound, Washington, USA, was genetically marked forfive consecutive years using males having selected genotypes
for two enzyme systems mated with randomly chosen females(Seeb et al. 1986). Allele frequency differences between
marked groups and the parent population (10% or greaterfor both enzyme systems) resulted in estimates of enhancement contributions to the total returning adult populationsin the stream from 6 % to 29 %. Dilution of the mark in theadjacent inlet resulted in estimates between 2.2 and 4.3
million juvenile fish.
Late-returning segments of even- and odd-year runs of pinksalmon were genetically marked for four consecutive years
at a hatchery on a stream near Juneau, Alaska, USA (Lane
1984, Gharrett 1985); different single enzyme marks wereused for even- and odd-year runs. Both males and females
were selected for breeders, permitting a much larger changeof allele frequency between the parent and marked populations. No straying to adjacent drainages was detected for
either year-class. Evidence of straying within the drainageof the parent population was observed only for the late segment of the even-year run both upstream and downstream
from the hatchery.
Genetic marking projects similar to those summarized
above are feasible for any cultured population. Cultured
marine species are particularly suitable for genetic marking;their generally reduced genetic divergence relative to freshwater and anadromous species (Gyllensten 1985) makes
marked populations more readily apparent amidst a more
uniform background. Genetic marking can also be extended
to wild populations, providing potential breeders can be intercepted, genotyped, and only those of appropriate genotype
permitted to spawn.
Genetic marking provides a heritable brand with diverse
uses. Marked populations permit monitoring of intermingling
and interbreeding with other populations. This capability
relates to environmental and genetic concerns about intentional or accidental releases of cultured or transplanted
populations. Conversely, genetically marked populations canbe used by their owners or stewards for identification in
mixed harvests.
Although protein coding genes are presently the mostuseful source of materials for genetic marking, they represent less than 1 % of the total DNA of an organism. Much
additional genetic variation exists that is potentially usefulfor genetic marking. The DNA of mitochondria is a sourceof variation that is finding increasing application as a population marker (e.g., Ferris and Berg 1987). Immunologicallydetected genetic markers are another souce of variation that
may be useful. The same principles concerning the performance of genotypes and the adequacy of effective population size pertain to any genetic mark that is used.

_

Allendorf, F., and N. Ryman
1987 Genetic management of hatchery stocks. In Ryman, N., andF. Utter (oos.), Population genetics and fishery management, p. 141159. Univ. Wash. Press, Seattle.
Allendorf, F., N. Ryman, and F. Utter
1987 Genetics and fishery management: Past, present, and future. In
Ryman, N., and F. Utter (oos.), Population genetics and fishery
management, p. 1-20. Univ. Wash. Press, Seattle.
Ferris, S.D., and W.J. Berg1987 The utility of mitochondrial DNA in fish genetics and fishery
management. In Ryman, N., and F. Utter (oos.), Population genetics
and fishery management, p. 277-299. Univ. Washington Press,
Seattle.
Gharrett, A.J.
1985 Genetic interaction of Auke Creek Hatchery pink salmon withnatural spawning stocks in Auke Creek. Rep. SFS UAJ-8509, Univ.
Alaska, Juneau, 40 p.
Gharrett, A.J., and S.M. Shirley
1985 A genetic examination of spawning methodology in a salmon
hatchery. Aquaculture 47:245-456.
Gyllensten, U.
1985 The genetic structure of fish: Differences in the intraspecificdistribution of biochemical genetic variation between marine, anadromous, and freshwater species. 1. Fish. BioI. 26:691-699.
Lane, S.
1984 The implementation and evaluation of a genetic mark in a
hatchery stock of pink salmon (Oncorhynchus gorbuscha) in southeast Alaska. MS thesis, Univ. Alaska, Juneau, 107 p.
Milner, G., D. Teel, F. Utter, and G. Winans
1985 A genetic method of stock identification in mixed populationsof Pacific salmon. Oncorhynchus spp. Mar. Fish. Rev. 47(1): 1-8.
Murphy, B.R., L.A. Nielsen, and B.J. Turner
1983 Use of genetic tags to evaluate stocking success for reservoir
walleyes. Trans. Am. Fish. Soc. 112:457-463.
Reisenbichler, R.R., and J.D. McIntyre
1977 Genetic differences in growth and survival of juvenile hatcheryand wild steel head trout, Salmo gairdneri. J. Fish. Res. Board Can.
34: 123-128.
Schroder, S.L.
1982 The influence of intrasexual competition on the distribution ofchum salmon in an experimental stream. In Brannon, E.L., and E.O.
Salo (eds.), Salmon and trout migratory behavior symposium, p.
275-285. Coli. Fish., Univ. Wash., Seattle.
Seeb, J., L. Seeb, and F. Utter
1986 Use of genetic marks to assess stock dynamics and management
programs for chum salmon. Trans. Am. Fish. Soc. 115:448-454.

18

Culture of North American
Sturgeons for Fishery
Enhancement1,2

Sturgeons can be considered' 'living fossils," exhibiting littlechange from their sturgeon-like ancestors of the upper Cretaceous period, 100 million years ago. Worldwide, there are
25 species of sturgeons, 18 of the genus Acipenser, two of
the genus Huso (which contains the largest sturgeon), two
shovelnose sturgeons (Scaphirhynchus) , and three of thegenus Pseudoscaphirhynchus. In North America, there areeight species inhabiting various freshwater and/or coastal
habitats (Table 1). Of these, Atlantic sturgeon Acipenser
oxythynchus, lake sturgeon A. fulvescens, shortnose sturgeon
A. brevirostrum, white sturgeon A. transmontanus, andpaddlefish Polyodon spathula, have received substantial
interest in recent years for purposes ranging from stockenhancement to commercial aquaculture.
Historically, sturgeons were important to early settlers andserved as an item of commerce. Reports and books in colonialdays often contained information on the abundance of theseawesome creatures which the indians named "MisheNahma" or "King of Fishes. " Large-scale commercial exploitation of North American sturgeon stocks began during
the last quarter of the 19th century. The rapidity with which
the major stocks were depleted astonished fishermen andfishery managers. The statement by Tower (1909) typifies
the thoughts and feelings of the time- "It seems scarcely
comprehensible that a fish so widely distributed through thecountry, so abundant, and so little used less than three
decades ago, has so rapidly disappeared that the end isalready in sight." This overutilization of the sturgeons aswell as other natural resources was responsible for the initiation of a conservation movement around 1907. Such conservation efforts, however, came too late to have any significant impact on the sturgeons.
Today, only remnant populations remain of most major
North American stocks of sturgeons" and their geographic
ranges have been sharply reduced from those of only 100
years ago. The purpose of this report is to briefly review
the early and current sturgeon fisheries and to discuss theculture efforts for fishery enhancement of North American
sturgeons, focusing on the more important Atlantic, lake,shortnose and white sturgeons, and the paddlefish.

THEODORE I.J. SMITH
South Carolina Wildlife and Marine Resources Department
P. O. Box 12559
Charleston, South Carolina 29412

ABSTRACT
North American sturgeons were important to early colonists,
and about 1860 large-scale exploration was initiated. However,by the turn of the century, most sturgeon stocks were severely
depleted and the major fisheries collapsed. Early fishery managers sought to rehabilitate the stocks through propagated fish,
but suitable culture efforts could not be developed and efforts
were abandoned by about 1910.
In recent years, protection of some sturgeon stocks has resulted from enactment of controlled fishing regulations and/or
listing species as an endangered species. Renewal interest has
focused on spawning and culture of most North American sturgeons, and today there are small-scale stocking efforts underway with several species.

Exploitation of sturgeons_

Early fisheries
Utilization of North American sturgeons varied according
to species, area, and time. During the early to mid-19th century, sturgeons were not higWy regarded. At this time, they
were intentionally killed to reduce damage to fishing nets,
fed to livestock, used as fertilizer and to fuel boilers of steamboats (Harkness and Dymond 1961, Galbreath 1985). However, sturgeons eventually became highly prized and werevalued as the most expensive freshwater fish. Large-scale
exploitation began around 1860 when it was learned thatsmoked sturgeon could be substituted for smoked halibut and'Contribution No. 219 from the South Carolina Marine Resources Center.
zPreparation of this report was supported by the U.S. Fish and Wildlife
Service, Contract Number S.C.-AFS-11 and the State of South Carolina.
19

Table 1
Geographical distribution and general habitat of North American sturgeons.
SpeciesCommon name

Geographical distribution

Habitat

Shortnose sturgeon

Atlantic coast from SI. John River, New Brunswick, Canada,
to St. Johns River, east coast of Florida

Anadromous; large coastal rivers

fu/vescens

Lake sturgeon

Mississippi River, the Great Lakes, and the Hudson Bay
drainage basim

Freshwater; lakes and large rivers

medirostrisGreen sturgeon

Pacific coast from Gulf of Alaska south to North Baja, California, especially the Columbia River

Anadromous; primarily estuarine

oxyrhynchus

Atlantic sturgeon

Atlantic coast from Labrador through Gulf of Mexico tonorthern coast of South America

Anadromous; primarily estuarinetransmontanus

White sturgeon

Pacific coast fom Gulf of Alaska south to north Baja, California, especially Columbia River and Sacramento-San
Joaquin system

Anadromous or semi-anadromous;large flowing rivers

Scaphirhynchus
a/bus

Pallid sturgeon

Mississippi River from Dlinois south to Louisiana, Missouri
River from Montana to Missouri
Ohio, Mississippi, and Missouri Rivers; Mobile Bay drainage, Alabama River, Rio Grande in Texas and New Mexico

Freshwater; large turbid flowing
riversAcipenser
brevirostrum

p/atorhynchus
Po/ydon spathu/a

Shovelnose sturgeon
Paddlefish

Mississippi River system, Mobile Bay drainage, Alabama
River west to east Texas

that the eggs could be made into high-quality caviar. Besides
these products, isinglass was derived from the swim bladder and cartilagenous backbone of sturgeons and used toclarify liquids and stiffen jams and jellies; fish oil could be
rendered from the flesh and used in paints; and leather was
made from the skin. However, the main products were theflesh and the caviar, as is the case today.
Generally, sturgeon fishing occurred during the spring asadults migrated to freshwater spawning areas, although somespecies, such as the white sturgeon, were harvested on theirfeeding grounds as well. A variety of gear was employed,
including harpoons, grapple hooks, baited and unbaited fish
hooks, and pound nets, trammel nets, weirs, stake row nets,
seines, and gill nets. Such gear was quite effective on thehighly susceptible sturgeons, and in relatively short periodsof time, usually 5-10 years, major stocks of sturgeons became substantially depleted.
Landings from the various sturgeon fisheries differedsomewhat, but the pattern of exploitation was always similar(Fig. 1). Landings increased rapidly over a relatively shortperiod during initial exploitation, then declined sharply andremained at low levels. Primary fishing emphasis was on
the Atlantic sturgeon (including the much smaller shortnose
sturgeon), the white sturgeon, and the lake sturgeon. Landings of Atlantic sturgeon peaked about 1890 with landingsof 3.3 million kg, but by the turn of the century all major
fisheries exhibited substantial declines or total collapse(Murawski and Pacheco 1977, Smith 1985). In 1892, a peak
production of about 2.5 million kg of white sturgeon wasrecorded from the Columbia River. However, by 1899 thefishery had collapsed and landings were only about 50,000

Freshwater; large turbid flowing
riversFreshwater; backwaters, sluggish
pools, bayous, oxbows of large
rivers and lakes

kg (Galbreath 1985). Similarly, landing of lake sturgeon
peaked around 1885 (2.3 million kg smoked flesh; 1,000 kegs
caviar; 1,400 kg isinglass) and then suffered a similar decline(Harkness and Dymond 1961). Commercial harvesting of
paddlefish became important after the lake sturgeon stocks
were depleted. By 1899, landings of paddlefish had increased
to 1.1 million kg from 0.47 million kg in 1894. Like theAcipenseridae, paddlefish landings decreased shortly afterlarge-scale exploitation began, but the decline was not as
precipitous nor as drastic as that of the other sturgeons(Gengerke 1986). In 1922, landings of paddlefish were still
0.63 million kg, and over the next 43 years landings ranged
from 0.27 million kg (1960) to 0.43 million kg (1975).

Current fisheries
Today, commercial harvesting of some North American
sturgeons still occurs; however, landings in the recreational
fishery often exceed commercial landings. The Atlantic
sturgeon has a broad geographical range, yet commercial
harvesting is currently restricted to Canada, New York,North Carolina, and Georgia, where only nominal landings
are reported (Smith 1985). Formerly, landings in South
Carolina were substantial relative to total U.S. landings, but
in recent years the fishery suffered major declines (Smithet al. 1984) resulting in an indefinite closure of the fishery.
All existing Atlantic sturgeon fisheries in the United Statesshould be closed to protect the remaining stocks. Harvestingof the sympatric shortnose sturgeon in the United States has
been banned since 1972 when it was listed as an endangered
species by the U.S. Fish and Wildlife Service (Miller 1972).
20

Landings of white sturgeon from the lower Columbia River(below the Bonneville Dam) in Washington and Oregon are
now at their highest level since the tum of the century. Most
commercial landings result from incidental capture in salmon
gillnets, although there is some focused fishing for sturgeon
in certain areas. Recreational hook-and-line fishing for whitesturgeon in the lower Columbia River has been increasing
steadily, and since 1977 recreational landings have exceeded
commercial landings. From 1977 to 1983, average commerciallandings have been 12,600 fish as compared with 27,300
fish for the recreational fisherman (Galbreath 1985). In termsof total number of fish caught, the landings in 1983 exceed
the recorded peak landings in 1892. However, individual fishweight has declined from a former average size of 68 kg toa present weight of 14-16 kg in the commercial fishery and
8 kg in the sport catch (Galbreath 1985). Continuing researchhas established that successful spawning is occurring below
Bonneville Dam, and the consensus is that the white sturgeon
stocks in the lower Columbia River below the Dam arehealthy. A combination of harvest regulations (minimum andmaximum size limits), increased food supplies, and a shorter
salmon gillnet fishing season are primarily responsible forthe good condition of the sturgeon stocks. Some harvestingof green sturgeon does occur in conjunction with the whitesturgeon, but their numbers are low and these fish are nothighly regarded as a food fish. In the upper Columbia River(above the Bonneville Dam), white sturgeon are essentiallylandlocked within each dammed river segment or pool.
Recruitment and stock size appears healthy in some areas,
but declines are occurring in others. Additional research isneeded to assess these various landlocked populations ofwhite sturgeon.
In California, commercial harvesting of white sturgeon has
been prohibited since 1917 but the sport fishery was reopened
in 1954. Up to 1963, sturgeon were taken incidentally tofishing for striped bass, Morone saxatilis. However, in 1964
angler success improved dramatically with the use of shrimp(Crangon spp., Palaemon macrodactylus) as bait (Kohlhorst1980). Since then, sturgeon have become the focus of an important sport fishery in the Sacramento-San Joaquin river
system. Population estimates suggest that abundance in thissystem decreased between 1967 and 1974, but abundancehas continually increased since then. These changes in
population size are believed to be due to variable recruitment rather than to fishing pressure. Currently, it is estimatedthat there are about 130,000 legal-sized adult white sturgeon
inhabiting this system, of which about 8 % are harvested annually (David Kohlhorst, Calif. Dep. Fish Game, Stockton,
CA, pers. commun., 29 Sept. 1986). No snag fishing isallowed in California and there is a minimum fish size of
102 cm (weight "'5.4-6.8 kg). Average size of the sport fish
landed is 13-18 kg. Catch records from sturgeon charter boats
indicate that between 1964 and 1983 the number of anglers/
year ranged from 1235 to 8284, and the number of fishcaught per year ranged from 320 to 2272 (David Kohlhorst
Calif. Dep. Fish Game, Stockton, CA, pers. commun., 29
Sept. 1986). Landings by charter-boat anglers represent

3A2

Atlantic Sturgeon(New Jersey fishery).....OJ~

ID

o.....

3

.....

B

CI)

~

Z

2

Lake Sturgeon(Lake Erie fishery)

5
zc(
...J

,

Z

ow
~

a:
~

3

CI)

c
2

White Sturgeon(Columbia River fishery)

1880

1890

1900

1910

1920

1930

YEAR
Figure 1
Commercial exploitation of various stocks of sturgeons. Data from(A) Murawski and Pacheco 1977, (8) Harkness and Dymond 1961, and(C) Galbreath 1985.

Similarly, the lake sturgeon is classified as rare over muchof its original range by the U.S. Fish and Wildlife Service.
However, this species does support a number of sport
fisheries, none of which exceeds that in Lake Winnebago,
Wisconsin (Folz and Meyers 1985). Harvesting of lake
sturgeon was prohibited from 1916 to 1931, but in 1932 aspear fishing season was established on Lake Winnebago.
Initially, spear fishermen were allowed to harvest 5 sturgeon
per season, with a minimum length of 76 cm TL, but current regulations are more restrictive with only one fish perseason of a I 14-cm minimum length allowed. Fishing success rate varies from 0.4 to 32.8% and averages 13.2%. During 1955-83, harvests ranged from 8 to 2235 fish (1982) (Folzand Meyers 1985). Based on harvest data and sampling of
spawning fish, it appears that the lake sturgeon stock in Lake
Winnebago has not declined since 1955 and that the population is stable or increasing.

21

Table 2
Growth, maturity and longevity of some North American sturgeons. These parameters can vary substantially according to latitude.

only a fraction of the sturgeon caught and recent total annual catch is estimated to be about 10,000 fish.
In Idaho, there are catch-and-release sport fisheries forwhite sturgeon in the Snake and Kootenai Rivers. However,recent findings suggest that possible closure of several sections of the Snake River may be needed because of estimatedlow population size (Cochnauer et al. 1985).
In contrast to most Acipenseridae, some populations of
paddlefish have actually increased substantially since the turnof the century, although other stocks no longer inhabit former
ranges (e.g., Canadian stocks). In the Mississippi, Missouri,
Ohio, and Red Rivers, paddlefish populations have significantly decreased while increased abundance has been reported from the Tennessee, Cumberland, and Arkansas
Rivers (Gengerke 1986). Sport fisheries, based almost exclusively on snag fishing, are permitted in 17 states and provide landings equal to about 70% of the commercial landings.
Annual harvest rates from sport and commercial fishing on
the order of 15-20% do not appear to damage most populations (Pasch and Alexander 1986).

on historic spawning rivers and widespread industrial pollution caused elimination or reduction in suitable sturgeon
habitat (Harkness and Dymond 1961, Leland 1968).

Fishery enhancement_

Early stock replenishment efforts
Near the end of the 19th century, fishery managers realizedthat the sturgeon fisheries had experienced substantial
declines and that something would have to be done to restore
the stocks if the fisheries were to be maintained. Unanimous
agreement was reached to rehabilitate the various stocks
through artificial propagation programs (Ryder 1890, Cobb
1900, Stone 1900). The first successful spawning ofa North
America sturgeon was accomplished on the Hudson River
in 1875 by Seth Green and Aaron Marks with the New YorkState Fish Commission. Working with Atlantic sturgeon
fishermen, eggs and milt were removed from ripe fish andartificially mixed. Using this approach, about 100,000 youngwere hatched over a two-week period. This early success
led to the mistaken belief that sturgeon propagation would
be an easy task. In 1888, the U.S. Fish Commission began
spawning activities with the Atlantic sturgeon on the Delaware River under the direction of J.A. Ryder (Ryder 1890).
Some limited successes occurred, but obtaining adequate
numbers of ripe females was a problem. Further, fungal infestation by Achlya and Saprolegnia often caused loss of the
incubating eggs. Subsequent workers attempting to spawn
Atlantic sturgeon encountered similar problems of limited
availability of ripe broodstock and fungal infections of eggs
(Dean 1894, Meehan 1909, Leach 1920). Early spawning
efforts with lake sturgeon also had limited success, although
5 million fry were produced in 1891 and released in the

Reasons for decline
As is evident from the landings data, sturgeons are highly
susceptible to man's activities, despite their large size andextended life span (Table 2). Sturgeons mature at an advancedage (8-25 years), demonstrate protracted spawning periodicities (2-8 years), and inhabit areas of concommitant use
by man (rivers, lakes, estuaries, coastal environments). Consequently, major population perturbations can be easily effected by man. In all cases, major stocks of sturgeons were
overexploited by fishing (Harkness and Dymond 1961,
Priegel and Wirth 1977, Galbreath 1985, Pasch and Alexander 1986, Smith 1985). Additionally, installation of dams
22

niques for all species are still in the "art" stage rather thanbeing a science, and success is highly dependent upon thecondition and stage of ripeness of wild-caught broodstock.
Of the above species, collection of Atlantic sturgeon broodstock is the most difficult as population numbers are low andspawning areas are poorly known and occur in deep areasof fast moving waters. Further, Atlantic sturgeon do not feed
during their spawning migration and thus are not susceptible to hook-and-line capture. Consequently, only limited
spawning and culture success has been obtained with Atlantic sturgeon despite substantial efforts undertaken in South
Carolina (Smith et al. 1981, Smith and Dingley 1984). In
contrast, lake sturgeon can be routinely observed in the actof spawning in areas where the current is upwelling andwhere large rocks, boulders, and broken slabs of concrete
have been riprapped at a steep angle into the water (Priegel
and Wirth 1977). Spawning females are dip-netted, and thefree-flowing eggs are removed through a small incision. The
female is sutured and returned to the water. Similarly, running ripe males can be dip-netted and their milt stripped byabdominal compression and used to fertilize the eggs
(Czeskleba et al. 1985). Ripe white sturgeon are captured
primarily by baited hook-and-line as they move into spawning areas in the Sacramento River. These fish are induced
to spawn using hormonal injection (usually commerciallyavailable carp pituitaries). Additionally, success has beenobtained in using selected prespawning white sturgeon collected in San Francisco Bay in the fall. Final maturation was
induced in the spring and the fish were successfully spawned(Doroshov et al. 1983). Shortnose sturgeon are listed as anendangered species in the United States; therefore, a federal
permit is required to collect them. In South Carolina, mature
migrating broodstock are obtained from commercial shadfishermen as incidental catch in their gill nets. Like the whitesturgeon, these fish can be induced to spawn by injectionof fish pituitaries (Smith et al. 1985). Paddlefish are captured with gill nets within I-I V2 months of their normal
spawning time and held in hatchery tanks. They are induced
to ovulate using paddlefish pituitary glands, although recent
work with LH-RHa suggests that this hormone may be an
excellent substitute (Graham et al. 1986).
Techniques for fertilization and incubation of eggs are
generally similar among the sturgeons. Eggs are removed
from white sturgeon and lake sturgeon through an abdominal
incision over a short period of time. In contrast, eggs are
stripped from shortnose sturgeon and paddlefish at 20-60
minute intervals over a long period of time. Sperm is collected from the males with a syringe and usually diluted withwater (1 :200) just prior to fertilization to prevent polyspermy.
Eggs and sperm are mixed for about 5 minutes and then asilt, mud, or clay suspension is added to inhibit adhesion of
the eggs. Also, chemical treatments have recently beendeveloped to eliminate the adhesiveness (Kowtal et al. 1986).
The non-adhesive eggs are incubated in McDonald incubators(jars) for about 5-7 days at a temperature of 14-16°C. During incubation, eggs are gently rolled with upflow water.
Upon hatching, the sac-fry swim up and out of the incubators

Detroit River by the Ohio Game and Fish Commission. Efforts continued, but successes were limited to instances inwhich running ripe females containing ovulated eggs were
captured at the same time as ripe males (Harkness and Dymond 1961). Unfortunately, such instances were uncommon.
During 1906-09, efforts were initiated to spawn the muchsmaller shortnose sturgeon. This work was conducted at theTorresdale Hatchery in Philadelphia where ponds were usedin an attempt to naturally ripen captive adult shortnose
sturgeon (Meehan 1909). In several instances, females expelling eggs were removed from the ponds and small
numbers of fry were hatched. As before, acquisition ofsimultaneously ripe males and females was a problem.
In spite of the high level of interest, efforts to propagate
sturgeons in the United States were abandoned by 1912. A
short time later, Canadian workers initiated culture efforts
but they also experienced the same problems as previously
noted. About 1920, they discontinued their propagation
efforts.

Soviet propagation efforts
The demonstration that secretions of the pituitary gland could
be used to induce final ripening of fish gonads (Atz andPickford 1959) led to renewed interest in sturgeon propagation, especially in the Soviet Union where overfishing andinstallation of dams had caused declines in sturgeon populations similar to those in North America. Beginning in theearly 1960s, a major propagation effort was initiated in theSoviet Union based on the use of extracted sturgeon pituitary
glands to induce spawning of ripe sturgeons (Manea 1969).
Annual production of stockable-size fingerling (1-3 g) is now
approximately 60-100 million fish. Sturgeon fingerlings arestocked in river deltas during the summer and recaptured as
sexually mature adults after 10-20 years of grow-out in thesea (Doroshov and Binkowski 1985). No sea fishing forsturgeon is allowed, and caviar is the main product of thissea ranching approach. Based on a survival rate of only
1-3 %, the annual sturgeon landings in the late 1970s fromthe Caspian Sea basin was 26,000 mt (metric tons), which
resulted in the production of 1750 mt of caviar (Doroshov
and Binkowski 1985).

Current North American culture efforts
During the past 10 years, there has been renewed interestin the culture of North American sturgeons. Information on
the life history and ecology of the various species, coupledwith the use of hormones, has resulted in the spawning of
Atlantic sturgeon (Smith et al. 1980), shortnose sturgeon(Buckley and Kynard 1981, Smith et al. 1985), lake sturgeon(Avelallemant et al. 1983, Folz et al. 1983, Czeskleba et al.
1985), and white sturgeon (Doroshov et al. 1983). Techniques for spawning and rearing paddlefish were developedin the mid-1960s and early 1970s, and recently there havebeen efforts to rear this species for stocking purposes andfor caviar production (Graham et al. 1986). Spawning tech23

and are collected in adjacent tanks. After about 10 days, thefry begin feeding.
Larval and juvenile rearing differs among the various
sturgeons. White and shortnose sturgeon can be trained toaccept soft-moist and dry diets and are typically reared intanks in intensive systems. Survival rate to a small juvenile
size (f\J30 g, 3-4 months old) is about 15 %. After this size
is attained, mortality rarely occurs. Rearing of larval andjuvenile lake sturgeon has been difficult because they appear
to require live foods (Anderson 1984, Czeskleba et al. 1985,
Graham 1986a) and attempts to rear this species in fertilized
ponds has resulted in poor survival. Thus, it is costly to produce large numbers of juvenile lake sturgeon. Paddlefish
juveniles have been reared both extensively in ponds andintensively in tanks (Graham et al. 1986). In the extensive
approach, ponds are fertilized to induce a dense zooplankton
population which serves as food for paddlefish. Ponds areusually stocked when fry are 5 days old and at a density of
49,400 fish/ha. Average survival is 35% and growth is rapid.
At the end of a 140-day growing season, most paddlefish
are about 250-300 mm in length. In the intensive systems,
larvae are initially reared on zooplankton (primarily Daphnia)
and then trained to accept soft-moist and dry formulated
feeds. Unfortunately, feeding is not efficient because paddlefish do not actively seek feed and they cannot be reared undercrowded conditions. Although the intensive approach is successful, it requires a large amount of hatchery space.

Stock enhancement programs

stocking programs with this species. During 1986, only 26
adult Atlantic sturgeon were captured during an 8-week intensive fishing effort by ex-commercial sturgeon fishermen.
Of these, no males were running ripe and no females could
be induced to ovulate. In contrast to Atlantic sturgeon, significant progress has been attained in spawning and cultureof shortnose sturgeon. Basic spawning techniques have beendeveloped and fry have been produced during 1984-86.
Grow-out ofjuveniles in intensive systems has been successful (Smith et al. 1986), and some fish have attained a maturesize (1.8-2.1 kg) after only 18 months of culture. Thus,
development of domesticated broodstock for the species appears promising. In 1985-86, a total of 6600 juveniles werereleased in South Carolina waters, of which 541 were 35
cm in size and were tagged. Preliminary capture data suggest these fish are surviving and growing in the wild, but
a number of basic questions need to be addressed. Amongthese are questions concerning homing behavior, optimum
size of juveniles for release, and size of natural populations.
Studies are underway in South Carolina to examine these andother questions which will help determine the feasibility ofstock replenishment programs with shortnose sturgeon.
There has been interest in stocking programs with the lake
sturgeon in several areas of former abundance. The Menominee River, which forms a boundary between the upper
peninsula of Michigan and northeastern Wisconsin, has
several dammed sections that support fishable populationsof lake sturgeon. In 1982, 290 large juveniles (18 cm) andin 1983, 11,000 small juveniles (30 mm) were stocked in
the Sturgeon Falls section of the Menominee River, a site
uninhabited by sturgeons in recent years (Thuemler 1985).
The area appeared suitable as sturgeon habitat, but subsequent sampling efforts and radio telemetry studies indicatedthat the stocked fish moved out of that section of the river(Dan Folz, Wisc. Dep. Nat. Resourc., Oshkosh, WI, pers.
commun., 18 June 1986). There is speculation that the Lake
Winnebago strain of fish used to stock this area did notpossess the needed behavioral characteristics of the "riverrace" of lake sturgeon that inhabit the Menominee River.
At present, the Lake Winnebago population oflake sturgeon
is stable or increasing, and additional spawning sites are being
documented in the Wolf River resulting from installation of
additional riprapping of the shoreline accompanying increased development. Thus, Wisconsin's main focus is torefine culture techniques in anticipation of future need
(AveLallemant et al. 1983) and to continue to intensively
manage the existing population in Lake Winnebago to maintain a sustained yield (Folz and Meyers 1985). However,there are 4-6 locations in Wisconsin formerly containing
sturgeon populations that appear to be environmentally suitedfor restocking. Proposed restocking protocol suggest that 3
years of consecutive stocking should be undertaken using fry,fingerlings, and adults from the same river systems, ifpossible, to preserve the genetic integrity of the stocks.
In Missouri, initial efforts are underway to implement alake sturgeon reintroduction plan (Graham 1984). Lake
sturgeon were once abundant in Missouri, but now there are_

Although substantial progress has been achieved in rearing
some of the more important North American sturgeons, efforts to enhance and/or reestablish fisheries are relatively
small scale. The culture technology for white sturgeon is by
far the most developed. There are a number of aquaculture
operations in California growing this species as a food fish
(Ken Beer, The Fishery, Galt, CA, pers. commun., 2 Oct.
1986). Further, development of cultured broodstock has progressed well. At the University of California, Davis, 2 Jh-3
year-old cultured males have been successfully used to fertilize eggs from wild-caught females (Serge Doroshov, Univ.
Calif., Davis, CA, pers. commun., 17 June 1986). Further,5-year-old females are beginning to show signs of maturation. Commercial sturgeon farmers in California now
routinely use cultured males and are rearing females in hopesof eliminating their dependency on wild fish. In spite of thiswell-developed hatchery technology, there currently are noplans for stocks enhancement programs for white sturgeon,
because fishery managers feel that most stocks are stable orincreasing. However, the sturgeon farmers are required bytheir collecting permits to restock sevral thousand sac-fry
per wild sturgeon used for spawning purposes.
On the Atlantic coast, there is substantial interest in establishing stocking programs for the Atlantic and shortnose
sturgeons. However, difficulties in capture of Atlantic sturgeon broodstock has thus far prevented initiaion of any

24Conclusions

only isolated reports of occasional individuals being caught
in the Missouri and Mississippi rivers. Graham (1984)
evaluated the characteristics of the various state waters andhas identified numerous rivers, lakes, and reservoirs that appear suitable for restocking of lake sturgeon. To test thefeasibility of the restocking plan, Mark Twain Lake in northeastern Missouri was stocked in 1984 with 11,800 culture
fingerlings originating from Lake Winnebago sturgeon(Graham 1986a). This new reservoir was selected because
it contained abundant natural food, few predators, and turbid water. Additionally, a main tributary appeared to offer
suitable spawning conditions. No sampling of the 7900-hareservoir has been attempted, but one fish was reported captured in early summer 1986. During the fall 1986, an additional 10,750 fingerlings <,"'200 mm in size) were stocked
into this reservoir to complete the stocking program. Reintroduction success will be evaluated over time, and, depending on the results of this stocking program, other waters in
Missouri may be similarly stocked. The feasibility of restocking lake sturgeon in selected waters in Minnesota is also
under examination.
Several midwestern states have considered stocking paddlefish, but lack of a dependable supply of fingerlings hasdelayed stocking efforts. However, from 1970 to 1977,
paddlefish were stocked in Table Rock Lake, a 17,500-halake in southwestern Missouri previously uninhabited by thisspecies (Graham 1986b). Paddlefish fry (6-8 mm) were
stocked in 1970, but population analyses suggest that thesefish did not survive. Between 1972 and 1977, 82,600(250-300 mm) fingerlings were stocked and these fish
appeared to have an excellent survival rate. Growth of theintroduced fish has been rapid and there was evidence of
spawning in 1983. As a result of this stocking program, an
expanding sport fishery (by snagging) has developed, with
2970 fish caught during 1983-84. In 1984, the estimatedfishery landings were 18,000 kg, the most successful paddlefish stocking program to date. Missouri is stocking fingerlings in Lake of the Ozarks to maintain a fishery and also
into Harry S. Truman Reservoir in an attempt to establish
a population. In 1983, Alabama stocked a 104-ha lake with
440 fish (0.5 kg in size) in the hopes of eventually harvesting these fish for food. Additionally, the Kansas Game andFish Commission stocked about 5000 paddlefish juveniles(10-50 cm) into the 3600-ha John Redmon Reservoir in an
attempt to establish a population (Graham 1986b). Besides
the interest to establish fisheries through stocking programs,
there is also interest in culturing paddlefish as an aquaculture
species (Semmens and Shelton 1986). However, development of aquaculture technology for this species is still in the
preliminary stage.

_

Significant progress has been achieved in recent years inpropagating various North American sturgeons. In somecases, culture technology is sufficiently advanced to provide
the basis for development of an aquaculture industry (e.g.,
white sturgeon; Marx 1986). However, for the most part,stock enhancement or reintroduction programs are still in
the conceptual or preliminary stocking-assessment phase formost species. In many instances, availability of suitable quantities of stockable juveniles is the problem, while in othercases the sturgeon resources have been so depleted that state
management agencies have prior commitments to maintainexisting fisheries and, therefore, are unwilling to commit theresources needed to develop stock enhancement programs.
Sturgeon populations cross many state boundaries and historically they covered broad expanses of North America.
Thus, it is proposed that cooperative state-federal programs
be jointly sponsored, perhaps through regional agreements.
To a certain degree, the present progress achieved in cultureof North American sturgeons (e.g., white, shortnose, lake)
is in part attributable to support from various federal agencies (e.g., U.S. Fish and Wildlife Service, Sea Grant Officeof the Department of Commerce). Since sturgeon mature andspawn at an advanced age, a long-term commitment by thevarious states and federal agencies will be required to properly evaluate the potential for stugeon restoration efforts. Unfortunately, such commitment does not appear likely fromany governmental entity at present. For the foreseeable
future, stock enhancement programs will continue on amodest scale. Planning and recommendations for stocking
programs and their evaluation as proposed by the states ofMissouri and Wisconsin are commendable and should serveas an example to other states and agencies. With proper
foresight, the programs underway today could well resultin a higher level of interest and activity by fishery managers
in the future.

Citations/_

Anderson, E.R.
1984 Artificial propagation of lake sturgeon Acipenser fulvescens(Rafinesque) under hatchery conditions in Michigan. Mich. Dep.
Nat. Resourc., Fish. Res. Rep. 1898, 32 p.
Atz, J.W., and G. Pickford
1959 The use of pituitary hormones in fish culture. Endeavour (Eng!.
cd.) 18: 127.

AveLallemant, S., D. Czeskleba, and T. Thuemler
1983 Artificial spawning and rearing of the lake sturgeon at the Wild
Rose State Fish Hatchery, Wisconsin. Wise. Dep. Nat. Resourc.,
Fish Culture Note 5, 7 p.
Boscbung, H.T., Jr., J.D. Williams, D.W. Gotsball, D.K. Caldwell,and M.C. Caldwell1983 The Audubon Society field guide to North American fishes,
whales and dolphins. A.A. Knopf Inc., NY, 848 p.
Buckley, J., and B. Kynard
1981 Spawning and rearing of shortnose sturgeon from the Connecticut River. Prog. Fish. Cult. 43(2):74-76.

25

Cobb, J.N.
1900 The sturgeon fishery of Delaware River and Bay. Rep. U.S.
Comm. Fish Fish. for 1899, Pt. 25, p. 369-380.
Cochnauer, T.G., J.R. Luckens, and F.E. Partridge
1985 Status of white sturgeon, Acipenser transmontanus, in Idaho.
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sturgeons: Biology and aquaculture potential, p. 127-134. Dr W.
Junk Publ., Netherlands.
Czeskleba, D.G., S. AveLallemant, and T.F. Thuemler
1985 Artificial spawning and rearing of lake sturgeon, Acipenser
fulvescens, in Wild Rose State Fish Hatchery, Wisconsin, 1982-1983.
Environ. BioI. fish. 14(1):79-86.
Dadswell, M.J.
1979 Biology and population characteristics of the shortnose sturgeon,
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Dean, D.
1894 Recent experiments in sturgeon hatching on the Delaware River.
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1985 Epilogue: A perspective on sturgeon culture. In Binkowski, F.P.,
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Doroshov, S.I., W.H. Clark, Jr., P.B. Lutes, R.L. Swallow, K.E. Beer,
A.B. McGuire, and M.D. Cochran1983 Artificial propagation of the white sturgeon, Acipenser transmontanus Richardson. Aquaculture 32:93-104.
Folz, D.J., and L.S. Meyers
1985 Management of the lake sturgeon, Acipenser fulvescens, population in the Lake Winnebago system, Wisconsin. In Binkowski, F.P.,
and S.l. Doroshov (eds.), North American sturgeons: Biology andaquaculture potential, p. 135-146. Dr W. Junk Publ., Netherlands.
Folz, D.J., D.G. Czeskleba, and T.F. Thuemler
1983 Artificial spawning of lake sturgeon in Wisconsin. Prog. FishCult. 45(4):231-233.
Galbreath, J.L.
1979 Columbia River colossus - the white sturgeon. Oregon Wild I.
34:3-8.
1985 Status, life history, and management of Columbia River whitesturgeon, Acipenser transmontanus. In Binkowski, F.P., and S.l.
Doroshov (eds.), North American sturgeons: Biology and aquaculture
potential. p. 119-126. Dr W. Junk Publ., Netherlands.
Gengerke, T.W.
1986 Distribution and abundance of paddlefish in the United States.
In Dillard, J., et al. (eds.), The paddlefish: Status, management andpropagation, p. 22-35. North Central Div., Am. Fish. Soc., Spec.
Publ. 7.
Graham, K.
1984 Missouri's lake sturgeon reintroduction plan. Missouri Dep.
Conserv., Columbia, MO, 11 p.
Graham, L.K.
1986a Reintroduction of lake sturgeon into Missouri. Final Rep.,
DJ. Proj. F-I-R-35, Study S-35. Missouri Dep. Conserv., Columbia, MO, 11 p.
1986b Establishing and maintining paddlefish populations by stocking.In Dillard, J., et al. (eds.), The paddlefish: Status, management
and propagation, p. 95-105. North Central Div., Am. Fish. Soc.,
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Graham, L.K., E.J. Hamilton, T.R. Russell, and C.E. Hicks
1986 The culture of paddlefish - a review of methods. In Dillard, J.,et al. (eds.), The paddlefish: Status, management and propagation,
p. 78-94. North Central Div., Am. Fish. Soc., Spec. Publ. 7.
Harkness, W.J.K., and J.R. Dymond
1961 The lake sturgeon, the history of its fishery and problens ofconservation. Ontario Dep. Lands Forests, Toronto, 121 p.

Kohlhorst, D.W.
1980 Recent trends in the white sturgeon population in California's
Sacramento-San Joaquin estuary. Calif. Fish Game 66(4):210-219.
Kowtal, G.V., W.H. Clark, Jr., and G.N. Cherr
1986 Elimination of the adhesiveness in eggs from the white sturgeon,
Acipenser transmontanus: Chemical treatment of fertilized eggs.
Aquaculture 55(2): 139-144.
Leach, G.C.
1920 Artificial propagation of sturgeon, review of sturgeon culturein the United States. Rep. U.S. Fish. Comm. 1919:3-5.
Leland, J.G. HI
1968 A survey of the sturgeon fishery of South Carolina. Contrib.
Bears Bluff Lab. 47:1-27.
Magnin, E.
1964 Croissance en longeur de trois esturgeons d' Amerique du Nord:
Acipenser oxythynchus Mitchill, Acipenser fulvescens Raffiensque,et Acipenser brevirostris LeSueur. Int. Ver. Theor. Angew. Limnol.
Verh. 15:968-974.
Manea, G.
1969 Methods for artificial spawning of sturgeons (Acipenseridae) andhatching of fry. Riv. Ital. Piscicoltura ittiopatologia 4(4):81-86.
Marx, W.
1986 Life at the bottom makes the sturgeon a tough customer. Smithsonian 17(5):82-93.
Meehan, W.E.
1909 Experiments in sturgeon culture. Trans. Am. Fish. Soc. 39:
85-91.
Miller, R.R.
1972 Threatened freshwater fishes of the United States. Trans. Am.
Fish. Soc. 101 :239-252.
Murawski, S.A., and A.L. Pacheco
1977 Biological and fisheries data on Atlantic sturgeon, Acipenser oxyrhynchus. Tech. Ser. Rep. 10, Sandy Hook Lab., Natl. Mar. Fish.
Serv., NOAA, Highlands, NJ, 69 p.
Pasch, R.W., and C.M. Alexander
1986 Effects of commercial fishing on paddlefish populations. In
Dillard, J., et al. (eds.), The paddlefish: Status, management andpropagation, p. 46-53. North Central Div., Am. Fish. Soc., Spec.
Publ. 7.
Priegel, G.R., and T.L. Wirth
1977 The lake sturgeon: Its life history, ecology and management.
Wise. Dep. Nat. Resourc., Publ. 4-3600(77), 20 p.
Russell, T.R.
1986 Biology and life history of the paddlefish - A review. In Dillard,J., et al. (eds.), The paddlefish: Status, management and propagation, p. 2-21. North Central Div., Am. Fish. Soc., Spec. Publ. 7.
Ryder, J.A.
1890 The sturgeon and sturgeon industries of the eastern coast of theUnited States, with an account of experiments bearing upon sturgeon
culture. U.S. Fish Comm., Bull. (1888)8:231-238.
Semmens, K.S., and W.L. Shelton
1986 Opportunities in paddlefish aquaculture. In Dillard, J., et al.
(eds.), The paddlefish: Status, management and propagation, p. 106113. North Central Div., Am. Fish. Soc., Spec. Publ. 7.
Scott, W.B., and E.J. Crossman
1973 Freshwater fishes of Canada. Fish. Res. Board Can., Bull. 184,966 p.
Smith, T.I.J.
1985 The fishery, biology, and management of Atlantic sturgeon,
Acipenser oxyrhynchus, in North America. Environ. BioI. Fish
14(1):61-75.
Smith, T.I.J., and E.K. Dingley
1984 Review of biology and culture of Atlantic (Acipenser oxyrhynchus) and shortnose sturgeon (A. brevirostrum). J. World Maricult.
Soc. 15:210-218.

26

Smith, T.I.J., E.K. Dingley, and D.E. Marchette1980 Induced spawning and culture of Atlantic sturgeon. Prog. Fish.
Cult. 42:147-151.
1981 Culture trials with Atlantic sturgeon, Acipenser oxyrhynchus in
the U.S.A. J. World Maricult. Soc. 12:78-87.
Smith, T.I.J., D.E. Marchette, and R.A. Smiley
1982 Life history, ecology, culture and management of Atlantic
sturgeon. Acipenser oxyrhynchus oxyrhynchus Mitchill, in South
Carolina. S.C. Wild!. Mar. Resour. Res. Dep., Final Rep. to U.S.
Fish Wildl. Serv., Proj. AFS-9, 75 p.
Smith, T.I.J., D.E. Marchette, and G.F. Ulrich
1984 The Atlantic sturgeon fishery in South Carolina. N. Am. J.
Fish. Manage. 4: 164-176.
Smith, T.I.J., E.K. Dingley, R.D. Lindsey, S.B. Vansant, R.A. Smiley,
A.D. Stokes
1985 Spawning and culture of shortnose sturgeon, Acipenser brevirostrum. J. World Maricult. Soc. 16:104-113.
Smith, T.I.J., W.E. Jenkins, W.O. Oldland, and R.D. Hamilton
1986 Development of nursery systems for shortnose sturgeon, Acipenser brevirostrum. Proc. Annu. Conf. Southeast. Assoc. Fish
Wildl. Agencies 40: 169-177.
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1900 The spawning habits of the lake sturgeon (Acipenser rubincundus). Trans. Am. Fish. Soc. 29:118-128.
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1980 Reproduction of shortnose sturgeon (Acipenser brevirostrum)in the Holyoke Pool of the Connecticut River, Massachusetts. Copeia
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Thuemler, T.F.
1985 The lake sturgeon. Acipenser fulvescens, in the Menominee
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27

Application of
Yield-per-Recruit andSurplus Production Models
to Fishery Enhancement
Through Juvenile Releases

The release of hatchery-reared juveniles to enhance fisheries
for a number of species is practiced in Japan and to a lesser
degree in other countries, including the United States andNorway (Yatsuyanagi 1982, Botsford and Hobbs 1984,
Isibasi 1984, Ulltang 1984). When juveniles are released toaugment a natural stock that is the basis of an existing fishery,stocking combines extensive mariculture with traditional
fishery science. New quantitative tools are needed to evaluate
and manage this system. The simple stocking vs. harvestingratios that are used to evaluate and manage aquaculture nolonger apply in the presence of varying fishing pressure anda natural stock. For example, fishing mortality often increases
as stocking levels increase, making it difficult to attribute
any increase in yield solely to the increase in stocking. However, traditional fishery production models are also inadequate since they do not incorporate stocking as a variable.
Although some models have been developed to examine theeffects of stocking relative to hatchery cost and the returnto the fishery, these analyses have not taken into accountother management variables including size limits and fishingeffort (e.g., Oshima 1984). More sophisticated models havebeen developed which can be used to simulate the effectsof stocking or develop optimal fishery policy, and ?an beapplied in situations where the biology of the resource is wellknown and estimates of age-specific population parameters
are available (Watanabe et al. 1982, Botsford and Hobbs
1984, Ulltang 1984, Watanabe 1985).
In this paper the traditional Beverton and Holt (1957) yieldper-recruit model and the nonequilibrium Ricker surplus production model (Ludwig and Walters 1985), both standard
tools for fishery management, will be modified so that they
can be applied to evaluate and manage fisheries in which
juveniles are released. The yield-per-recruit model can beapplied with very little modification to juvenile releases toevaluate the yield-per-released-juvenile as a function of thebiological parameters (growth and mortality) and management parameters (release size, size at entry, and fishing mortality). The contribution of the released juveniles to thespawning stock can be evaluated in a similar fashion by computing the spawning-stock biomass per released juvenile. The
Ricker surplus production model can be modified to express
the catch as a function of effort and stocking so that a timeseries of stocking, catch, and effort data can be analyzed toevaluate the effectiveness of stocking and to estimate maximum sustainable yield in the presence of juvenile releases.

JEFFREY J. POLOVINA
Honolulu Laboratory
Southwest Fisheries Center
National Marine FisherifjJ Service, NOAA
Honolulu, Hawaii 96822-2396

ABSTRACT
Yield-per-recruit and surplus production models are modified
for use when hatchery-reared juveniles are released into afishery. The yield-per-recruit model indicates that species withlow ratios of natural mortality to growth and high asymptotic
weight offer the greatest potential weight yield per stockedjuvenile. The Ricker surplus production model is easily modified to express catches as functions of fIShing effort and numbersof juveniles released. Thus the model can be used to estimate
the effectiveness of stocking a fishery with hatchery releases
based on a time series of catch, stocking, and effort data. The
model can also be used as a simulation tool.

Yield-per-recruit models_

The Beverton and Holt (1957) yield equation can be formulated as a function of the ratio of instantaneous mortality
to von Bertalanffy growth (M/K), the ratio of length atrecruitment to the fishery to asymptotic length (c), the ratioof fishing mortality to natural mortality (F/M), and the ratioof length of the stocked juvenile to the asymptotic length (a).
29

0.20
0.25

1.0

....8

>-Q;

~_------0.3

.r:
(f)

~

W

>-CD .8

0.40

u:::
2 .6
C

....8

.8

.r:
(f)

_ _-0.5

1.0

0.30

.4

0.40

u:::

0.30

2
~

0.25

Cii
.r:

~_----0.15

.6

c

0.20

_----.05

W .4

0, .2

Cii

....

.r:

c

OJ

0,.2
c

0.5

1.0

1.5

2.0

2.5

3.0

3.5

OJ
...J

4.0

Fishing Mortality/Natural Mortality

o

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Fishing Mortality/Natural Mortality

Figure 1
Yield per stocked juvenile for Pristipomoides filamentosus as functionof relative length of entry and relative fishing mortality. Estimates of
MIK=1.7, W==8.5 kg taken from Ralston (1981); size of releasetaken as 0.1 L=.

Figure 2
Spawning-stock biomass (kg) per stocked juvenile for Pristipomoides
filamentosus as function of relative length of entry and relative fishingmortality. Estimates of MIK = 1.7, W= = 8.5 kg taken from Ralston(1981); size of onset of sexual maturity taken as 0.5 L oo ; size of release
set at 0.1 L oo 'Under this formulation the yield (Y) per stocked juveniles(S) is:population spawning-stock biomass to a given level. The
SSB/S and Y/S equations, together with the hatchery costs
and the value of the harvested fish, can serve to evaluate theeconomic benefits of the release programs as functions ofvariables c, a, M/K, and F/M.
Hatchery technology and knowledge of the early-life
history of marine organisms have made it possible to rear
numerous marine organisms. The Y/S and SSB/S equations
permit comparisons of the benefits from stocking among
species with different population parameters. For example,
there are three commercially important species in Hawaii thatmight be candidates for hatchery release programs: Mahimahi, Coryphaena hippurus; a snapper, P. filamentosus; anda spiny lobster, Panulirus I1Ulrginatus. The Y/ S isopleths werecomputed for each of these species, and the maximum valuesof Y/S, for all c, as a function of F/M, were determined.
These maximum values of Y/ S are plotted for the three
species (Fig. 3). The differences between the three species
in their contribution to the fishery are striking. For example, when fishing mortality is equal to natural mortality andthe size at entry to the fishery is optimal, a released spiny
lobster will contribute 0.02 kg to the fishery, a released snapper will contribute 0.3 kg, and a released mahimahi will contribute an amazing 2.5 kg. Even when price per kilogram
is considered and the possibility that only 25-50% of adultmahimahi remain around the islands, the mahimahi releases
appear to offer high economic return. The contribution ofa released mahimahi to the fishery is so much greater thanthat of the snapper, and in turn the contribution of a snapperis greater than that of the spiny lobster, largely because ofdifferences in the M/K ratio (1.0 for mahimahi, 1.7 for snapper, and 3.0 for lobster) and the asymptotic weight (30 kg
for mahimahi, 8.5 kg f::lr snapper, and 1.7 kg for spiny
lobster). The lower the ratio of natural mortality to growth, .
the greater the survival of the released individual; and the

Y/S=(M/K) (F/M)«1 - c)/(1 - a))(M/Kl(l/ (M/K + (F/M) (M/K))-3(1-c)/(1 + (M/K) + (F/M)(M/K))+ 3(1 - c)2/(2 + (M/K) + (M/K)(F/M))- (1 - c)3/(3 + (M/K) + (F/M)(M/K)).
In a similar fashion, the spawning-stock biomass can be expressed as a function of the same variables plus the ratio of
the length at onset of sexual maturity to the asymptotic length(Beddington and Cooke 1983).
Based on these formulations, just as in the traditional yieldper-recruit analysis, the yield-per-stocked juvenile (Y/S) andthe contribution of the stocked juvenile to the spawning stock
biomass (SSB/ S) can be calculated as functions of F/ M andc (Figs. 1,2). The value of the yield per stocked juvenile
varies considerably with c and F/M, so the proper choiceof F/M and c is necessary to maximize the benefit from stocking. For example, in Figure 1, when the length of entry to
the fishery is 50% of the asymptotic length, a hatcheryreleased juvenile opakapaka, Pristipomoides filamentosus,
contributes 0.3 kg to the fishery when fishing mortality equals
natural mortality; whereas when fishing mortality increases
to 1.5 natural mortality, at the same size of entry, the contribution to the fishery of a hatchery-released juvenile opakapaka will increase 33 % to 0.4 kg. The SSB/S isopleths
indicate the contribution of a stocked juvenile to the population spawning-stock biomass. For example, for the snapper(opakapaka) when F/M = 1.5 and c = 0.5, a stocked juvenile
will contribute 0.15 kg to the population spawning-stock
biomass (Fig. 2). If the spawning-stock biomass of the
population is known, the SSB/S equation can estimate thenumber of juveniles needed to be released to increase the30

To modify these equations to include HI hatchery-released
juveniles in year t before harvesting, it is necessary to express
the biomass in year t + 1 resulting from HI' A power function relationship_ _- - - - Mahlmahl

3.0

Q)

~2.5
Q)

>
::J
--,
,,2.0
Q)

.x
c.>

with parameters a and b appears appropriate for hatcheryreleases of Oregon coho salmon (Peterman and Routledge1983). For a fast-growing species the major contribution
from stocking to the fishable biomass will occur in the same
year as the stocking, and thus Ht+l rather than HI would be
used in the power function equation.
If the biomass from the hatchery-released stock is simply
added to that of the natural stock in the first equation of the
Ricker model for surplus production, then we obtain:oU5 1.5
Q;
Q.

0,1.
~

:g
~ .5

_ - - - - - - - - - Opakapaka

~
o

0.5

Spi ny Lobster

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Fishing Mortality/Natural Mortality

Figure 3
Maximum yield per stocked juvenile as a function of relative fishingmortality for mahimahi, opakapaka, and spiny lobster. Parameter estimates for mahimahi M/K = 1.0, W = 30 kg (Uchiyama et a!. 1986); foropakapaka M/K = 1.7, W = 8.5 kg (Ralston 1981); for spiny lobster
M/K = 3.0, W = 1.7 kg (Polovina uaJJ bl. data).

This modified equation, together with the two other equations of the Ricker model, produces a production model
which incorporates hatchery releases. The contribution of
the hatchery releases will increase the catch directly throughEquation (3) and those that are not caught will increase SI
through Equation (2).
The Ricker surplus model without stocking shows the usual
dome shape in which production first increases then decreases
ultimately to zero with increasing fishing mortality (Fig. 4).
When a fixed number of hatchery releases are added to thesystem, the yield curve has the usual dome shape as a function of fishing mortality; but rather than declining to zero,
as is the case of an unstocked population, the yield approaches
an asymptotic yield of a(HI)b with increasing fishing mortality (Fig. 4). The relative contribution of the releases tothe fishery will be greatest for relatively high levels of fishingmortality. Hatchery releases can increase the maximum yieldand the corresponding level of optimum fishing effort.
If hatchery releases occur in the absence of a natural
population the Ricker model with stocking just reduces one
equation:greater the asymptotic weight, the greater the weight gainedby the released individual. The SSB/S follows the same orderfor the three species as Y/S. Thus among the candidates forjuvenile release, those with low M/K ratios and high asymptotic weights will offer the greatest contribution in biomass
to the fishery.

Fishery production models
with stocking_

The most frequently used production models, Schaefer andGulland-Fox, do not explicitly specify a recruitment relationship, and hence do not easily lend themselves to modification to include hatchery releases. However, the Ricker model
for surplus production (Ludwig and Hilborn 1983) is a simple production model which can easily handle stocking. The
Ricker model for surplus production is expressed by thefollowing three equations (Ludwig and Walters 1985):

Unfortunately, due to the nonlinear nature of the Ricker
surplus production model, it is not as easy to estimate theparameters as, for example, for the Schaefer model. A complete approach to parameter estimation for the Ricker modelis presented in Ludwig and Hilborn (1983). Here a simplified
approach will be presented for the Ricker model with stocking when it is assumed that the fishing effort is measured
without error. First, assume a value for q and compute B,
and CI from Equations (2) and (3). Then estimate A, B, a,and b from Equation (4) with the nonlinear regression, using
the B's and S's obtained from the previous step. Finally,vary q and repeat the previous steps until the sums of squaresof the nonlinear regression are minimized. Computer programs for nonlinear regression can typically be used as a basis
for this parameter estimation approach.

(1)

(2)
(3)

where B I is the population biomass in year t, SI is thebiomass remaining after harvest in year t, CI represents thecatch in year t, £1 denotes the effort in year t, VI represents
independent normally distributed random variables with meano and variance v, and A, B, and q are parameters estimatedfrom catch and effort data.
31

60

50

40

U;

c

E
..c

30

()

1ii

Without Stocking

U

20

10

o ':"-::t-T--t-----:t:-:-r---r--·--r--t-----:t-r---r---t----r---t:::::lj!=-oljI-.....---fil-~
~

~

~

~

M

M

~

M

M

1

U

U

~

0

~

~

U

~

~

2

Fishing Mortality / Natural Mortality

Figure 4
Equilibrium Ricker surplus production model with and without stocking. Curve without stocking based on biomass model B = 8 exp(0.7 - 0.0078); curve with stocking based on B = 8
exp(0.7 - 0078) + 25.

An experimental approach to stocking can be an efficientmeans of evaluating the effectiveness of stocking and identifying optimal stocking levels, but simulation of any design isa necessary first step before implementation. For example,
releasing juveniles into a fishery on alternating years and thencomparing catches in years with stocking to catches in years
without stocking may be considered a way to estimate theeffectiveness of stocking. This experimental design can be
simulated with the stocking surplus production model (Fig.
5). Suppose a population has a carrying-capacity biomass of
100 t and is fished with a fishing mortality of F= 1.0. Suppose juveniles are released in a quantity which contributes
20 t to the fishable biomass over a IO-year period on years
2,4, 6, 8, and 10, and no releases occur in years 1, 3, 5,
7, and 9. The stocking surplus production model estimatesthat equilibrium fishing with F= 1.0 results in a catch ofabout 49 t annually. The first stocking (year 2) increases thecatch to 62 t, and then the catch follows an oscillating sequence of lower catches during years without stocking andhigher catches during years with stocking. The oscillating
sequence has an increasing trend over time as the stock biomass grows due to stocking. At some point an equilibrium
would be reached and the sequence would oscillate between
the same two levels of catch. However, the use of this design
to estimate the effectiveness of stocking by comparing catches
between years with and without stocking would underestimate
the effectiveness of stocking at this level of fishing mortality,
since the catches do not return to their prestocking level
between years of stocking.

57
56
55

u; 54
C

E
..c
()

1ii

U

53
52
51
50
49
1

3

7

9

Years

Figure 5
Simulation of yield with F = 1.0 when stocking occurs on even numbered years. Parameters of the Ricker surplus production model withstocking are: A=1.2, B=O.OO7, a(H,)b=2Ot.

32

Citations_

Beddington, J.R., and J.G. Cooke1983 The potential yield of fish stocks.
47 p.

FAa Fish. Tech. Pap. 242,

Beverton, R.J.H., and S.J. Holt
1957 On the dynamics of exploited fish populations. Fish. Invest.
Ser. II Mar. Fish. G.B. Minist. Agric. Fish. Food 19, 533 p.

Botsford, L.W., and R.C. Hobbs
1984 Optimal fishery policy with artificial enhancement through stocking: California's white sturgeon as an example. Ecol. Model. 23:
293-312.

Isibasi, K.
1984 A statistical assessment on the effect of liberation of larvae inthe sea-farming-I. On the effect of liberation in the case of Kuruma
prawn (Penaeusjaponicus). Bull. Tokai Reg. Fish. Res. Lab. 113:
141-155.

Ludwig, D., and R. Hilborn
1983 Adaptive probing strategies for age-structured fish stocks. Can.
J. Fish. Aquat. Sci. 40:559-569.

Ludwig, D., and C.J. Walters
1985 Are age-structured models appropriate for catch-effort data?
Can. J. Fish. Aquat. Sci. 42:1066-1072.

Oshima, Y.
1984 Status of fish fanning and related technological development in
the cultivation of aquatic resources in Japan. In Liao, I.C., and R.
Hirano (eds.), Proceedings of ROC-JAPAN Symposium on Mariculture, p. 1-11. TML Conference Proceedings 1, Tungkang Mar.
Lab., Tungkang, Pingtung, Taiwan, R.O.C.

Peterman, R.M., and R.D. Routledge
1983 Experimental management of Oregon coho salmon (Oncorhynchus kisutch): Designing for yield of information. Can. J. Fish.
Aquat. Sci. 40: 1212-1223.

Ralston S.
1981 A study of the Hawaiian deepsea handline fishery with specialreference to the population dynamics of opakapaka, Pristipomoides
filamentosus. Ph.D. Diss., Univ. Wash., Seattle, 204 p.

Uchiyama, J.H., R.K. Burch, and S.A. Kraut1986 Growth of dolphins, Coryphaena hippurus and C. equiselis, in
Hawaiian waters as determined by daily increments on otoliths.
Fish. Bull., U.S. 84:186-191.

Ulltang,0.
1984 The management of cod stocks with special reference to growth
and recruitment overfishing and the question whether artificial propagation can help to solve management problems. In Dahl, E., et al.
(eds.), The propagation of cod Gadus morhua L., p. 795-817.
FI~evigen, rapp. 1.

Watanabe, S.
1985 Restocking effects on the two competing species system, including a nonlinear regulated species population. J. Tokyo Univ.
Fish. 72(2):57-63.

Watanabe, S., R. Matsunaga, and H. Fushimi
1982 Age-structured matrix model including catch and restocking.
J. Tokyo Univ. Fish. 68(1-2):15-23.

Yatsuyanagi, K.
1982 Productive effect in stocking of prawn seedling in water adjacent to Yamaguchi Pref. and Suho-Nada. Bull. Yamaguchi Prefect.
Naikai Fish. Exp. Stn. 10, 52 p. [in Jpn.].

33

Some Aspects of
Offshore Spat Collectionof Japanese Scallop

Scallop mariculture in Japan is a new and rapidly evolving
mariculture industry, presently very important in the northern part of Japan (Ito 1988, 1989b). Its development is attributed to the success of mass production of scallop seeds.
The seeds are produced from natural spat collection and intermediate culture in the sea. Although seed production first
took place in embayment areas, it is now practiced in shallow
waters of both embayment areas and the open sea. Off open
coasts, spat collection is frequently unsuccessful; however,spat collected offshore have become indispensable to theJapanese scallop culture industry in recent years. Therefore,
there is an urgent need to establish efficient methods for offshore spat collection. Some research has been done on thissubject and has provided clues to the establishment of suchmethods.
In this report, the author will review the biology of Japanese scallop and trends in scallop production and offshore
spat collection in Japan, and present results of recent offshore spat collection in Nemuro Straits, eastern Hokkaido.

HIROSHI ITO
Hokkaido Regional Fisheries Research Laboratory
Fisheries Agency of Japan
116 Katsurakoi, Kushiro City
Hokkaido, 085 Japan

ABSTRACTThe recent information on offshore spat collection of Japanesescallop, Patinopecten (Mizuhopecten) yessoensis JAY, is briefly
outlined. Scallop mariculture in Japan has developed rapidly
due to technical advances in the methods for spat collection andintermediate culture made in the mid-1960s. The spat collected
offshore is indispensable to Japanese scallop mariculture thathas evolved since the mid-1970s. Nevertheless, offshore spatcollection is frequently unsuccessful because of the intricate fluctuations in open sea conditions. Therefore, some research has
been performt:d in recent years on larval monitoring. The results
to date have shown that the scallop veliger larvae are distributed at comparatively higher densities in particular waters(temperature 7-SoC, salinity 32.0-32.5) along the coasts.

Biology of Japanese scallop_

Japanese scallop (giant yezo scallop), Patinopecten (Mizuhopecten) yessoensis JAY, "Hotate-gai" in Japanese, isclassified in the phylum Mollusca, class Bivalvia (Lamellibranchia or Pelecypoda), order Pteriomorphia, and family
Pectinidae. This scallop is a cold-water species distributedin the subfrigid coastal areas of the north Pacific Ocean, thesouth Okhotsk Sea and the Japan Sea, along the coasts of
the Kuril Islands, Sakhalin, Hokkaido, northern Honshu,
Sikhota Alin, and northern Korea. The southern limit of
the natural distribution in Japan is Toyama Bay on theJapan Sea coast and Tokyo Bay on the Pacific Ocean coast(Fig. 1).
The life cycle is as follows (Fig. 2): Demersal eggs fertilized in the sea after spawning. Fertilized eggs begin
cleavage and reach the trochophore state at 4 days. The earlyveliger larva with a fully formed prodissoconch shell, called
the D-shaped larva because of the straight hinge shell, isreached 5-7 days after fertilization. By 30-35 days, theumbones of the late veliger larva are fully grown andoverhang the straight hinge. The pediveliger attaches to thesubstratum with byssal threads 40 days after fertilization. Immediately after attaching, rapid changes in shell morphologyof the dissoconch (spat shell) and growth of internal organs
take place, leading to the adult scallop form (Yamamoto
1964, Maru 1972).
After the attached spat have grown to about 1 em shelllength, they start to be released from the substratum and thespat inhabit the sea bottom. This scallop is gonochoristic insexuality (Yamamoto 1943). Rarely, hermaphroditic individuals are found (Yamamoto 1964, Maru 1978b). Juveniles
are lacking in a well-developed gonad and differentiate sexually at about 15 months. Adults are more than 2 years old
35

14
~cS:P

~

JAPAN
SEA

145 E

'\OKHOTSK
SEA

Figure 1
Main scallop mariculture areas in Japan and natural distribution in the northern sea.

(Wakui and Obara 1967; Maru 1976, 1978a; Osanai et al.
1980; Kawamata et al. 1981). The gonads grow from autumn
to winter and become mature in spring. The eggs and sperm
are released after maturation in the spring.

Scallop production in Japanmesh size and "netlon net" in the larger. The bag filler isusually netlon net and waste fishing nets. The spat collectedby these collector bags hung from longlines are then caged
for seed production during a period of several months. This
cage culture for seed production is called "intermediate
culture." The intermediate culture seeds are used for hanging culture in exclusively designated sea areas and for sowing culture on prepared sea bottoms.
Scallop production in Japan remained at a low level of
5,000-20,000 metric tons for a quarter of a century, until
1970. After this, the hanging culture production increased,
mainly in embayment areas such as Mutsu Bay in Aomori
Prefecture, and Funka Bay and Saroma Lake in Hokkaido(Fig. 3). After 1975, the sowing culture production increased
rapidly, mainly in the coastal regions of Soya and Abashiri
in north Hokkaido, facing the Okhotsk Sea. In 1982, the production of hanging culture amounted to 77 ,000 tons, and the
production from sowing culture and fishing on wild stocks_

Scallop mariculture developed rapidly due to technicaladvances in the successful methods of natural spat collection and intermediate culture in embayments in the mid1960s. Scallop spat collection in Japan was first attemptedin Saroma Lake in 1934 (Kinoshita 1935). After many experiments, a successful scallop spat collector was invented
in 1964, primarily by Toyosaku Kudo, a fisherman in Mutsu
Bay, Aomori Prefecture (Yamamoto et al. 1971, Tsubata
1982). The scallop collector is composed of a mesh bag fIlledwith the substratum. The bag is made of a small or lltrge
synthetic fiber mesh, call "Japanese onion bag" in the small36

~
lot:::::

Ef. 55Un! e

J

S~.,m head 3-5 ~}GOnad i nde>tall 50-GOp~rt(~~1.ee~S:lggegg)

1 flO (70-100 /J)
Ii

iprecursor to ,moni toring thplanktonic
larva

Perti I inti on

Fertilized egg

I .

Developing embryo

Polar lobe stage

LarvalFirst cleavage

moni toring

Second cleavage
Third cleavage
Fourth cleavage

Age

Blastulao y'Gastrula

Prod i ssoconch stage

D_shaped larva< 150 /J" days
Trochophore larva
after ferti I iz.ation

I

5-7 days

Early vel iger larvaj150-190

Linbo-stage larva

190-240I.

30-35 days
"0 days

Late veltger larva(Pediveliger)

70-80 days

Attached spa t'1-5 months

Bottom Inhabiting spat

I
I

Early umbo-stage larva

I

plank10nanalysis

Earl Y full-grown larva\ Full-grown larva

250-280/1<. ..

Spatfallprediction

SPa1
}~ n

lcm<

I

Juver:i 1

Early grawn stage

La~te growing stage
De~enerating stage
Un~ifferentiated stage

Age

Intermediate
eul tureI

Dissoconch
stage

Differentiated stage(Sex different iated stage)~!2

Re'sting stage
EaJrlY growing stage

1

Late growing

Early growing stage

I

slage

Late growing stageI

Adul tI .

Maturing stage

Maturing stage~l
B r.eed i ng stage -----...,

01.
B r.ed ng lage

Spent stage

Spent stage

I
I

I

5

Hanging cuI ture0'

Sowing cuI ture

I.
I

Age

Resting stage

Resting stage

2 y'

Early growing stage

Early growing stage.nd

La te growi ng 5 tage

La te growing stage

older

Maturing stage

Maturing stage

1

I

1

1

U

~.

Life rycle of scallop

CuI ture method

Figure 2
Life cycle of the scallop PaJinopecten (Mimhopecten) yessoensis (Jay), with notes on culture methods. (Modified
from Yamamoto 1964; Maru 1972, 1976, 1978a,b; Kawamata et al. 1981.)

reached a little short of 100,000 tons, for a total productionof 176,000 tons.
The scallop takes first place, by value, in molluscan shellfish production in Japan, with a three-fold increase in production and a four-fold increase in value over the last 10
years. The value in 1982 amounted to 42 thousand million
yen. At present, sowing culture and wild production accountfor 56% of the total, and sowing culture keeps the scallop
industry prosperous. The rapid development of sowing
culture is attributed to the mass production of scallop seeds.
The number of seeds sown around Hokkaido amounted to1,500 million shells in 1982, a three-fold increase in the last

10 years (Fig. 4). Most of the seeds are sown in the coastal
retions of northern and eastern Hokkaido in this order:
Abashiri (990 million shells, 66 %), Nemuro (200 million
shells, 13%), and Soya (180 million shells, 12%). The seeds
for sowing culture are produced in the Rumoi, Soya, andNemuro regions, and depend mainly on offshore spat collection. These seeds, collected offshore, are mainly used forsowing culture. Therefore, offshore spat collection is equallyindispensable as collection in embayments for sowing culture.

37

80

HANGING CULTURETOHOKU

-

50

RuMO'
&
OTHERS
LAKE OF

II

~

:3o

1

IBURI HOKKAIOOI

BAY-.---,.---.,,---,-,--.-J,

ABASHIRI

10

'"o

~

M

Q

:

:>
oz

FUN<A

-------r-100°o:~ ',~~.~.~'.I ::~~
:1 'NSOE'M~AUR'O' ~_~--,-,
~-

x

15

5

o L,-..............-+.,...~;......,.....,...."'T"" .............-I
a:
w

llJ

WILD AND
SOWING CULTURE

2~Z
fHQI(KA1OO

10 O'--r-.--,.-,.-,-j------;r--.--r---,-----,-,---r--.

Ee
z

TOTAL

ow

z
o
i=
u
=>
o

w

(f)

5

~
a:
<I:

oa:

INDEPENDENT

w

c...

>1965

1975

1970

YEA

1980

1965

R

1975

YEA

Figure 3

1980

R

Figure 4

Recent trends in Japanese scallop production.

Offshore spat collection

1970

Recent trends in yearly seed input for scallop sowing around Hokkaido.

_

are the import-ant factors related to spawning, and are used
as a precursor to monitor the planktonic larvae. The gonadindex increases rapidly, reaches a maximum value in spring
before breeding, and then rapidly decreases to a minimumin summer after breeding. Changes in the index are monitored and the breeding time is estimated. Increases in watertemperature progress in the following order: Japan Sea coast,
Okhotsk Sea coast, and the Nemuro Straits coast (Fig. 8).
Likewise, scallop breeding along the open coasts around
Hokkaido generally begins first on the Japan Sea coast,
second on the Okhotsk Sea coast, and third in the Nemuro
Straits (Fig. 9). Local differences in breeding times are well
explained by differences in water temperatures. Coastal
surfacewater temperatures during the breeding period range
from 8 to 12°C; however, bottom temperatures are also
partially involved. The coastal surfacewater temperature is
2-3°C higher than the bottom temperature. Thus, the scallops
probably breed in 5-l0°C temperatures, but accurate measurements have not yet been obtained.

Offshore spat collection off open coasts has been done commercially since the mid-1970s (Maru and Nakagawa 1979,
Shiogaki et al. 1980). The spat collected offshore have accounted for half the seed supply for sowing culture since 1980
(Fig. 5). The offshore areas for spat collection operations
are distributed along the coasts of the northern Japan Sea,
the Okhotsk Sea, Nemuro Straits off Hokkaido, an Tsugaru
Straits and the Pacific Ocean off Aomori Prefecture. Mostof the offshore spat are collected around Hokkaido.
Environmental conditions of the open coast during spat collection fluctuate intricately because of seasonal changes in
the water masses from spring to summer (Fig. 6,7). The
Tsushima and Soya warm currents influence the waters
around Hokkaido to raise the temperature at this time
(Komaki 1975, Fujii and Sato 1977). Spat collection occurs
in the coastal areas directly influenced by coastal waters, andindirectly influenced by oceanic waters.
The breeding season of scallops along the open coasts
around Hokkaido extends from April to July. The scallop
is induced to spawn by factors controlled by the animal itself
and by environmental conditions. The gonad index (gonad
weight x lOO/soft body weight) and the water temperature
38

'3
<{

15

::J

0

:;
15

co

~

$2
x
0
W
f-

10

w

::,L

a:

NEMUROISHIKARISHIRIBESHI
SOYA

«
~
a:
w

m

5

~

HOKKAIDO

=>
Z
0

w
w

(f)

0
1965

1975

1970

Y

E

A

1980

Figure 5R

Recent trends in number of scallop seed marketed.

The scallop larvae are monitored with plankton analysis
for spatfall prediction. In embayments, the densities of thelarvae usually range from 100 to 10,000 individuals/m3
seawater (Maru 1985). Nevertheless, the offshore larvae arevery few and their densities fall to lower levels, 10% to 1%of those in embayments (Fig. 10). As a result, industrial
methods for offshore spat collection are at present notestablished, and collection is frequently unsuccessful. Moreover, data realted to this are scarce. Therefore, research has
been carried out in offshore areas for spat collecting, andfollowing are the results of our research in Nemuro Straits.

SUMMER
19··.

Research in Nemuro Straits_

Industrial spat collection has been attempted since 1977 in
Nemuro Straits (Fig. 11), east Hokkaido, near the southern
Kuriles, although it was unsuccessful during the period
1977-81. In 1982, a research project for this region was
begun by this author and co-workers of a special teamorganized to concentrate systematically on creative conceptsof scallop mariculture (Ito 1989a). The research area extended along 350 kIn of coastline from the Shiretoko Peninsula facing the Okhotsk Sea to the Nemuro Peninsula facing
the Pacific Ocean. Water depths investigated range from a
few to 1000 meters, since the northern region becomes rapidly deeper than the southern. The vertical search range extended to depths of 70 m and to plankton living at less than
20-m depths. The biological and environmental research took
place aboard four vessels at half-week or one-week intervals for 4 months, from April to July.

WINTER

Figure 6
Main water currents around Hokkaido, summer and winter.

39) SPRING:1:111111

JAPAN:SEA IMASHIKE
COASTIITOMAMAE,HABORO

u:
I
I

I

~ 1

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o

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COAST II

lko

1 [RAUSUI

NEMUROINEMURO
STR. I
COAST:

JAN.

40

Figure 7
Seasonal water masses around Hokkaido. A, Tsushima warm current;
B, Tsugaru warm current; C, Soya warm current; D, northward current of the Kuroshio; E, coastal branch off the Oyashio (Kuril cold current); F, offshore branch off the Oyashio (Kuril cold current); G, east
SakbaIin cold current; H, Liman cold current; I, west Sakhalin coastal
water; J, cold water west off Tsugaru Straits; K, cold water west off
Musashi-tai; L, inter-cool water; M, mixed water area of circulating
current; N, floating ice area; 0, coastal water area. (After Komaki 1975,
Fujii and Sato 1977.)

Figure 8
Surface temperature changes of coastaI waters relative to locality around
Hokkaido, 1982.

A
JAPAN

• • ••

•

•

OOMU

COAST

•
~~

. -..
•

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Figure 10

NEMURO

Changes in numbers of scallop veligers and attached spats on the coastsof Okhotsk Sea and Nemuro Straits off Hokkaido, 1982.

I STRAITS
COAST

40
30

NOTSUKEb ~I ~~ :

.~

20

rr

10

J

~oo'ib

0

MAR.

APR.

P

MAY

JUN.

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JUL.

Figure 9
Changes in gonad index (gonad weight x 100/soft body weight) of adultscallop relative to locality around Hokkaido, 1982.
41

145' E

5I

oKHOT SK

o

I

10

OCEAN

Figure 11
Location of Nemuro Straits.

In Nemuro Straits, the spawning period varied with thelocation of the scallop habitat. For 1982 it was estimated tobe (Fig. 12) early-June to early-July at Rausu (northern
region), mid-June at Shibetsu (middle region), and late-May
at Bekkai (southern region). In short, the scallop spawned
earlier in souther than in northern areas. This is well explained by the time lag in temperature increase. Bottom
temperatures at spawning are similar at different localities,
with a range of 5-7°C. Further, the scallop is induced tospawn by an abrupt rise in temperature. Spawning wasobserved in 1983 after a slight temperature increase, as little as 1°C, at the bottom, as a result of rough weather (Figs.
13, 14).

The distribution of planktonic larvae shows fast-moving
kaleidoscopic changes, with time (Figs. 15, 16). Environmental conditions of the open coast also fluctuate intricately
and are not easily forecast. However, it appears possible todraw conclusions from the phenomena observed. The larval distribution is not regulated simply by temperature andsalinity, but seems to have some relation to water masses
in the coastal areas. The waters with high densities of larvae have salinities of 32.0-32.5 and temperatures of 7-8°C(Fig. 17). Consequently, we have concluded that the larvae
are distributed with comparatively high densities in particularwater masses of the coastal waters.

42

SHIBETSU

RAUSU
~
><
L.I.J

11!

c:I

:z:: 40
c:I
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~

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3 4

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567

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Figure 12
Changes in gonad index and water temperature in Nemuro Straits, 1982.

Citations

The results mentioned above are preliminary, and moredetailed research will be undertaken. However, industrial
spat collection in the Nemuro Straits has been successful since
1982, thanks in part to the results of this research project.
At present, offshore spat collection is indispensable toscallop production in Japan. Some research has been performed to establish efficient methods for offshore scallop
spat collection, and some information has been obtained onscallop spawning habits, larval distribution, and environmental conditions. In some regions, industrial spat collection ispresently successful after the results of our project in the
Nemuro Straits; however, successful methods for spatcollecting in other regions need to be established.

Acknowledgments_

Fujii, K., and Y. Sato
1977 Characteristics of primary production in the cold region waters.
Rep. Fish. Res. Invest. Jpn. Gov. 20:25-46 [in Jpn.l.
Ito, H.
1988 Sowing culture of scallop in Japan. In Sparks, A.K. (ed.), New
and innovative advances in biology/engineering with potential for use
in aquaculture; Proceedings of fourteenth U.S.-Japan meeting on
aquaculture, p. 63-69. NOAA Tech. Rep. 70, U.S. Nat!. Oceanic
Atmos. Adm., Natl. Mar. Fish. Serv.
1989a Concept in mariculture of Japanese scallop. Scallop (Kushiro)
2:89-97 [in Jpn.].
1989b Scallop mariculture and fisheries in Japan. Scallops: Biology,
ecology and aquaculture. Elsevier Sci. Pub!., Amsterdam.
Kawamata, K., Y. Tamaoki, and A. Fuji
1981 Gonad development of the cultured scallops in Funka Bay. J.
Hokkaido Fish. Exp. Stn. (Hokusuisi Geppo) 38: 132-145 [in Jpn.].
Kinoshita, T.
1935 "Hotate-gai saibyo shiken" [An experiment on natural spat collection of Japanese scallop]. Rep. Hokkaido Fish. Exp. Stn.
(Hokusuisi Junpo) 273:1-8 [in Jpn.].
Komaki, S.
1975 "Senkai gyojo kaihatsu to gaikai joken" [Development of thecoastal fishing ground and conditions of offshore water]. Suirikogaku ser. 75-B-5 [in Jpn.].
Maru, K.
1972 Morphological observations on th veliger larvae of a scallop,
Patinopecten yessoensis (JAY). Sci. Rep. Hokkaido Fish. Exp. Stn.
14:55-62 [in Jpn.].
1976 Studies on the reproduction of a scallop, Patinopecten yessoensis (JAY) - I. Reproductive cycle of the cultured scallop. Sci. Rep.
Hokkaido Fish. Exp. Stn. 18:9-26 [in Jpn., Eng!. abstr.]_

The author wishes to express sincere thanks to the following coworkers of a special team: Messrs. T. Fujimoto,T. Sasaki, H. Moriya, T. Ikeda, T. Abe, and Y. Nakata for
their "Jingi" friendship.

43

~

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Figure 13
Changes in gonad index relative to sea conditions off Shibetsu, 1983.

44

JUN.

31.8
32.0

31.4

15

15

A

,

,:f ~
0

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32.0
32.2

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FIGURE NO, 1

3

UEBETSU DATE: 19 APRIL

29 A"SYMBOLIZED ,,INDICATION..
'Of,
UN~A .. BOTTOM'
BETS"TEMPERATURE"

•

IMUI

KOTAJ\IUKA

-

~ 'I"

I

\
_ 4 . 5 C\'.~

'0 <4,5 C 'CHURUI@B'

4
4 MAY

0'
0'

®

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SITEOfSHIBETSU
ADULT
SCAllOPS®

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CHAN I

5
9M

6
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7

8

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12

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Figure 14
Horizontal changes in bottom temperatures of adult scallop habitat off Shibetsu, 1983.

45

,100

~50
JO

Figure 15
Weekly changes in density of scallop larvae in Nemuro Straits, 1982.

46

24

22 JUNE '82.

• •

26

•••••
•

•

1 JULY

4

25

5

2

6

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Figure 16
Daily changes in density of scallop larvae off Shibetsu, 1982.

19783 Studies on the reproduction of a scallop, Patirwpecten yessoensis(JAY) - 2. Gonad development in I-year-old scallops. Sci. Rep.
Hokkaido Fish. Exp. Stn. 20: 13-26 [in Jpn., EngJ. abstr.].
1978b Studies on the reproduction of a scallop, Patirwpecten yessoensis(JAY) - 3. Observations on hermaphroditic gonads. Sci. Rep. Hokkaido Fish. Exp. Stn. 20:27-33 [in Jpn., EngJ. abstr.].
1985 Ecological studies on the seed production of scallop, Patirwpecten
yessoensis (Jay). Sci. Rep. Hokkaido Fish. Exp. Stn. 27, 53 p. [inJpn., EngJ. abstr.].
Maw, K., and Y. Nakagawa
1979 "Hotate-gai gaikai saibyo shiken" [Researches for offshore spatcollection of Japanese scallop]. Annu. Rep. for 1978, Abashiri Fish.
Exp. Stn .• Hokkaido. p. 139-149 [in Jpn.].
Osanai, K., S. Hirai, and M. Odashima
1980 Sexual differentiation in the juveniles of the scallop. Patirwpecten
yessoensis. Bull. Mar. BioI. Stn. Asamushi 16(4):21-230.
Shiogaki, M., S. Aoyama, E. Kitano, H. Sugawa, and Y. Uemura
1980 "Gaikai hotate-gai saibyo shiken" [Experiments on offshore spatcollection of the Japanese scallop]. Annu. Rep. 9, AquacuJ. Cent..
Aomori Prefec .• p. 78-81 [in Jpn.].

Tsubata, F.
1982 "Mutsu-wan hotate-gai gyogyo kenkyu-shi" [A history of thefisheries researches of the Japanese scallop in Mutsu Bay]. Aomori
Prefecture. 120 p. [in Jpn.].
Wakui, T., and A. Obara
1967 On the seasonal change of the gonads of scallop, Patinopecten
yessoensis (JAY), in Lake Saroma. Hokkaido. Bull. Hokkaido Reg.
Fish. Res. Lab. 32:15-22 [in Jpn., Engl. abstr.].
Yamamoto, G.
1943 Gemetogenesis and the breeding season of the Japanese common scallop, Pecten (Patinopecten) yessoensis JAY. Bull. Jpn. Soc.
Sci. Fish. 12:21-26 [in Jpn., Engl. synop.].
1964 Scallop culture in Mutsu Bay. Suisan Zoyoshoku Sosho 6, 77
p. [in Jpn.].
Yamamoto, G., S. Ito, N. Nishikawa, and A. Fuji
1971 "Hotate-gai yoshoku no shinpo" [Development of the Japanesescallop culture]. Complete mariculture in shallow waters. Koseisha
Koseikaku (Tokyo). p. 187-263 [in Jpn.].

47

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Enhancement of
Molluscan Shellfish
in Washington State

The state of Washington has about 2,700 miles of marine
shoreline and major stocks of molluscan shellfish yielding
over 30 million pounds annually. Between 1950 and 1985,
the State's population increased from 2.3 to 4.3 million people. At the same time, the demand for shellfish increased
by a factor of about four due to increasing recreational andcommercial use. At present, demand far exceeds the supply. To fill the need, effort has been directed to increasing
stocks of shellfish, and this report describes enhancement
methods being employed by the Washington State Department of Fisheries for three different clam fisheries.
Geoducks are large (up to 10 pounds) clams found primarily subtidally, but also low on intertidal beaches. This clam
has long been popular on intertidal sport beaches, and isharvested commercially (up to 5 million pounds per year)
by divers. The primary factor limiting geoduck harvest is
its very slow natural recruitment rate, although the clams
grow to commercial size rapidly. This creates an opportunity for enhancement through artificial seeding of the clam
beds, and we are developing a hatchery system initially aimed
at doubling current harvest levels.
Razor clams are a very popular sport clam taken along 60
miles of intertidal ocean beach. Harvest is by hand-digging
at low tide. Digging pressure has more than doubled during
the past 35 years, while clam setting has markedly decreasedon about one-third of clam beds. One method used to increase
the abundance of clams is to transplant naturally produced
razor clam seed from subtidal areas of high abundance tothe low-abundance areas on intertidal beaches.
Hardshell clams are highly prized by sport and commercial users. Clam abundance remains generally good, but
demand far outdistances the supply. One of the major limitations on stocks is lack of suitable habitat for larval settlement and growth. These clams require a sand-mudgravelmix, and will not grow on mud or sand flats. The Washington
Department of Fisheries and the industry are developing techniques for creating new clam beaches by spreading a layerof gravel 4-8 inches thick on non-clam producing beaches.
High success occurs when beaches are carefully selected.

RONALD E. WESTLEyl
NEIL A. RICKARD
Shellfish Division
Washington Department of Fisheries
Olympia, Washington 98504

C. LYNN GOODWINALBERT J. SCHOLZ
Pt. Whitney Shellfish lAboratory
Washington Department of Fisheries
Brinnon, Washington 98320

ABSTRACTThe Washington Department of Fisheries has undertaken augmentation of natural stocks of three clam species. We are applying new enhancement methods in an optimal environment formolluscan shellfISh to meet increasing seafood demands. The
approach taken in each case has been to carefully evaluate bothbiological and economic aspects of enhancement and to selectthe method that best fits the particular circumstances. The work
carried out demonstrates that a variety of techniques are available (hatchery seeding, transplantation of natural seed, andhabitat improvement). However, it also clearly demonstrates
that the more comprehensive the initial assessments can be, thegreater the chances of success.

Geoducks_

During the summer of 1967, the Washington Department of
Fisheries began surveying the shallow subtidal region of
Puget Sound to determine the extent of the geoduck resource.
These surveys, conducted by SCUBA divers, have continued
to the present time. From the beginning of the surveys, large
numbers of geoducks Panope abrupta, formerly generosa,
were found, justifying harvest of this unexploited resource.
In 1969, the Washington State Legislature provided for acommercial geoduck fishery beginning in 1970. Current law
limits the fishery to divers using hand-held gear and to waters
greater than 18 feet deep and further than 200 yards fromthe mean high-tide line.

'Deceased July 1989.

49

Distribution and abundance

1980
1981
1982
1983
1984
1985

Geoduck clams are found in North America from Alaska to
California, with the population center in Puget Sound andBritish Columbia. Large populations of geoducks have also
recently been reported in Japan. Survey results for geoducks
in Puget Sound are as follows:
Geoducks(million pounds)
Acres
Observed geoduck beds
Major and commercial beds
Commercial beds
Annual harvest fromcommercial beds

33,79919,545
8,378

280
165

200-300

5Enhancement
A geoduck hatchery and juvenile grow-out facility is operating at the Point Whitney Shellfish Laboratory, Washington Department of Fisheries. The hatchery and its operation
are financed through the Washington Department of Natural
Resources from sales of geoduck harvest rights to commercial fishermen. The primary goal of the hatchery system isto restock harvested subtidal geoduck beds with cultured
seed. Artificial seeding, if successful, could greatly reduce
the time-interval between crops from individual beds. The
first large-scale plantings were in 1985, when 250,000 seed
were planted, and in 1986 when 1.6 million seed wereplanted. The long-range goal is to increase production in thehatchery until 30 million seed/year are available for planting to support an additional 5-million-pound harvest eachyear.

Life history
Geoducks are the largest-known burrowing clam in theworld. In Puget Sound adult clams weigh an average 1.9
pounds, and may reach 10 pounds. A geoduck begins lifein the spring, when spawning adults release millions ofgametes into the water. For 3-5 weeks, larval clams driftwith the currents and may be transported far from the parental
bed. They soon lose their ability to swim, settle to the bottom, and burrow into the substrate, usually down to 2-3 feet,as they grow. Burrowing ceases as clams reach adult size.
The major factor limiting geoduck production is the very
slow rate at which new clams are recruited into the population. Although the clams grow rapidly, it takes 15-60 years
for a harvest population to be replaced naturally.
Geoducks are commercially harvested from subtidal beds
by divers using hand-held water jets. The water jet used toharvest the clams is a short pipe ('" 18 inches long) with
5/8-inch diameter tip at the digging end, and a shut-off valve
on the other. Geoducks are harvested individually. The
animal is located by its "show" (neck extended out of thesubstrate), or by feeling for depressions in the substrate leftwhen the neck is withdrawn. The nozzle, placed next to theshow, liquifies the substrate immediately around the clam,allowing the geoduck to be pulled out.
An experienced diver harvesting a good bed can dig ageoduck in 15-30 seconds, and may harvest up to 2,000
pounds per day under ideal conditions. Following is a summary of geoduck harvests in Puget Sound, 1970-85:
Year

Pounds

1970
1971
1972
1973
1974
1975
1976
1977
1978
1979

82,236610,250
493,140
463,994
803,358
2,372,271
5,365,898
8,646,746
7,089,656
5,228,215

3,910,192
4,290,127
5,303,081
3,523,450
4,421,265
4,109,000

Hatchery Young clams (6-12 years old) are preferred forbrood stock because of better quality eggs. Spawners arebrought into the hatchery from December to July to coincide with the natural spawning season. Spawning is accomplished by stimulation with high-density algae. The larvae
are normally ready to metamorphose 20-21 days after
fertilization.
During the first 10 days, the larvae are fed a combinationof Chaetocerus calcitrans and Tahitian Isochrysis. After collection on a 120-ji screen, they are fed a mixture of 70%
Thalassiosira pseudonana, 20 % Tahitian Isochrysis, and
10% Dunaliella tertiolecta.
Field planting The commercially harvested beds being
replanted with hatchery seed are all subtidal, so the standard
method of intertidal clam reseeding furing a low tide cannot
be used. Two basic methods of subtidal seeding are: 1) Hand
planting by divers (good only for small experimental plots),or 2) surface planting from boats, allowing the seed to fallto the bottom where they attach and burrow.
We have developed a geoduck seeder mounted on the backof a 28-foot boat. The seed is placed in a cone-shaped tankwith seawater injected at the bottom. Eight siphons carry thesuspended seed in equal amounts, via plastic hoses, to theeight distribution nozzles, each 4 feet apart. Seeding is accomplished by running the boat over the area to be seeded
in long transects. Each pass covers a strip about 40 feet wide.
Aliquots of seed are dumped into a cone tank as the boatproceeds down the transect line. By varying the number ofaliquots per unit of time and the speed of the vessel, thedensity of seed reaching the bottom can be controlled. We
normally plant between 10 and 20 seed/m2 .
50

environment, they grow while subjected to tremendous
natural mortality. They also move, either voluntarily or involuntarily, toward the beach. Some of the survivors aredeposited on to the unstable high-energy intertidal beach as
5-15 mm juveniles. Within a year, the survivors are 2-2.5
inches in length and are recruited into the fishery the next
year as 4-4.5 inch clams.
During the past 35 years, intertidal razor clam stocks havesteadily declined due to intense harvest, inconsistent natural
reproduction and reduced setting, and recent disease mortalities. In 1979 the Washington State Legislature directedthat new efforts be undertaken to offset this decline, including
enhancement of clam stocks to increase the number of razor
clams available. One method bdng attempted is to seed intertidal areas of depressed natural clam abundance with large
numbers of juveniles obtained from subtidal areas.

The water currents and water depth affect lateral drift ofthe seed as it settles through the water column. The settling
speed of the seed is directly related to seed size. Clams 8mm in length settle through the water at a rate of 7 cm/
second.
Predation during seeding has been a major concern. However, significant loss of the seed as it passes through the watercolumn has not occurred, even though various types of potential predators have been present during seeding. After landing on the bottom, the seed must burrow rapidly to avoid
surface-feeding benthic predators such as flounders, soles,
crabs, snails, and starfish. Burial time is inversely related
to seed size. Seed 1-2 mm in size will become burried in
4-5 minutes; lO-mm seed requires up to 30 minutes forburial. During the first 2 years oflife after planting, the seedis susceptible to such predators as starfish, crabs, andmoonsnails , that can dig into the substrate and attach thejuvenile clams. After 2 years, the clams are normally buried
deeply enough in the substrate to be free of predation.
Seed survival after 2 years in small experimental plots hasvaried from 0 to 40 %, with most experiments averaging
between 2 and 5 %. Predation is thought to be the primaryreason for losses, although predator exclosures, such as
screens and cages, have not increased survival. Seed size,
substrate type, particle size, and compaction appear to beimportant to survival. Seed of 3-8 mm shell length at planting have never shown survival greater than 5 %. Of seed
averaging 13.5 mm shell length, 40% survived in one experiment in a compact muddy area; but only 1.35% survived
in a soft sandy area.
Seed growth after planting varies according to the area
planted, but can be very rapid. Planted seed can reach 2
pounds in 4 to 5 years.

Razor clams

Enhancement
The large populations of juvenile razor clams on recreationally inaccessible subtidal beds provide a potential source of
seed for replanting intertidal sport beaches. Initial work involved developing gear and techniques to harvest the seed
and transfer it to intertidal beaches, and then surveying thenearshore area for major beds of seed clams.
To harvest the seed clams, a small hydraulic-airlift harvester was developed. The clams are separated from the sandsubstrate by water jets and then lifted to the surface by anairlift. Harvest is from a 34-foot boat in shallow waters 10-40
feet deep during calm seas. The seed harvested is 5-15 mm
in length.
In late July 1985, 21 tows were made in 6 days of harvesting. A total of about 9000 juvenile razor clams were harvested. Six tows on 6 August yielded over 6.3 million
juveniles while the next day, 7 August, eight tows produced
over 15.5 million juveniles. These high recoveries demonstrated the potential feasibility of the harvest method.
Subsequently, a special survey was undertaken to determine the extent of this available resource. Juvenile clamdensities were found to be highest in the vicinity of thenorthern beaches. Between 6 August and 10 October, 84 tows
yielded over 127 million juvenile razor clams. Of these, 93
million were transplanted to the beaches south of Grays
Harbor, Twin Harbors, and Long Beach. Based on thesesurveys, it was conservatively estimated that there were approximately 28 billion juvenile clams present in the 5-km2
subtidal area near Iron Springs where maximum densities
exceeded 13,000/m2 • Later harvests in early October produced over 19 million juvenile clams per day which averaged 5 mm (range 1-15 mm).
At the end of each day's harvest, the seed clams are taken
ashore and manually planted on the beach at low tide. Several
experimental planting methods were tried. The most successful was to place the seed in large buckets and pour the contents on the sand ahead of an advancing wave. Although theseed clams dig into the sand within minutes, planting is best
done at night on an incoming tide to minimize dessication_

The Pacific razor clam Siliqua patula inhabits Washington's
open, wave-swept coastal beaches from the mouth of theColumbia River north to the Quinault River, and on small
isolated beaches north to Cape Flattery. It supports an intensive recreational fishery on the Washington coast. Historical annual harvest effort has been about 700,000 digger
trips, yielding approximately 1.3 million pounds of clams.

Life history
The Pacific razor clam is found in North America from central California to Alaska, with the largest population available for recreational harvest occurring in Washington. Localrazor clams may live 5-8 years; however, most are harvested
by age-3. Reproductive maturity occurs by age-2, and spawning usually takes place in late spring. Larval survival anddistribution are dependent on both favorable ocean currents
and weather conditions.
Settlement of juvenile clams into the substrate occurs invery large numbers subtidally. In this comparatively stable
51

and predation. Even with this manual method, large plantings can be accomplished in a short time-period.
The harvest method is clearly successful and cost effective. The unknowns are:

4 Avoidance of areas with major abundances of known clam
predators.
Cost of graveling is variable but is estimated to be about$12,000 per acre. When in production, each acre should havean annual yield of 15,000 pounds of clams.

1 What is the survival of the planted clams? Studies areunderway to assess survival. Early indications are that adequate survival occurred.
2 Will subtidal sets occur with sufficient regularity to makethis a useful technique? If seed is available at least once in
3 years, it will be viable. If seed is available only once in
10 years, it would be of limited value. In 1988, nearly 3.3
million juvenile clams were again harvested from the area
near Iron Springs. These clams were also transplanted to thebeaches south of Grays Harbor. Therefore, preliminary indications are that subtidal seed will be available at least once
every 3 years.

Hardshell clams_

Sport utilization of hardshell (manila and native littleneck)clams has increased from about 250,000 user trips in 1950
to over 1 million in 1985. Commercial production has morethan doubled. Total harvest currently is about 4.8 million
pounds per year. Since one major limitation to productionof these highly valued clams is lack of the needed sand-mudgravel substrate for settlement and survival of clam larvae,
there is a major focus on modifying new beach substrate toincrease production. Starting in the 1960s, the industry, andmore recently the Washington Department of Fisheries, haveembarked upon beach enhancement by spreading 1-8 inchesof gravel over previously unsuitable habitat to create newclam ground.
The gravel used is a mixture of rock measuring 1/4-inch
up to a maximum of 3 inches in diameter. Normally, gravelis hauled-in by barge, dumped at high tide, and then spreadmechanically at low tide. It normally takes a minimum of
3 years after placement before clam production begins.
Major factors in successful clam production include:
1 Selection of areas where good populations of free-swimming clam larvae are present.
2 Selection of areas where the gravel will stay effectively
in place for at least 20 years. Areas of excessive storm (wave)
exposure and of heavy silt deposition or major longshore current should be avoided.
3 Avoidance of areas with heavy organic loading in theexisting substrate. Placement of gravel in these conditions
usually results in production of hydrogen sulfide and will
foul the ground for 2-4 years. It is also wise to avoid areasof dense eelgrass or seaweed. At the very least, gravelingshould be done when stands of grass are at a seasonal minimun. Freshwater run-off can result in siltation of gravel plots
when combined with poor upland management.

52

The Role of
Aquaculture in
the Restorationand Enhancement of
Molluscan Fisheries inNorth America1

Decreases in shellfish stocks, whether resulting from overfishing, parasites, predators and disease, or unusual environmental perturbations, often prompt management agencies toencourage or implement stock enhancement programs. These
programs have as an ultimate goal either the rebuilding ofdepleted fishery stocks, or the augmentation of natural stocks
to support an artificially high maximum sustainable yield.
The shellfisheries of North America have not traditionallyrelied upon restoration or enhancement programs to augment
wildstock populations. Fishery practices, such as the translocation of seed from natural beds to grow-out areas or the
regular replanting of shellstock as cultch during periods whennatural set is occurring, have long been part of the oyster
industry (Beaven 1953, Tarver and Dugas 1973, Reisinger
1978, Dugas 1984). Similar activities, albeit on a more
limited scale, have been practiced with other bivalves including the softshell clam, hard clam, and scallop (Turner
1951, Dow 1953, Mackenzie 1979).
Recently, the success of large commercial-scale mollusk
aquaculture operations and the continued decline of wildstock
resources have prompted an evaluation of the use of intensive aquaculture in the restoration and/or enhancement ofwildstock fisheries. This paper will provide a survey of molluscan aquaculture technology applicable to restoration orenhancement programs, with particular attention to the use ofhatcheries as a fishery management tool and the role of genetics in molluscan fishery enhancement. To place the problem in perspective, we will first address two case histories
involving management practices influencing mollusk fisheries.

JOHN J. MANZIMarine Resources Research Institute
P. O. Box /2559
Charleston, South Carolina 294/2

ABSTRACTThe natural populations of most commercially important speciesof bivalve mollusks continue to decline in North America. As
these stocks decline and their commercial and recreational values
increase, aquaculture becomes an appreciably more attractive
alternative for the restoration and/or enhancement of molluscan
fisheries populations. The historical uses of aquaculture to initiate, and eventually supplement, the Pacific oyster fIShery in
the northwestern United States and British Columbia provide
a good model for the development of fisheries management
through the intercession of aquaculture. This paper reviews two
approaches to the incorporation of aquaculture in the management of restoration or enhancement of molluscan fIShery stocks:(1) Use of hatcheries as management tools, and (2) the role ofgenetics in mollusk fIShery enhancement. Both approaches havesignificant potential for mollusk fISheries, but both are prone
to an eventuality which can include long-term detrimental impacts on fIShery populations. The inevitable conclusion is that,provided we learn from previous mistakes of the salmonid
fISheries, both hatchery production and genetic manipulationof resource populations can provide significant relief to themolluscan fisheries of North America.

A case history: Oyster culturein the Pacific Northwest_

Aquaculture has played a significant role in the oyster industry of North America. Postset and seed of the Americanoyster, Crassostrea virginica, have been produced by hatchery and nursery systems for many years. This stock enhancement had been relatively small until recently when set,
produced by commercial culture, has made a significant
impact in certain parts of the United States. The oyster
industry of Long Island epitomizes this impact. At present,
one hatchery on Long Island provides nearly a third of thetotal oyster seed planted in western Long Island Sound.
Hatchery-produced set are reared in trays suspended fromrafts until they attain a size of 10-15 mm. The seed are thenbroadcast over prepared bottom for grow-out.
Although an appreciable dependence between hatchery/nursery-produced seed and the oyster fishery of Long Island
Sound has been demonstrated, development of the Pacificoyster, Crassostrea gigas, fishery and its continued existence depends on commercial aquaculture participation. For
many years, no wildstock fishery for the Pacific oyster existed on the west coast of North America. All oysters weregrown to market size from seed imported from Miyagi andKumamoto prefectures in Japan. In the 1960s, C. gigas began'Contribution no. 300 of the South Carolina Marine Resource Center.

53

appearing in signiticant natural spatfalls in Washington State(A.K. Sparks, Alaska Fish. Cent., Natl. Mar. Fish. Serv.,
NOAA, 7600 Sand Point Way N.E., Seattle, WA 981150070, pers. commun., Oct. 1986). These spat, along withthose produced through commercial hatcheries, have supplied a greater and greater proportion of the seed used in
the Pacific oyster grow-out industry (Chew 1979). The contribution of seed from hatchery intervention has become
significant. One hatchery in Washington State produced 18
billion spat in 1986 (J. Donaldson, Coast Oyster Co.,
Quilcene, WA, pers. commun., Oct. 1986) and will supply
seed to grow-out facilities from Quilcene Bay, Washington,to Humboldt Bay, California. The same hatchery has helped
develop and standardize methods of transporting late-stageor "eyed" oyster larvae for setting in other locales. This
technique of "remote setting" has expanded the industry considerably by providing a low-cost, on-site seed producing
capability to the growers of the Pacific Oyster.

A case history: Spawner transplantingof the hard clam

Table 1
Percentage of clams in spawning and spent stages of gametogenesis
in native and transplanted populations of hard clams, Mercenaria
mercenaria, in Great South Bay, New York (data from Kassner andMalouf 1982).
Native clams (%)

Spawner transplants (%)

Date

Spawning

Spent

Spawning

Spent

6/211786/25178
7/071787120178
8/10178

0
18
13
0
0

0
0
85
100
60

0
35
5
0
0

0
20
100
100
75

negligible. They indicate that typical annual transplants involve about 500 to 1,000 bushels (18-36 m3) of chowder
clams. Assuming there are about 250 clams/bu (7,000 clams/m3), a typical operation would transplant 250,000 clams,
one-half or 125,000 or which would be females. If it is also
assumed that an average gamete release of Great South Bay
female chowder clams is 106 eggs (Bricelj and Malouf1981), then one could expect a maximum of 7.5 X 1011
larvae introduced to the system by the spawner transplants.
Extrapolating from the data of McHugh (1981) who estimated
egg production from natural clam populations in the eastern
half of the Bay, we find that a total larval production for
the entire Bay may well exceed 11.0 X 10 15 per year. It
would appear that the spawner transplants would contribute,at best, no more than 0.005 % of the total annual larvae production in Great South Bay.
Although this analysis of spawner transplants in GreatSouth Bay is less than encouraging, the concept of introducing spawners to provide larvae for areas devoid of clams isreasonable. Spawner transplants do have the capacity ofproviding seed to limited areas where larvae would notnormally present.

_

Great South Bay on the southern shore of Long Island, New
York, is the largest producer of the hard clam, Mercenaria
mercenaria, in the world. This one fishery produces about$20 million annually (Kassner and Malouf 1982) from landings that average about 400,000 bushels a year. The importance of this fishery is demonstrated by the number ofmanagement practices applied by state and local regulatory
agencies. Among these are limitations on daily harvests,
fishing gear, and minimum marketable sizes, as well as
restoration programs involving the planting of seed clams
and/or the transplanting of ripe spawners into the Bay during spawning seasons (Bricelj and Malouf 1981, McHugh1981). The rationale behind the spawner transplants is basedon the belief that highly fecund spawners introduced to the
Bay from a more northern area would result in greater
recruitment. It was thought an increase in recruitment would
come about for two reasons: Spawners would add more larvae to the Bay milieu, and the spawning of the transplants
would be asynchronous-spawning later than the native
stock. The combined result of this introduction would thus
be not only an increase in the total quantity of larvae available to the year-class but also an increase in the length oftime that larvae would be in the Bay and exposed to favorable environmental conditions for settlement.
Recently, Kassner and Malouf (1982) performed a study
evaluating the benefits of spawner transplants in Great SouthBay. Their results, reported in Table 1, invalidate theassumption that the introduction of spawners serves to introduce larvae at a time when they would not otherwise beavailable from native stocks, at least during the year this study
was performed.
If spawner transplanting does not provide larvae to theGreat South Bay system when they would not otherwise bepresent, can it significantly supplement the natural set?
Kassner and Malouf (1982) suggest that the contribution is

Hatcheries as a management tool_

A paradigm of fishery management states that populationenhancement programs cannot consistently and predictably
benefit fishery populations that are regulated by densityindependent factors. If, however, (1) a fishery populationis regulated by density-dependent factors, (2) the environment is capable of sustaining introduced additions to thispopulation, and (3) it is technically possible to produce large
numbers of high quality seed on an economical basis, thenhatcheries can be used to effectively intercede in fisheries
restoration and management activities.
The success of finfish hatcheries in the augmentation of
salmonid populations has stimulated interest in hatchery production as a management tool in molluscan fisheries (Malouf1989). Augmentation of natural populations has a long history
in the mollusk fisheries. Traditionally, seed transplanting programs, particularly for oysters, have been part of most fish54

sterile adults. This was an important result for the fishery,because it has traditionally suffered during periods when the
resource was reproductively mature (ripe and spawning). An
oyster with ripe gonads was unattractive for the half-shelltrade, and subsequently the market and price were depressedin the spawning season. With the advent of triploid oysters
and their characteristic lack of gonadal tissue, an opportunity developed to introduce a resource that would be attractive to the half-shell trade during the spawning season. The
first commercial quantities of triploid C. gigas spat were produced in 1984, and the first harvest of market-size oysters
has a high consumer acceptance and that the substitution of
triploids for diploid C. gigas is an effective resource management tool (Jim Donaldson, Coast Oyster Co., Quilcene,WA, pers. commun., Oct. 1986).
Other examples of genetic manipulation of mollusks
include the production of disease resistance in oyster populations and the genetic selection of shell markings for the
production of identifiably distinct clams for restocking programs. The outbreak of MSX (Halplosporidium nelsoni) andsubsequent decline of the oyster fishery in Delaware Bay inthe 1960s prompted the establishment of a breeding program
to produce disease-resistant oysters. The project has selected
for MSX-resistant survival for several generations and has
produced oysters for restocking that are many times moreresistant than natural stocks (Ford and Haskin 1982). The
general interest in restocking programs by management agencies has led to the production of seed with external characteristics allowing the easy identification or segregation of
introduced populations. An obvious question applied to stocking programs is their real value in the contribution to thecommercial or recreational harvest. Without a mechanism
to identify the stocked populations, the actual contribution
can only be speculated. In South Carolina, a project has been
initiated to determine the benefits of restocking public shellfish grounds with hard clam, Mercenaria mercenaria. In
order to determine the impact of such stocking programs andallow comparisons between introduced and native populasions, it was necessary to provide seed stock distinguishable
from the native population. This was accomplished by crossing local clams with the "notata" variety of the same species.
This variety has alternate bands oflight and dark on the shell,
making it easily differentiated from native stock. The shellmarkings have been demonstrated to be controlled by a single
gene, or several closely linked genes, inherited as a Mendelian unit (Chanley 1961, Humphrey and Walker 1982). The
seed generated through this cross has a very high percentage (80%) of notata coloration and will thus be segregatable from native wildstock which typically has less than 1%of the total population displaying notata markings.
A final example of genetic manipulation in molluscan fisheries is the recent work with heterozygosity in marine bivalve
populations. Several reviews have brought considerable
attention to the relationship between multiple-locus enzyme
heterozygosity and growth rate (Koehn and Gaffney 1984,
Gaffney and Scott 1985). Additional research has implcatedimproved survival and/or vigor with increasing heterozy-eries on the eastern seaboard. In these fisheries, shellfish seed
are taken from public or privately owned seed beds to areas
where recruitment is low but growth and survival are excellent. The seed beds are restocked annually with shell orother cultch, normally at a time when shellfish are setting,to replenish the set and seed for future transplants.
In the northeastern United States hard clam seed is often
planted by townships to augment natural clam populations
and improve recreational and commercial fishing. As examples, townships in Massachusetts and New York typicallypurchase 4-6 mm seed clams from commercial hatcheries
and utilize field nursery systems (rafts, cages, etc.) to growthe seed out to planting size (20-25 mm). These programs,
however, are limited by the length of time available for effective field nursery culture and the availability of suitablesize seed in the early spring. Recently, at least one townshipin New York (Brookhaven) has begun buying young postset
clams (0.5 mm) and using a land-based upflow nursery to
produce the 5-mm seed for their field nursery system. Overall, the seed planting programs of the Northeaster UnitedStates are relatively small, and their value to the fisheries
they were implemented to augment is questionable. A thorough evaluation of the planting programs has not been performed, and the factors influencing the potential success ofsuch programs are not well understood.
In an analysis of two planting programs in New York and
Massachusetts, Malouf (1989) concluded that clam seedplanting programs of undetermined value should not be considered as benign at worst. These programs can result in theneglect of other management tools, the introduction of diseaseorganisms or exotics, the possible reduction of genetic variability in natural stocks, and the possible degradation of
growth rates and survival in natural populations by exceeding the carrying capacity of local environments. While it ispresently difficult to justify the use of hatcheries to bolster
declining commercial landings, it does appear that hatcheries
can play a proper role in molluscan fishery management.
Malouf (1989) stated that, as part of an integrated management program with realistic goals, hatcheries and other culture systems can be used to help establish or reestablish selfsustaining populations in localized areas, sustain recreational
fisheries in intensively harvested areas, and provide a mechanism for allowing the genetic improvement in fishery stocks.

Genetics in molluscan fisheriesenhancement_

Aside from the obvious benefits of improving growth andsurvival of molluscan stocks through genetic intervention,
manipulation of the genetic architecture of molluscan populations can provide tools of significant value to fishery management. A good example is the recent development of
triploid Crassostrea gigas and their incorporation into the
Pacific oyster fishery of Washington State (Chaiton and Allen
1985). Although it appears that triploidy does not impart
significantly faster growth in oyster seed (Stanley et al. 1981),
it does interfere with gametogenesis, resulting in functionally55

Chaiton, J.A., and S.K. Allen
1985 Early detection of triploidy in the larvae of Pacific oysters,
Crassostrea gigas, by flow cytometry. Aquaculture 48:35-43.
Chanley, P.E.
1961 Inheritance of shell markings and growth in the hard clam, Venus
mercenaria. Proc. Nat\. Shellfish. Assoc. 50: 163-169.
Chew, K.K.
1979 The Pacific oyster (Crassostrea gigas) in the West Coast of theUnited States. In Mann, R. (ed.), Exotic species in mariculture.
Mass. Inst. Techno\. Press, Cambridge, 249 p.
Dillon, R.T., Jr., and J.J. Manzi
1987 Hard clam, Mercenaria mercenaria, broodstocks: Genetic drift
and loss of rare alleles without reduction in heterozygosity. Aquaculture 60:99-105.
1988 Enzyme heterozygosity and growth in nursery populations of
the hard clam, Mercenaria mercenaria. J. Exp. Mar. Bio\. Eco\.
116:79-86.
Dow, R.L.
1953 An experimental progrma in shellfish management. Fish. Circ.
10, Maine Dep. Sea Shore Fish., Augusta, Me, II p.
Dugas, R.
1984 New findings may spur state's oyster production. Louisiana
Conversationists, Nov-Dec, p. 4-7.
Ford, S.E., and H.H. Haskin
1982 History and epizootiology of Haplosporidium nelsoni (MSX),an oyster pathogen in Delaware Bay, 1957-1980. J. Invertebr.
Patho\. 40:118-141.
Gaffney, P.M., and T.M. Scott1985 Genetic heterozygosity and production traits in natural and hatchery populations of bivalves. Aquaculture 42:289-302.
Humphrey, C.M., and R.L. Walker
1982 The occurrence of Mercenaria mercenaris form notata in Georgia
and South Carolina: Calculation of phenotypic and genetypic frequencies. Malacologia 23(1):75-79.
Kassner, J., and R.E. Malouf
1982 An evaluation of "spawner transplants" as a management toolin Long Island's hard clam fisheries. J. Shellfish REs. 2(2):165-172.
Koehn, R.K., and P.M. Gaffney
1984 Genetic heterozygosity and growth rate in Mytilus edulis. Mar.
Bio\. 82:1-7.
Mackenzie, C.L., Jr.
1979 Management for increasing clam abundance. Mar. Fish. Rev.

gosity (Rodhouse and Gaffney 1984). These data have stimulated the initiation of a breeding program to improve growthand survival in hatchery-reared populations of the hard clam,
M. mercenaria, in South Carolina. This program incorporates three breeding schemes to produce improved stocks:
Hybridization (with M. campechiensis), selected breeding,and outcrosses of inbred lines to induce increased enzymelocus heterozygosity. The lines produced through these outcrosses performed better than parental lines in overall growthover the first 12 months of culture but have not demonstrated
increased heterozygosity. When compared with corresponding wild populations in regard to allele frequencies at sevenpolymorphic enzyme loci, the outcrossed lines showed evidence of genetic drift and loss of rare alleles. These crosses
obviously resulted in the production of fast-growing linesthat were genetically distinct from the parental stock (Dillon
and Manzi 1987). Further analysis indicated that there werehighly significant differences at individual enzyme loci inthe largest and smallest clams from each cross (Dillon andManzi 1988). These results would be consistent with the
hypotheses that the alleles themselves were not effecting
growth or were related to linkage disequilibrium. It appears
instead that alleles are marking the entire parental genone,
and that variation in growth rates of offspring from individual
parents are masking a possible relationship with overall
heterozygosity. This work is increasing the understandingof genetic variation in hatchery-reared seed and may allow
more efficient and better-directed breeding programs for the
production of molluscan seed stocks.

Summary_

Through the use of case histories and reviews of recent andongoing research programs, this survey provided a brief
recapitulation of the use of aquaculture, particularly hatcheries and genetic manipulation, in molluscan fisheries management. In summary, aquaculture-related fisheries management activities have significant potential for the mollusk
fisheries of North America. Concentrating management programs in these activities can, however, result in neglect ofother management tools and can lead to reduction of genetic
variability in natural stocks and the possible degradation of
growth rates and survival in local natural populations whenintroduced stocks exceed environmental carrying capacities.
As part of an integrated fisheries management program,aquaculture can provide significant latitude in management
options and can provide mechanisms for realistic stock improvements in fishery populations.

Citations41(10): 10-22.

Malouf, R.E.
1989 Hatcheries as a management tool in clam fisheries. In Manzi,J., and M. Castagna (eds.), Clam mariculture in North America, p.
448-461. Elsevier Sci. Pub\., Amsterdam.
McHugh, J.J.
1981 Recent advances in hard clam mariculture. J. Shellfish Res.
1(1):51-56.
Reisinger, A.E., Jr.
1978 Demonstrate revitaIization of oyster beds by resurfacing and reseeding. Fourth quarter and summation report, Contract 10740077, Coastal
Plains Reg. Comm., Coastal Resourc. Div., Brunswick, GA, 25 p.
Rodhouse, P.G., and P.M. Gaffney
1984 Effect of heterozygosity on metabolism during starvation in theAmerian oyster, Crassostrea virginica. Mar. Go\. 80:179-187.
Stanley, J.G., H. Hidu, and S.K. Allen
1981 Polyploidy induced in the American oyster, Crasstrea virginica,
with cytochalasin B. Aquaculture 23: 1-10.
Tarver, J.W., and R.J. Dugas
1973 Experimental oyster transplanting in Louisiana. Tech. Bul\.
7, Louisiana Wild\. Fish. Comm., New Orleans, 6 p.
Turner, H.J., Jr.
1951 Third report on investigations of methods of improving theshellfish resources of Massachusetts. Report to the Committee ofClam Technicians, Atlantic States Marine Fisheries Commission. Contrib. 564, Woods Hole Oceanogr. Inst., Woods Hole, MA, 5 p.

_

Beaven, G.F.
1953 A preliminary report on some experiments in the production
and transplanting of South Carolina seed oysters to certain watersof the Chesapeake area. Proc. Gulf Caribb. Fish. Inst. 5: 115-122.
Bricelj, V.M., and R.E. Malouf
1981 Aspects of reproduction of hard clams (Mercenaria mercer.'llria)
in Great South Bay, New York. Proc. Natl. Shellfish. Assoc. 70(2):216-229.

56

Application of LHRH-a
Cholesterol Pellets toMaturation of Finfish:
Milkfish

It has become essential in current aquaculture practice to control the reproductive cycle of cultivated fish in captivity. The
traditional method of collecting fry from nature for aquaculture purposes is gradually being replaced by productionof fry in the hatchery. Another objective of hatchery fry
production is for release into the ocean for stock enhancement or for ocean ranching, as in the case of salmon andmany species cultured in Japan. These goals depend on the
successful maturation and spawning of adult fish in captivity,
as well as on larval rearing. Unfortunately, these processes,
particularly spawning, occur sporadically in most cultured
species.
The purpose of induced spawning is to bring about the [malstage of maturation in both males and females. In males, thisstage includes spermiation and ejaculation. In females, it
includes the migration and breakdown of the germinal vesicle, hydration, ovulation, and oviposition. Many researchers
have reviewed the techniques currently used to induce spawning (Harvey and Hoar 1979, Lam 1982, Donaldson andHunter 1983, Scott and Sumpter 1983, Lam 1985). Successful spawning can be achieved in most cases by a variety ofmethods including the use of hormones. After fertilized eggs
are obtained, larvae are hatched and reared in a hatchery.
The standard procedure for larval feeding begins withrotifers, brine shrimp, and/or copepods and is followed bya formulated feed. These procedures were reviewed by
Kuronuma and Fukusho (1984) and Fukusho (1985).
Spawning can be induced and viable larvae produced only
after the fish reach a certain stage of maturity. Some fish
species, however, either do not complete or even begin
maturation in captivity. Techniques for inducing maturation
are still under development.
Induced maturation requires a more prolonged period(weeks to months) of hormone therapy than induced spawning. Hormone therapies are used to induce maturation by
overcoming the physiological barriers posed by lack ofnecessary environmental stimuli. Environmental cues are
known to play an important role in regulating reproduction
and mediating the secretion of hormones which synchronize
the activities of various organs into an orchestrated physiological and biochemical response. An effective hormone
therapy must combine the most productive hormone formulation with the proper administration strategy. Among theavailable hormones and methods, LHRH, incorporated ina cholesterol pellet for implantation, has attracted increased
attention (Donaldson and Hunter 1983, Crim 1985, Lam
1985).
In this report, we discuss the technologies for administering LHRH and document its potency for advancing andaccelerating maturation and the reproductive cycle and forsynchronizing spawning of various fish species. Finally,
milkfish will be used to illustrate the potency of LHRH-ain inducing the maturation and spawning of important
cultured fish.

CHENG-SHENG LEE
CLYDE S. TAMARU
Oceanic Institute
Makapuu Point
Waimanalo, Hawaii 96795

ABSTRACTOne step toward the goal of stock enchancement of a particularspecies is the control of its maturation in captivity. Many cultivated finfish species, however, do not complete the reproductive cycle in captivity. Hormone therapies have been used toovercome the physiological barriers that inhibit completion of
the reproductive cycle. Acute or chronic hormone administration is often used to deliver various hormones or steroids to thefish. The slow and sustained release of LHRH to trigger thesecretion of endogenous hormones is one hormone therapy attracting more attention.
The application of LHRH and its analogues and their potency
for manipulating the reproductive activities of various fish,
especially milkfish (Chanos chanos) , is documented in thisreport.

57

Administration of LHRH

Table 1
Structure of LHRH.

_

Modes of administration also affect the potency and half-lifeof LHRH in the fish. Crim (1985) discussed different administration methods, and other experiments were conductedto compare different application strategies (CTHAP 1977
Weil and Crim 1983, Kouril et al. 1983). LHRH/LHRH-~
c~n be delivered to the fish at different body sites and using~Ifferen~ vehicles. Injections can be made intracranially,
mtrapentoneally, and intrapericardially or intramuscularly.
CAHEF (1975) indicated that effective dose of LHRH in
most cultured carp species was lower when delivered byintracranial injection than with intraperitoneal of intramuscular injection. Only slightly better results were found withintracranial injection than with intraperitoneal injection for
inducing ovulation in goldfish (Lam et al1976). Kouri! et al.
(1986) conducted experiments with tench (Tinea tinea) andfound that there was no difference in the number of spawned
fish between intrapericardial and intramuscular injection of
LHRH-a.
The vehicle used to deliver hormones to fish determines
the rates of release and diffusion of the hormones and, consequently, the release and diffusion rates of gonadotropin.
LHRH and its analogue have been administered to fish ineither liquid or solid form. The liquid form consists of LHRH
disso~v~ in ?8% NaCl solution or in 40% propylene glycol.
AdministratIOn of this form results in a rapid initial increaseof the circulating hormone level but it is not sustained. Aidaet al. (1978) prolonged the release of LHRH for a few days
by using a viscous liquid vehicle. They prepared an emulsified solution of synthetic LHRH in Freund's adjuvant.
Administration of the hormone in solid form sustains hormone release from weeks to months. Chronic LHRH administration devices have been prepared in the form of either
a silicone rubber implant or cholesterol pellet. Both methods~Iiminate the need for frequent injections, thereby decreasmg stress.
Preparation of LHRH silicone rubber implants has been
descr~bed by Lotz and SYllwasschy (1979). Kent et al. (1980)
descnbed a cholesterol matrix pellet suitable for delivery of
LHRH-a. This method was further modified by Lee et al.
(1985, 1986c) to meet specified experimental needs. The
basic composition of the LHRH-a cholesterol pellet is 95 %cholesterol, 5% cocoa butter, and approximately 1% of theabove total as LHRH-a. Following the procedures establishedby Lee et al. (1986b), each pellet weighs 20 mg, measures
2.4 mm in diameter and 5.0 mm in length, and contains 200
Jig LHRH-a. A bioassay study on this pellet was conducted
on trout by Dr. L.W. Crim (Memorial Univ., Newfoundlan~, Canada). Pellets were implanted intraperitoneally (IP)or mtramuscularly (1M) in rainbow trout. Blood from eachfish was sampled on day 1 (the day of implantation) and again~t I, 2, and 4 weeks after implantation. Gonadotropin levels
m blood serum showed a rapid elevation and remained at
a higher level than in the control group for up to 4 weeks(Fig. 1).

pGlu-His-Trp-Ser-Tyr-Gly-Leu'-Arg 8-Pro-Gly-NH 1
Mammalian LHRH
pGlu-His-Trp-Ser-Tyr-Gly-Trp'-Leu 8-Pro-Gly-NH1
Salmon LHRH

Luteinizing hormone-releasing
hormone (LHRH) - - - - - - - - - The hypothalamus-pituitary-gonad axis is known to be theneuro-endocrine control route for fish reproduction (Donaldson 1973, Lam 1985). The hypothalamus controls the secretion of gonadotropin-releasing hormone (GnRH) which actson the pituitary, causing it to release gonadotropin. Activities in the hypothalamus are controlled by environmental~d/or ~o~onal factors, a process which usually takes a longtime to lrutiate. Theoretically, direct administration of GnRH
should shorten the time required to release gonadotropin.
Research has been conducted to identify the structure of
GnRH in fish (Sherwood et al. 1983, 1984). These researchers concluded that mullet, rni1kfish, trout, and salmon all con~in chromatographically and immunologically identical peptides (Table 1). The structure differs from porcine (Matsuo
et al. 1972) and ovine (Burgus et al. 1972) LHRH in two
amino acids in positions 7 and 8 ofthe decapeptide (Table 1).
LHRH has since been synthesized in the laboratory, basedon this proposed structure, and has proven effective instimulating the release of gonadotropin and in inducing ovulation in mammals, chickens, and amphibians (see review by
Lam et al. 1976).
Although LHRH was first proven to stimulate the secretion of gonadotropin in the common carp, Cyprinus carpio(Breton and Weil1973), its potency is many times less than
the synthetic nonapeptide LHRH (CTHAP 1977). Chinesescientists were able to induce ovulation in cultured carpwith synthetic LHRH analogue. Several types of LHRH-a
are available and have been tried on fish. These include
des-GlylO[D-Ala6]-LHRH ethylamide; des-GlylO[D-Leu 6]LHRH ethylamide; des-BlylO[D-Ser(Bu t )6]-LHRH ethylamide; des-GlylO[D-Trp6]-LHRH ethylamide and des-GlylO[D-Phe6]-LHRH ethylamide. From an in vitro study conducted by Coy et al. (1975), luteinizing hormone (LH) andfollicle-stimulating hormone (FSH)-releasing activities of the
LHRH-a are ten times that of LHRH. The analogues also
have a longer half-life due to a slow rate of enzyme degradation (Buckingham 1978). Marks and Stern (1974) also ~tatedthat des-GlylO[D-Ala6]-LHRH ethylamide is less readily
broken down by brain enzymes than LHRH.

58

The potency of LHRH-a, when used to accelerate thematuration process, is inconsistent among species. LHRH-a
has been successfully used to induce ovulation and spawning, however, in many fish species. These include:
Acipenseridae (Doroshov and Lutes 1984); Anguillidae(Research Group of Eel Reproduction 1978); Cyprinidae(CTHAP 1977); Mugilidae (Lee et al. 1987); Plecoglossidae(Hirose and Ishida 1974); Serranidae (Barnabe and BarnabeQuet 1985, Harvey et al. 1985); Siganidae (Harvey et al.
1985); and Soleidae (Ramos 1986). Spawning success was
improved, however. by combining LHRH-a with otherovulatory agents such as: carp pituitary for mullet (Lee etal. 1987); 17 a-hydroxy-20[3-dihydroprogesterone for carp
(Breton et al. 1983), coho salmon and rainbow trout (Jalabert et al. 1978); and pimozide for goldfish, common carp,
trout, catfish, and loach (see review by Lam 1985).
Pimozide potentiates the ovulatory effect of LHRH-a byblocking the action of dopamine which can mimic gonadotropin-releasing inhibitory factor (GnRIF). Pimozide caneither be administered with LHRH-a or separately to the recipient fish. Billard et al. (1984) preferred to apply pimozide
prior to LHRH. Sokolowska et al. (1984), however, concluded that the occurrence of ovulation in goldfish was highwhen pimozide was injected prior to or in conjunction with
injections ofLHRH-a. De Leeuw et al. (1985) indicated thatthe minimum effective dosage for inducing ovulation in
African catfish could be as low as 5 mg pimozide combinedwith 0.05 mg LHRH-a per kg body weight. Lin et al. (1985)
and Billard et al. (1984) have also conducted dose-response
studies on pimozide and LHRH-a used to induce spawningin loach and brown trout.
Studies on the use of LHRH-a for fish reproduction have,thus far, concentrated on freshwater species. Recently, a
research group at the Oceanic Institute in Hawaii has attempted to control the reproduction of milkfish, Chanoschanos, a euryhaline fish, by application of LHRH-a.

14.0
Control Sham

12.0

10.0

E

!

0
0

1M

100 .ug

200.u9IP

Chinese D-Ala

LHRH

EI 1M
8.0

~ IP

c

·Ci
~

0

6.0

"~
0

"

4.0

2.0

0
*124

* day 1*124

* 1 24*124

Elapsed Time (weeks)

Figure 1
Gonadotropin levels in trout after receiving a sham pellet or LHRH-apellet.

LHRH and the reproductive
cycle in fish_

Although LHRH did not elicit any change in prespawninglandlocked salmon's pituitary GtH content (Weil and Crim
1983), LHRH and its analogue have proven effective inincreasing plasma GtH levels in many other fish species (seereview by Lam 1982, Donaldson and Hunter 1983). Elevation of the GtH level results in maturation and spawning offish. Many researchers, therefore, began using LHRH-a toreplace conventional HCG and fish pituitary. The responseof fish to LHRH-a varies, however, according to the stageof gonadal development at which the fish receives the hormone (Crim et al. 1983a). In prespawning salmon, ovulation and spermiation were accelerated by LHRH-a treatment,
but in sexually regressed male salmon, spermatogenesis was
not induced by the same treatment. The LHRH-a treatment
accelerated vitellogenic development during the rapid phaseof gonadal recrudescence, but reduced the GSI value in malesalmon. Crim and Glebe (1984) induced early spawning in
30% of the female Atlantic salmon given LHRH-a 45 days
prior to the normal spawning season, and in 94 % of thefemales treated 28 days before. LHRH-a cholesterol pellet
treatment did not result in accelerated maturation or spawning in grey mullet when given approximately 60 days prior
to the spawning season (Lee and Tamaru 1988). Ovulationin spring-spawning rainbow trout was advanced by 3 to 4
weeks, however, when fish were implanted about 2 months
before the spawning season (Crim et al. 1983b). The spawning season in sea bass was advanced by 40 days using an
LHRH-a injection under natural conditions (Barnabe andBarnabe-Quet 1985).

LHRH-a and milkfish
reproduction_

Maturation
The milkfish, an important food fish in Southeast Asia,
especially in the Philippines, Taiwan, and Indonesia, rarely
matures and spawns in captivity. Development of a reliable
method for controlling maturation and spawning in milkfish
has been investigated for a number of years (Lam 1984, Kuo
1985). The problems remain unsolved, however. Recent
studies carried out by Lee et al. (1986a,b,d) indicate that
LHRH-a has a positive effect on both maturation and spawning in milkfish.

59

100

Crystalline

Control

100

Testosterone
01
<:

-'"
~

::l

u.

'0

9/12

D Treatment 2

60

4/8

0
40

100

CD
01

'"
::

80

7/10

:::!:
.s::
(I)

D Treatment 1& LHRHa
50

DControlLiquid Testosterone

LHRHa& LHRHa

20

C

9/10

CD

50

CD

0-

Jan

8/8

0

:>

u,

'<

Mar

Apr

May

Jun

Jul

Aug

% Maturation Male (1986)

c... c...

s:: <:c... c...=.

III

Feb

<:

::l

::l

=.

Figure 3
Maturation of male milkfish in control and treatment groups during1986 season.

MonthsFigure 2
Percentage of fish that reach maturity in response to different hormone
therapies. Solid bar indicates females; blank bar indicates males. Fractions represent the number of mature f'lSh to the total number of sexed
fish. (Condensed from Lee et al. 1986b).

In the LHRH-a and liquid MT therapy, two mature females
were also found in the month of April. The number of mature
females increased steadily during the course of the experiment. By July, almost 90% of the individuals were foundto be mature.
When LHRH-a was combined with MT in crystal form,a high percentage of running ripe males were found by June.
A relatively low number of mature females was found in thisparticular hormone therapy. Overall, 65 % of individuals
undergoing this treatment matured by the end of July (after
4 months of treatment). Only one female from the control
group reached maturity (possessed 0.7 mm oocytes) during
the course of the experiment, attaining this state in July. Fourmales were found to possess milt as early as April. This
number declined steadily until the month of July, when there
was a dramatic increase. Therefore, the combination of
LHRH-a pellet with liquid MT capsules appeared to enhance
the maturation of milkfish.
In order to validate the effectiveness of LHRH-a pellets
and liquid MT capsules, this combined hormone therapy wasapplied to 80 fish beginning in March 1986 (as Treatment
1) and in April (as Treatment 2). The 20 other fish in thisstudy received placebo implants and served as controls.
Maturation of males was not significantly enhanced by thishormone therapy (Fig. 3). By June, however, 90% of thefemales possessed eggs larger than 50 IJm compared with
about 35 % in the control group (Fig. 4). These results
demonstrated that a combination ofLHRH-a pellet and liquid
MT capsule will enhance the maturation of female milkfish.

As mentioned, induction of the maturation process requires
a prolonged period (weeks to months) during which circulating levels of the desired hormone must remain elevated.
Among the varous methods of administration, the LHRH-acholesterol pellet has accelerated the reproductive cycles oflandlocked salmon (Crim et al. 1983a), rainbow trout (Crimet al. 1983b), and Atlantic salmon (Crim and Glebe 1984).
In our 1985 milkfish maturation study, LHRH-a cholesterolpellets were applied alone or in conjunction with 17a-methyltestosterone. The three hormone therapies used were: Cholesterol pellets containing 200 IJg of LHRH-a (LHRH-a pellet)
or combinations of LHRH-a pellets plus silastic tubing containing either 250 IJg of dissolved 17a-methyltestosterone(liquid MT capsule) or 10 mg crystal 17a-methyltestosterone(crystal MT capsule).
Experimental groups of 20 milkfish each received one ofthese three therapies beginning in March, while a fourth control group received placebo implants. LHRH-a pellets wereadministered monthly; crystal MT capsules were administered once; and liquid MT capsules were administered
twice, at the beginning of the experiment and three months
later. The application of the LHRH-a pellet alone was lesseffective in inducing maturity in males but appeared toenhance the total number of females that reached maturity(Fig. 2). Mature females were found as early as April. The
combination of LHRH-a and MT, in either crystal or liquid
form, resulted in a significantly higher number of matureindividuals by the month of July when compared with allof the other treatments (Fig. 2).

60

100

I---- P e l l e t s _ I __> - - -o Control

10

D Treatment 1
80~Response[;] Treatment 2

",.

60

In 8
Q.
E

0

No Response

~

:( 6
40

-,""'

4

OJ

.Q

E

20

::l

.;...~:

Z

:> N

2

rLi-...L.J..£~.·.;LJ··--LI1L.l...I:J.;U..--l...Uil[(:o L-..--_ _-----LJ
Jan

Feb

Mar
Apr
May
Jun
% Maturation Female (1986)

o

Jul

Apr

Ma y

Jun

Jul

Aug

Sept

Oct

Nov

Months (1985)

Figure 4

Figure 5

Maturation of female milkfish in control and treatment groups during1986 season.

Frequency of successful and unsuccessful induced spawnings of milkfish, attempted April-November 1985. Two strategies were employed
in inducing fmal maturation and spawning: 1) LHRH-a cholesterol pellet
implants, and 2) LHRH-a liquid injections. (From Lee et al. 1986b).

Spawning
The formulation ofa standardized method to induce milkfish
to spawn has eluded investigators for over a decade (Lam
1984, Kuo 1985). Initially, spawning attempts involved administering piscine pituitary extracts (salmon or carp), plus
HCG (Vanstone et al. 1977, Juario et at. 1979, Kuo et al.
1979, Liao et al. 1979). More recently, HCG has been usedalone to bring about the final maturation of ova (Tseng andHsiao 1979; Lin 1982, 1984). In all previous attempts,
however, fertilized eggs were obtained by manual strippingof both females and ripe males for their gametes. This action usually resulted in the loss of broodstock, in only a single
spawning per season, and in a low fertilization rate (0-60%).
These factors clearly underscore the need for a more reliable
method of inducing milkfish to spawn. This method should
insure a higher fertilization rate, survival of spawners after
spawning, and plUltiple spawnings.
In many cultured species, LHRH/LHRH-a has been used
to replace traditional ovulating agents such as HCG or piscine
pituitary (see review by Donaldson and Hunter 1983). We
therefore evaluated the effectiveness of LHRH-a as a spawning agent for milkfish, when administered in either pellet
implants or injections. Induced spawning was attempted whena female possessed an average egg diameter of 650 lAm or
more. The maturity of males was assessed by exertingpressure on the abdomen and observing whether or not milt
could be extruded. In each spawning attempt, LHRH-a was
only administered once through either intramuscular pellet
implantation or injection, in contrast to two or more injections in conventional spawning trials. A fixed dose of 250
lAg per fish was administered to all females and males receiving hormones. Control fish were either injected with normal
saline or not treated at all. A total of 50 induced spawning
attempts was conducted using either intramuscular pellet
implatation (N= 17) or injection (N=33). LHRH-a pellets
were used April-July, and LHRH-a injection trials were

10

8
In

c;

~Responseo

No Response

E
~ 6

:(

'0
OJ

.c

4

g

Z

2

o L-..-"'-c::-"'-c::-"'-c::-.L...-PI
700-750PI
750-800PI
800-850PI
850-900PI
900-950

Eg9 Diameter ().1m)

Figure 6
Number of successful and unsuccessful induced spawns versus average
egg diameters at which hormonal therapies were initiated. Results
are presented for two different modes of administration (p=pellet,
I=injection). (From Lee et al. 1986b).

conducted July-November (Fig. 5). Overall, a 53 % spawning success rate was obtained using the pellet implant as aspawning agent. The fish consistently spawned about 48
hours after being implanted. Nineteen of 33 attempts using
LHRH-a administered via an injection resulted in successful
spawnings (58 % success rate). In contrast to those inducedwith pellets, successful spawnings from fish injected with
LHRH-a occurred within 20-26 hours after receiving theirinjections.
The number of successful spawnings is related to the average size of eggs at which the LHRH-a was administered (Fig.
6). The number of successful spawnings appears to increase
with size of initial egg diameters, and 700-950 lAm is the
optimal range. Successful spawnings occurred in fish that61

Citations

possessed single modal distribution of egg size in some fishthat possessed bimodal distributions. In the latter case, thesmaller clutch of eggs did not exceed 350 ,.an in size. Spawning attempts in fish that possessed bimodal distribution ofegg sizes, where the smaller clutch exceeded 350 J-lill, did
not succeed.
In the above experiment, the dosages of LHRH-a per
kilogram body weight in spawning attempts were 41 .3 J-Ig
for pellet implantation and 58.7 J-Ig for liquid injection. Experiments are in progress to determine the minimum effective dosage for the spawning of milkfish.
In summary, LHRH-a is a potent hormone for controlling
the reproduction activities of many finfish species. These
activities include advancing and synchronizing spawning,
increasing milt volume, and inducing spermiation. LHRH-acholesterol pellets induce the release and sustain higher blood
serum levels of GtH. The proper combination of LHRH-acholesterol pellet with other hormones should control thematuration of most finfish species. This technology will
benefit the enhancement of natural populations and the initiation of ocean ranching.

Acknowledgments_

Aida, K., R.S. Izumo, H. Satoh, and M. Hibiya
1978 Induction of ovulation in plaice and goby with synthetic LH
releasing hormone. Bull. Jpn. Soc. Sci. Fish. 44:445-450.
Barnabe, G., and R. Barnabe-Quet
1985 Advancement and improvement of induced spawning in the sea
bass Dicentrarchus labrax (L.) using an LHRH analogue injection.
Aquaculture 49: 125-132.
Billard R., P. Reinaud, M.G. Hollebecq, and B. Breton
1984 Advancement and synchronization of spawning in Salmo gairdneri and S. trulta following administration of LHRH-A combinedor not with pimozide. Aquaculture 43:57-66.
Breton, B., J. Jalabert, K. Bieniarz, M. Sokolowka, and P. Epler
1983 Effects of synthetic LH-RH and analog on plama gonadotropin
levels and maturation response to 17 -hydroxy-20 -dihydroprogesterone. Aquaculture 32:105-114.
Breton, B., and C. Weil
1973 Endocrinologie comparee - effets du LH/FSH-RH synthetiqueet d'extraits hypothalamiques de carpe sur la secretion d'hormone
gonadotrophe in vivo chez la carpe (Cyprinus carpio L.). C.R. Acad.
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1978 The hypophysiotrophic hormones. Prog. Med. Chern. 15: 165198.
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1972 Primary structure of the ovine hypothalamic luteinizing hormonereleasing factor (LRF). Proc. Natl. Acad. Sci. USA. 69:278-282.
CAHEF (Conference on the Application of Hormones to Economic
Fish)1975 Experiment on induced spawning of farm fishes by synthetic
LRH. Kexue Tongboe 20(1):43-48.
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1977 A new highly effective ovulating agent for fish reproduction.
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Arimura1975 Stimulatory and inhibitory analogs ofLHRH.ln Motta, M., P.G.
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milkfish, p. 1-13. Oceanic Inst., Waimanalo, Hawaii, and Tungkang Mar. Lab., Taiwan.
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Crim, L.W., D.M. Evans, and B.H. Vickery
1983a Manipulation of the seasonal reproductive cycle of the landlocked Atlantic salmon (Salrno salar) by LHRH analogues administered at various stages of gonadal development. Can. J. Fish. Aquat.
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_

This research was supported by a grant from U.S. AID(DAN-4161-A-OO-4055-00). We wish to thank members of
the Finfish Program for their assistance in this research and
A. Belanger for preparation of the manuscript.

62

Lam, T.J., S. Pandey, Y. Nagahama, and W.S. Hoar
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13 p.
Kent, J.S., B.H. Vickery, and G.I. McRae
1980 The use of a cholesterol matrix pellet implant for early studies
on the prolonged release in animals of agonist analogues of luteinizing hormone-releasing hormone. Presented at 7th Int. Symp. on Controlled Release of Bioactive Materials, Fort Lauderdale, Florida.
Inst. Pharm. Sci. BioI. Stud., Syntex Research, Palo Alto, CA 94304.
KourH, J., T. Barth, J. Hamackova, and M. Flegel1986 Induced ovulation in tench (Tinea tinea L.) by various LH-RH
synthetic analogues: Effect of site of administration and temperature.
Aquaculture 54:37-44.
Kouri!, J., T. Barth, J. Hamackova, J. Sianinova, L. Servitova, J.
Machacek, and M. Flegel
1983 Application of LH-RH and its analog for reaching ovulation infemale tench, grass carp, carp and sheatfish. Bul. VU'RH Vodnany
2:3-16 [in Czech.].
Kuo, C.M.
1985 A review of induced breeding of milkfish. In Lee, C.-S., andI.C. Liao (eds.), Reproduction and culture of milkfish, p. 57-77.
Oceanic Inst., Waimanalo, Hawaii, and Tungkang Mar. Lab.,
Taiwan.
Kuo, C.M., C.E. Nash, and W.O. Watanabe
1979 Induced breeding experiments with milkfish, Chanos ehanos(Forsskal), in Hawaii. Aquaculture 16:247-252.
Kuronuma, K., and K. Fukusho
1984 Rearing of marine fish larvae in Japan. Int. Dev. Res. Cent.,
Ottawa, Ontario, Canada, 109 p.
Lam, T.J.
1982 Applications of endocrinology to fish culture. Can. J. Fish.
Aquat. Sci. 39: 111-137.
1984 Artificial propagation of milkfish: Present status and problems.
In Juario, J.V., R.P. Ferraris, and L.V. Benitez (eds.), Advancesin milkfish biology and culture, p. 21-39. Island Publ. House, Inc.,
Metro Manila, Philippines.
1985 Induced spawning in fish. In Lee, c.-S., and I.C. Liao (eds.),
Reproduction and culture of milkfish, p. 14-56. Oceanic Inst.,
Waimanalo, Hawaii, and Tungkang Mar. Lab., Taiwan.

63

Scott, A.P., and J.P. Sumpter
1983 The control of trout reproduction: Basic and applied res~archon hormones. In Rankin, J.C., TJ. Pitcher, and R.T. Duggan (OOs.),
Control processes in fish physiology, p. 200-220. Croom Helm,
London.
Sherwood, N.M., L. Eiden, M. Brownstein, J. Speiss, J. Rivier, andW. Vale1983 Characterization of a teleost gonadotropin releasing hormone.
Proc. Natl. Acad. Sci. USA, 80:2794-2798.
Sherwood, N.M., B. Harvey, M.J. Brownstein, and L.E. Eiden
1984 Gonadotropin-releasing hormone (Gn-RH) in striped mullet(Mugil cepha/us), milkfish (Chanos chanos), and rainbow trout (Sa/mo
gairdneri): Comparison with salmon Gn-RH. Compo Endocrinol.
55: 174-181.
Sokolowska, M., R.E. Peter, C.S. Nahorniak, C.H. Pan, J.P. Chang,
L. W. Crim, and C. Weil
1984 Induction of ovulation in goldfish, Carassius auratus, by pimozide and analogues of LH-RH. Aquaculture 36:71-83.
Tseng, L.C., and S.M. Hsiao
1979 First successful case of artificial propagation of pond-reared
milkfish. China Fish. 320:9-10 [in Chinese].
Vanstone, W.E., L.B. Trio, Jr., A.C. ViIlaluz, D.C. Ramsingill, S.
Kumagai, P.J. Duldoco, M.M.L. Barnes, and C.E. Duenas
1977 Breeding and larval rearing of milkfish Chanos chanos (Pisces:
Chanidae). SEAFDEC Res. Rep. 3, Southeast Asian Fish. Dev.
Cent., Philippines, p. 3-17.
Weil, C., and L.W. Crim
1983 Administration of LHRH analogues in various ways: Effect on
the advancement of spermiation in prespawning landlocked salmon,
Sa/rno sa/ar. Aquaculture 35: 103-115.

64

Trends in
Oyster Cultivationon the West Coast of
North America

Over the past 25 years dramatic changes in commercial oyster
operations have taken place on the west coast. The mostsignificant changes are centered around the procurement ofseed oysters and new innovations related to the developmentof desired stocks for cultivation. Further, although intertidal
bed culture is still the main growing technique utilized by
the oyster growers, we see an expansion of off-bottom
cultivation.
The main oyster produced on the west coast at the turnof the century was the Olympia or native oyster (Ostrea
lurida). With the decline of the native oyster industry, theeastern or American oyster (Crassostrea virginica) was
introduced for cultivation, primarily in the state of Washington. Survival was not good for this species and ultimately
the Japanese or Pacific oyster (Crassostrea gigas) was introduced and became the mainstay of the present west coastoyster industry. Aside from the Pacific oyster and, to alimited extent, the cultivation of the Olympia oyster in recent years, efforts have been made to utilize the Suminoe
oyster (Crassostrea rivularis) (Breese and Malouf 1977) for
cultivation primarily as a summer oyster. Also, efforts to
produce the Kumamoto variety of C. gigas for hatchery production have met with moderate success. Later activities
involved the growing of European oysters (Ostrea edulis)
and hybridized Miyagi and Kumamoto varieties of C. gigas
to produce what is called a gigamoto oyster. Althoughsmaller, the gigamoto will grow a deeper shell and provide
a good shape and taste for the half-shell market. Chew (1984)
discussed Pacific oyster production trends for Washington,
California, Oregon, and British Columbia and noted that
Washington is still the major producer for the west coast.
In fact, Washington's annual production has risen from over
6 million lbs (2722 MT) of meat in 1985 to 10 million lbs(4537 MT) in 1989. Recent estimates of 1989 production in
California are above I million lbs (454 MT), and British Columbia and Oregon are about 0.5 million lbs (227 MT) each.
Alaska has also begun production of Pacific oysters but at
a much lower level.

KENNETH K. CHEW
Division of Fishery Science and Aquaculture
School of Fisheries WH-10
University of Washington
Seattle. Washington 98195

ABSTRACT
Trends in oyster cultivation on the west coast of North America
are briefly discussed with comments on species utilized, culture
growout methods, remote setting of eyed larvae, and stock
development through genetics and breeding. Although several
species of oysters are utilized, the Pacific oyster (Crassostrea
gigas) constitutes over 98% of oysters produced on the west
coast.
Oysters are grown mainly on intertidal bed areas. OtT-bottom
culture, utilizing several techniques, is increasing but unlikely
to expand quickly because of permit-application requirements
related to the sociopolitical climate existing in most populatedareas of the United States.
The concept of remote setting of eyed larvae has been shownto greatly enhance seed production of Pacific oysters on the west
coast. Obtaining adequate Pacific oyster seed periodically fromnatural catches when available, backed up with a consistentannual catch from remote setting, makes seed production a concern of the past.
Stock development through genetics and breeding studies
shows the potential for developing stocks resistant to diseases,
as well as strains with desired traits. Breeding programs canbe developed to produce high summer carbohydrate levels inoysters. Essential safeguards against inbreeding problems are
discussed as they relate to Pacific oysters.
The method for producing the triploid oyster with greatly
reduced gonadal development in the summer is discussed. These
neutered oysters are expected to be in heavy demand for thesummer fresh and/or half-shell trade when regular production
is established.

Culture grow-out methods_

Extensive culture with Pacific oyster seed placed on intertidal beds for growout remains the major west coast production method, probably accounting for more than 90%, withthe rest produced by off-bottom culture.
Further, Crassostrea gigas probably constitutes more than
98 % of oysters produced on the west coast of the UnitedStates and British Columbia. Figure 1 provides a map of the
major areas of natural seed production and growout of commercial stocks from British Columbia south to California.
Although not shown, southeastern Alaska is also beginning
to produce Pacific oysters, primarily for the half-shellmarket.
65

Stake culture occurs in several areas. Wire or wood stakeswith seed-bearing cultch material attached to the top areplaced in the lower intertidal zone.
Pendrell Sound

Rack culture is one of the more popular type of off-bottom
cultivation. Racks are built in the intertidal zone and shell
strings are hung for production of oysters. This type ofculture is found in all four California areas in Figure 1 andis increasing in Willapa Bay and Grays Harbor, Washington. Alaska and British Columbia are also expanding thisculture technique.
Also, French plastic pipe collectors with seed can be used
in a type of rack culture in British Columbia and Washington.
Double rows of line are staked on the intertidal zone andthe plastic pipes are laid across and fastened to the line.

Lasqueti Island -------'t-----'
Barkleyof Sound-;======~~--.:~
StraitGeorQia
San Juan Islands --------t-:::O""'~:..J
PUQet Sound - - - - - - - - - \ - - - . : ; J . . . ' 1 'Hood Canal - - - - - - - - - \ - - - f A-Jf>Grays H a r b o r - - - -Willapa Bay ---------~ITi llamook B a y - - - - - - - - ' 7

Raft or floating culture The commercial use of rafts for
hanging oyster strings continuously in the water column was
initiated more than 20 years ago in southern Puget Sound,but has not expanded for a variety of reasons. Aside fromminimal biological concerns, there are problems with securing permits for such applications through governmental agencies. Generally, these problems relate to multiple-use conflicts, aesthetics, navigation, and environmental concerns,
all affecting the premit process.

PortlandYaquina Bay--------+

OregonCoos Bay - - - - - - - - - - - , s

Lantern and/or pearl nets Several operations in Washington and British Columbia utilize these types of hanging nets
on long lines or rafts to grow oysters for the half-shell trade.

Humboldt Bay - - - - - - - ; t . - E u r e k a

California

Trays Plastic netting is used in many areas along the west
coast for the production of single Pacific oysters and otherspecies for the commercial half-shell market. The methodof using Vexar plastic netting was adapted from the Frenchtechnique whereby sheets of material are folded over andsewn to make a basket. These baskets or trays are laid ona special metal or wood frame (rack) on the intertidal bed.
One of the major operations using this technique is in Willapa
Bay, Washington, and several other areas along the Pacificcoast are running tests to determine their feasibility.

Tomales Bay - - - - - - - Drakes Bay (Estero) - - - - - - " " - -Morro B a y - - - - - - - - - - - - - - - - \Remote setting for seed_

Figure 1
General area of Pacific oyster production.

In recent years Pacific coast hatcheries have become very
important to the oyster farmers. For many years, consistent
supply of seed oysters to maintain annual production wasdependent upon supplies from Japan, especially during thepost-World War II years prior to the 1970s. As Pacific oyster
seed shipments from Japan declined, natural catches of seedbecame available from some locations along the west coast(Pendrell Sound, British Columbia, and Hood Canal andWillapa Bay, Washington). Figure 2 summarizes in part theseed production for the state of Washington during the years
1947-85. As shown in this figure, most of the Pacific oyster
seed from Japan remained in the state of Washington. Although natural-caught seed may be available in Hood Canal,
it is not a dependable source of seed every year. For example, the two bays in north Hood Canal (Quilcene and Dabob

During the past 20 years, several methods of off-bottom
cultivation for Pacific oysters and other species have been
initiated. Each are briefly described below.

Long line culture involves the establishment of a system on
the intertidal beds where shell cultch material with seed isstrung between poles on heavy braided polypropylene rope.
This is a growing-culture operation at present and occurs in
Grays Harbor and Willapa Bay, Washington. Floating longline culture with buoys has been used in northern Puget Soundon a limited scale for hanging lantern and pearl nets for growing oysters.
66

C 100
A
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80
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50

55

60

65

80

70

85

LAFNAE.IN
WA.(EST.)

YEAR

Figure 2
Production of seed oysters in Washington compared with Japanese seed shipments to the U.S. Pacificcoast, 1947-85.

after 0-12 days in 5°C storage (Fig. 4), and was able to showthat the Pacific oyster eyed larvae should not be stored at
5°C beyond 8 days for best larval settlement or survival.

Bay) as a general rule will produce commercial quantities
of seed only six or seven years out of ten, a difficult situation for the oysterman who depends on this seed source.
A new culture technique has been recently initiated on thewest coast in which setting-size eyed Pacific oyster larvae
can be purchased from private hatcheries by the oyster
growers. The larvae can be kept alive for several days at
5°C in a cooler and sent great distances by air. Thus, theoyster grower can have a tank built on the farm and eyedlarvae ordered for settlement. Although this concept, referred
to as remote setting, has been tried experimentally for morethan 20 years, it did not become an economical and accepted
practice until 7-8 years ago. Presently two main hatcheries,
one in Oregon and one in Washington, produce over ten
billion eyed larvae annually to supply the needs of the west
coast growers who use remote setting to obtain seed. This
process was well described by Jones and Jones (1983). As
shown in Figure 2, there has been a dramatic increase ofover 80,000 cases of seed produced from hatchery eyedlarvae in 1985 alone, and over 100,000 cases annually sincethen.
In 1983 there were an estimated 18 oyster farmers building their own tanks to catch Pacific oyster seed fromhatchery-produced eyed larvae. Recent estimates show thatover 50 farmers from Alaska to California, including British
Columbia, are using remote setting to securing seed for theiroyster operations.
The cost of eyed larvae ranges from 8 to 12 cents/thousand depending on the time of year and the hatchery. Early
research by Henderson (1983) has shown the importance oftemperature and salinity for eyed larval settlement (Fig. 3).
As demonstrated in Figure 3, remote setting tanks shouldbe about 30°C and 30 ppt, respectively, for optimum results.
Henderson also ran tests to determine the percent settlement

40

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Figure 3
Cumulative mean percent larval Crassostrea gigas settlement at fivetemperature levels (15-35°C) and at five salinities (15-35'/00). Points
of intersection indicate factor interaction at the given coordinates.
(From Henderson 1983)

67

L-Dope and algal slurry to facilitate the remote setting ofPacific oyster .

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Stock development throughgenetic manipulation

According to Hershberger et al. (1984), two developmentsof Pacific oyster culture in the United States have made selection and direct breeding both feasible and attractive. First,
a successful artificial spawning technique for the Pacificoyster and development of a procedure for larval rearing provide the means to exercise control over the entire life history.
Recently, results from more detailed studies of conditioning and spawning procedures have identified several factorsthat can improve gamete quality (Lannan 980, Lannan et al.
1980, Muranaka and Lannan 1984) and, thus, predictablelarval production.
Secondly, Hershberger et al. (1984) indicated the technology of seed production in commercial oyster hatcheries had
developed to a point where their seed has become competitive(in terms of reliability and cost) with seed collected fromnatural production. It has only been within the past five years
that hatchery-produced spat of Pacific oysters has been in
demand by the oyster growers (Clark and Langmo 1979).
A systematic selection and breeding program has been
conducted with the Pacific oyster at the University of Washington for almost 15 years (Beattie et al. 1978, 1980; Perdue
et al. 1981; Hershberger et al. 1984). It was initiated during
the 1970s when there were major summer mortalities occurring along the Pacific coast which necessitated a look at thepossibility of breeding for a strain of oysters resistant to summer mortalities. Histological studies into the mortalities
revealed there was no identifiable pathogen that could beclearly related to the oysters dying in specific bays during
the summer. Detailed studies revealed mortalities may berelated to the gametogenic cycle and the physiological processes and stresses that take place during that time (Perdue
et al. 1981). Thus, several approaches were utilized during
the past 15 years at the University of Washington oyster
genetics program, focusing on three areas: 1 Survival during summer mortality, 2 genetic determination of carbohydrate (glycogen) content in relation to gametogenic cycles,
and 3 the effects of inbreeding.
During the past four years a new focus has been addedthe development of a triploid oyster. This was pursued
because of the need by oystermen for a summer oyster that
does not go through full gametogenesis. During the summer
months a normal diploid oyster will produce eggs or sperm
and become milky. Although edible, the product is aesthetically undesirable and in some cases unacceptable as ahalf-shell oyster. Thus triploidy has been looked upon as apotential for eliminating or reducing the incidence of gonadal
maturation in oysters, affectively neutering them for the fresh
oyster trade during the summer.

100

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Figure 4
Mean percent larval Crassostrea gigas settlement after 0-12 days in SoC
storage. Comparative mean spat survival after 90 days for each 48-hourstorage interval is displayed above. Vertical bars indicate standard errorof means. (From Henderson 1983)

This is basic background information, but the oyster farmer
will need to determine the requirements of his own system
to obtain best success.
Recent activities related to remote setting involves the useof the chemical L-3, 4-dehydroxyphenylalanine, commonlyreferred to as L-Dopa, which is also sold by one hatcheryselling the eyed larvae. L-Dopa is used to facilitate larval
settlement in the farmers' tanks. As a general rule, one can
expect between 20% and 30% of the eyed larvae to metamorphose and settle successfully. Discussions with several
oyster farmers reveal that a higher percentage is regularly
achieved.
After the larvae have settled, it is possible to feed themfor a day or two before they are taken from settling tanks
to the outside environment. Hatcheries also sell a concentrated algal paste or algal slurry (Krantz et al. 1982). The
algal cultures, usually made up of Tahitian lsochrysis or 3H(1halassiosira), are grown in large tanks and passed througha mechanical centrifuge for concentration into a paste. Thus,
the hatchery selling the eyed larvae can include sales of68Summer mortality
Adult
oysters

Although summer mortality has abated in recent years, theapproach utilized to study the problem and the breeding
program that evolved to attain resistant stocks are worth
reviewing. A major part of the early work on this problem
focused on identification of the agent responsible for mortality (Glude 1975). Studies in Japan concluded that thesummer mortalities were largely the result of physiologicalstress associated with highly eutrophic conditions (Koganezawa 1975). In both Japan and the United States, mortalities
were generally associated with areas of high productivity,
high nutrient level, and water temperatures exceeding 20°C,
coincident with a period of maximum gonad maturation (Perdue et al. 1981). Laboratory research demonstrated that massmortality approximating the characteristics of the naturalsituation could be induced by holding oysters in 20°C waterand increasing the nutrient levels (Lipovsky and Chew 1972).
Although studies by Grischkowsky and Liston (1974) demonstrated that Vibrio sp. may playa significant role in thelaboratory mortality tests, they do not appear to be a causative
pathogen under field conditions.
It should be noted that none of the early work in Japanon summer mortality included selective breeding as a method
to mitigate the severity of this problem. One has to recognizethat the initial information needed before conducting a selection and breeding program is to determine whether theorganism contains adequate genetic variability on which tobase the program; thus, genetic variability tests through electrophoretic analysis were conducted by Buroker et al. (1975).
Their study indicated a good selective breeding potential andled to a selection design and genetic analysis (Fig. 5) usedin breeding oysters for resistance to mortality during simulated summertime stress (Lipovsky and Chew 1972) toinduce a 60-70% mortality. Survivors were spawned andmated by crossing a single male with a single female toproduce experimental families. Progress in increasing
resistance in the families produced was measured by challenging offspring when they reached adulthood with the sameelevated temperature conditions. Results from selectedgroups were compared with those using an unselected andcontrol population to assess progress.
According to Hershberger et al. (1984), progeny from theinitial crosses performed in 1973 and 1975 indicated a goodpotential for development of oyster strains resistant to thermal stress (Beattie et al. 1978). Out of the seven families
originally tested, two consistently survived the thermal stresssignificantly better than the control groups and none of theselected families showed poorer survival. Thus, it appearedthat selection could be used to improve resistance to one factor involved with summer mortality, thermal stress.

.,,"Chcnenge"
Ihigh tempero1ur'e. with orwithout nutrient enri:tment l

,,-~

,

Progeny
testing,,,-' f~~~~~~j

Su~~~~~~g(G'~~

Analyze genetic
variability(~trophorelicanalysis)~~~~O:no~d-·:)wm...,./'

Progeny(seed fromsurvivor ll. survivod

9dFigure 5
Diagram of selection design and genetic analysis used in breeding oysters
for resistance to mortality during simulated summer stress (from Beattie
et aI. 1978 and Hershberger et aI. 1984).

Although laboratory tests proved that resistant strains canbe developed, it was necessary to field-test the various
families in areas of known summer mortalities. It was during this period, the mid-1970s, that the summer mortalities
abated. However, we were able to determine that, although
increased gonadal development was not directly related tohigh or low mortality, the timing of the mortality coincidedwith maximum gonad development (Perdue et al. 1981). Further, from testing the families when mortalities were still
occurring, it was discovered that those with higher survival
had consistently higher carbohydrate (glycogen) stored
energy reserves than oyster families with lower survival.
With this type of information, selected families with higher
glycogen levels as well as better shell growth were bred in
the hopes of developing an oyster with higher marketability.

Carbohydrate content
Carbohydrate (glycogen) is the major stored energy reservein oysters and during anaerobiosis is the only substrateutilized for metabolic processes (Hochachka and Somero
1973). In addition, it was pointed out by Gabbott (1975) thatgamete production occurs at the expense of stored glycogenreserves. This is the primary reason glycogen levels havebeen shown to be inversely related to gonadal development
in Pacific oysters (Matsumoto et al. 1934, Mann 1979,
Hershberger et al. 1984). Perdue et al. (1982) and Hershberger et al. (1984) indicated that heightened gonadal development has a major influence on susceptibility to summer
stress conditions and that carbohydrate content may be a more
precisely measured trait on which to base selection. Further,carbohydrate content is an important component of oyster
marketability. Immature or nonspawning (high glycogen content) oysters have a high market desirability compared with69

Triploidy
FAMILY A

FAMILY.

FAMILYC

FAMilY

0

Recent work by two researchers, Standish K. Allen and
Sandra L. Downing at the School of Fisheries of the
University of Washington, has shown conclusively that
triploid Pacific oysters can be produced as a viable commercial option (Allen 1986, Allen and Downing 1986, Downing and Allen 1987). Allen (1986) indicates that triploidy
has been produced in shellfish using three different methods:
Chemical, pressure, and thermal induction. All three affectinhibition of polar body development resulting in an additional maternal set of chromosomes. Allen pointed out that
all methods to induce triploidy depend upon absolute control of the moment of fertilization and subsequent meiotic
events in the egg. Since the rate of these events is temperature-dependent, reproducibility of induction proceduresin a given species will depend on maintaining constanttemperature during incubation. Studies by Downing andAllen (1987) clearly demonstrate the dependence of temperature on time in which treatment can take place. In theirstudies they use primarily Cytochalasin B (CB) to induce
triploidy. Although earlier work with hydrostatic pressure
has been shown to produce triploidy in Pacific oysters(Chaiton and Allen 1985), the results were not as good aswith CB.
Researchers Allen and Downing report that treatment
consists of adding 1 mg of CB dissolved in 1 mL ofdimethylsulfoxide (DMSO) to a liter of sea water containing fertilized eggs at the beginning of any treatment. After
15 minues, the eggs are filtered through a 25-l-lm screen andthen resuspending the zygotes in a 0.1 % DMSO bath foranother 15 minutes. During this time, egg suspensions are
stirred occasionally during the treatment and rinsed. Afterrinsing, zygotes are placed in appropriate tanks and reared
according to accepted procedures (Breese and Malouf 1975).
Studies by Downing and Allen (1987) demonstrate conclusively that the time and temperature of treatment application are very critical (Fig. 7). Each of the Roman numerals
in this figure represents 15-minute intervals after fertilization of the eggs and the time at which each individual test
on different lots were made. The fitted curves reveal thatthe triploid induction maxima at 18°, 20°, and 25°C were52, 76, and 90%, respectively. Also, lowering the temperature delays the induction peaks; maxima at 25°, 20°,and 18°C are approximately 30, 45, and 50 minutes postfertilization, respectively. Two private hatcheries are now
utilizing these techniques to produce triploidy Pacific oysters,
and both have them already available for the half-shell oyster
market, especially for the summer periods. Further, there
are now available a hatchery manual and accompanying video
by Allen et al. (1989) for producing triploidy oysters.

Figure 6
Rotational line-breeding plan which produces eight full-sib and four
half-sib families (from Hershberger et al. 1984).

mature oysters during peak gonadal maturation (low glycogencontent). Thus, selection and breeding to maintain high carbohydrate content could also improve the marketabilicy ofoysters (Hershberger et al. 1984). Over a ten-year period
the breeding program has provided lines with significantly
elevated carbohydrate levels, and are currently utilized forbroodstock for one company's production of gourmet oysters.
Preliminary results on the carbohydrate content of a seriesof selected families grown in different locations suggest there
is a major genetic component in the utilization of a glyc'Jgenduring gonadal development.

Inbreeding
Hershberger et al. (1984) discussed the effects of inbreeding in the University of Washington selection and breeding
program for oysters. They chose to avoid inbreeding depression by the use of a scheme of rotational line crossing, asystematic breeding design that minimizes the increase inlevel of inbreeding per generation (Fig. 6). In this rotational
design (produces eight full-sib and four half-sib families) the
increase in inbreeding coefficient is less than 0.01 per generation. Although this approach does not decrease the amountof inbreeding initially imposed by a small breeding population size, it does minimize the change across generations.
It should be noted that recent preliminary results from someof the family bred for high glycogen levels (Beattie et al.
1986) suggest inbreeding depression by exhibiting pcorer
shell growth. This is presently being addressed in our
breeding studies, and the success from using this breeding
design is still being assessed.

70

Concluding statement
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An attempt has been made to briefly summarize the recentchanges in oyster cultivation along the west coast of North
America. Although intertidal bed cultivation is still the mostimportant, attempts have been made to implement a variety
of off-bottom culture techniques in many select areas. Offbottom culture is growing, but continues to encounter difficulty because of permit application requirements related tothe sociopolitical climate existing in most populated areasin the United States. This is especially true for applications
for raft or floating type culture facilities.
There is no doubt that the new concept of remote settingof eyed larvae for Pacific oysters will grow. Less than 10
years ago the oyster farmer on the west coast still needed
to be concerned with getting adequate supplies of seedoysters. Now the natural catches in several areas, complemented by many farmers building setting tanks on their own
property to catch their own seed through remote setting, haveremoved this concern. In essence, some growers no longer
depend on natural catches because of remote setting for theirown seed. The cost is equivalent according to some growers.
Two hatcheries, Coast Oyster Hatchery in Washington and
Whiskey Creek Hatchery in Oregon, were expected to produce over 12 billion eyed larvae for sales or for their own
use in 1986 to satisfy the needs of the west coast industry.
There are other hatcheries in California and British Columbia, and one being proposed for Alaska.
Stock development through genetics and breeding studies
have been in existence on the west coast for more than 10
years. The University of Washington School of Fisheries has
been investigating summer mortalities of Pacific oysters in
the late 1960s and early 1970s and attempting to breed a resistant stock to this disease. No known pathogen was found consistently related to this summer kill. Further, studies strongly
suggested that the phenomenon was related to physiologicalstress related to the reproductive cycle. Stocks of oysters thatdied generally had lower carbohydrate (glycogen) levels.
With this in mind, a breeding program was established todevelop stocks with higher glycogen levels and including
an approach to minimize inbreeding problems. Althoughattempts were made to reduce this problem, early results
show continued breeding of summer oysters for high glycogen can also lead to oysters with slow shell growth. This
problem is presently being addressed at our experimental
hatchery.
The production of triploid Pacific oysters is looked uponvery favorably by the shellfish growers on the west coastof North America. Researchers at the University of Washington School of Fisheries have been instrumental in thedevelopment of the triploid oyster. The fact that these triploidoysters have minimal gametogenesis as compared withnormal diploid oysters and, thus, more carbohydrates in thetissues during summer, ensures that these neutered oysters
will be in great demand for the half-shell oyster trade during the summer months.

•

18°C
80

. . •.....•
'"

'

.

.....

0'
100

o

20°C

~ 80

P=.02 (T)290 e -L62lT
r 2 =.930

o

~

~ 60
~ 40
~

~

20

o """'<:>--'-_-L_-'-_-'------JL------L_-L_-'---'
100 r----,----,---.l.....-.II........,.----r----,.-----,.-----,.---,
250C ,._,

t80

I " ...

,"

60I

r 2 =.764
,

...

,
"

... '"~

20

P= .77(T )2.01 e-L069lT,... " ,

I

40

"

,
I

I

Oil-

I

' ..

II

ill

ril

Yl.

.....
jzI

_

~-

JZlI

--jzIIl_]X

Treatment periods

Figure 7
Induction profiles at 18°C (top), 20°C (middle), and 2SoC (bottom) were
produced by fitting curves to data using multiple linear regression.
Derived equations and correlation coefficients are shown. Points represent percent triploidy in each treatment group. Treatment periods are
IS-min intervals beginning at fertilization. (Downing and Allen 1987)

71

Citations_

Hershberger, W.K., J.A. Perdue, andJ.H. Beattie
1984 Genetic selection and systematic breeding in Pacific oyster
culture. Aquaculture 39:237-246.
Hochachka, P.W., and G.N. Somero
1973 Strategies of biochemical adaptation. W.B. Saunders Co.,
Phila., 358 p.
Jones, G., and B. Jones
1983 Methods for setting hatchery produced oyster larvae. Inf. rep.
4, Mar. Resourc. Br., Min. Environ., Provo Brit. Col., 94 p.
Koganezawa, A.
1975 Present status of studies on the mass mortality of cultural oysters
in Japan and its prevention. In Proc. Third U.S.lJapan Meeting on
Aquaculture, Tokyo, Oct. 1974, p. 29-34. Spec. publ., Jpn. Fish.
Agency and Jpn. Sea Reg. Fish. Res. Lab.
Krantz, G.E., G.J. Baptist, and P. W. Meritt
1982 Three innovative techniques that made Maryland oyster hatcherycost effective. Presented at the 74th Annu. Meet. Natl. Shellfish.
Assoc., Baltimore, MD, June 1982. MD Dep. Nat. Resourc., Annapolis 21401.
Lannan, J.E.
1980 Broodstock management of Crassostrea gigas: I. Genetic variation in survival in the larval rearing system. Aquaculture 21:
323-336.
Lannan, J.E., A. Robinson, and W.P. Breese1980 Broodstock management of Crassostrea gigas. II. Broodstock
conditioning to maximize larval survival. Aquaculture 21:337-345.
Lipovsky, V.P., and K.K. Chew
1972 Mortality of Pacific oyster (Crassostrea gigas): The influenceof temperature and enriched seawater on survival. Proc. Natl.
Shellfish. Assoc. 62:72-82.
Mann, R.
1979 Some biochemical and physiological aspects of growth andgametogenesis in Crassostrea gigas and Ostrea edulis grown at sustained elevated temperatures. J. Mar. BioI. Assoc. U.K. 58:95-110.
Matsumoto, B., M. Matsumoto, and M. Hibino
1934 Biochemical studies of Magaki (Ostrea gigas). II. The seasonalvariation in the chemical composition of Ostrea gigas Thunberg.
J. Sci. Hiroshima Univ. A4:47-56.
Muranaka, M.S., and J.E. Lannan
1984 Broodstock management of Crassostrea gigas: Environmental
influences on broodstock conditioning. Aquaculture 39:217-218.
Perdue, J.A., J.H. Beattie, and K.K. Chew
1981 Some relationships between gametogenic cycle and summer
mortality phenomenon in the Pacific oyster (Crassostrea gigas) in
Washington State. J. Shellfish. Res. 1:9-16.

Allen, S.K., Jr.
1986 Genetic manipulations. Critical review of methods and performances, shellfish. Paper presented at EIFAC/FAO Symposil:.m on
Selection, Hybridization and Genetic Engineering in Aquaculture of
Fish and Shellfish for Consumption and Stocking, Bordeaux, France,
May 27-30, 1987, 38 p. Rutgers Univ. Shellfish Res. Lab., Pt.
Norris, NJ 08349.
Allen, S.K., Jr., and S.L. Downing1986 Performance of triploid Pacific oysters. Crassostrea gigas(fhenberg). I. Survival, growth, glycogen content, and sexual maturation in yearlings. J. Exp. Mar. BioI. Ecol. 102:1-12.
Allen, S.K., Jr., S.L. Downing, and K.K. Chew
1989 Hatchery manual for producing triploid oysters. WSG 89-3,
Wash. Sea Grant, Univ. Wash .• Seattle, 27 p.
Beattie, J.B., W.K. Hershberger, K.K. Chew, C. Mahnken, E.F.
Prentice, and C. Jones
1978 Breeding for resistance to summertime mortality in the Pacificoyster (Crassostrea gigas). Wash. Sea Grant Prog. Rep. WSG 78-3,
13 p.
Beattie, J.H., K.K. Chew, and W.K. Hershberger
1980 Differential survival of selected strains of Pacific oysters(Crassostrea gigas) during summer mortality. Proc. Nat!. Shellfish.
Assoc. 70:184-189.
Beattie, J.H., J.A. Perdue, W.K. Hershberger, and K.K. Chew
1986 Effects of inbreeding and growth in the Pacific oyster during
summer mortality. Proc. Natl. Shellfish. Assoc. 70:184-189.
Breese, W.P., and R.E. Malouf
1975 Hatchery manual for Pacific oyster. Oreg. State Univ. Sea
Grant Prog. Rep. ORESU-H-75-D02, 23 p.
1977 Hatchery rearing techniques for the oyster Crassostrea rivularis.
Gould. Aquaculture 12: 123-126.
Buroker, N.E., W.K. Hershberger, and K. K. Chew
1975 Genetic variation in the Pacific oyster. Crassostrea gigas. J.
Fish Res. Board Can. 32:2471-2477.
Chaiton, J.A., and S.K. Allen
1985 Early detection of triploidy in the larvae of the Pacific oyster,
Crassostrea gigas, by flow cytometry. Aquaculture 48:35-43.
Chew, K.K.
1984 Recent advances in the cultivation of molluscs in the PacificUnited States and Canada. Aquaculture 39:69-81.
Clark, J.E., and R.D. Langmo
1979 Oyster seed hatcheries on the U.S. west coast: An overview.
Mar. Fish. Rev. 41(12):10-16.
Downing, D.L., and S.K. Allen, Jr.
1987 Optimum treatment parameters for induction of triploidy in
Pacific oyster, Crassostrea gigas, using cytochalasin B. Aquaculture
63: 1-21.
Gabbott, P.A.
1975 Storage cycles in marine bivalve molluscs: A hypothesis concerning the relationship between glycogen metabolism and gametogenesis. In Barnes, H. (ed.), Proc. 9th Eur. Mar. BioI. Symp., p.
198-211. Aberdeen Univ. Press.
Glude, J.B.
1975 A summary report of Pacific oyster mortality investigations
1965-1972. In Proc. Third U.S.lJapan Meeting on Aquaculture,
Tokyo, Oct. 1974, p. 1-28. Spec. publ., Jpn. Fish. Agency andJpn. Sea Reg. Fish Res. Lab.
Grischkowsky, R.S., and J. Liston
1974 Bacterial pathogenicity in laboratory-induced mortality of the
Pacific oyster (Crassostrea gigas, Thunberg). Proc. Nat!. Shellfish.
Assoc. 64:82-91.
Henderson, B.A.
1983 Handling and remote setting techniques for Pacific oyster larvae.
M.S. thesis, Oregon State Univ., Corvallis, 37 p.

72

A Physiological Approachto Problems of l\1ass
Culture of the Rotifer

Since the introduction of the rotifer Brachionus plicatilis tothe seedling culture as a food organism about 25 years ago(Ito 1960), mass-culture techniques for marine fish fry haveprogressed so remarkably that, for instance, two kinds offish can be produced in numbers exceeding 10 million peryear (1984) as seedlings for mariculture and for releasing
to the coastal waters (red sea bream, 39.3 million; flat fish,
13.7 million). Feeding schedules of seedlings were classified into four types according to size of larvae or type of
required foods (Fig. 1) (Kitajima 1985). The only fish seedlings that can be produced on a mass-production scale are
the standard type or the bottomfish type which can utilize
the rotifer as the major food throughout their larval stage.
This fact emphasizes the importance of the rotifer as a foodorganism.
Table 1 shows examples,of red sea bream, Pagrus major,
production in typical hatcheries in Japan. An average hatchery can produce more than 1 million young (> 10 mm total
length) per year. However, as shown in Table 1, comparedwith the tank volume needed for culturing fry, a much larger
tank volume is needed for rotifer production and an evenlarger volume for marine ChIorella culture. There have been
many attempts to develop artificial food for fry, and someof them are already being produced on a commercial scale.
However, these cannot completely replace the rotifer but only
function in a supplementary role. Therefore, the rotifer isand will remain the main food for fry production during thenext decade. Government officials project that the demandfor young red sea bream for release and mariculture willreach 50 million or more in 1987 (Aihara 1984). Twice thepresent rotifer production will be required for the releaseof artificially produced fish fry into coastal waters to effectively increase coastal resources and to supply enough fry
for mariculture.

KAZUTSUGU IDRAYAMA
Faculty of Fisheries
Nagasaki University
Bunkyomachi, Nagasaki, 852 Japan

ABSTRACTThe introduction of the rotifer Brachionus plicatilis as a foodorganism in 1960 has made such remarkable progress in the
mass-eulture techniques of marine fish fry that, for instance,
about 40 million red seabream young were produced in Japan
in 1984. Strains of rotifer used in Japanese hatcheries areroughly divided into two groups: L type and S type, according
to differences in morphology and in growth response to environmental temperature. The rotifer has high food selectivity.
Whereas living materials are usually acceptable, nonliving
materials are rejected by the rotifer, although there are many
exceptions. Greater attention to food selectivity is needed whenattempting to develop new kinds of food.
The dietary value of several kinds of phytoplankton were compared with marine Chlorella by conducting parallel tests underbacteria-free conditions. Green or blue-green algae were foundto be excellent food, while diatoms had a low dietary value. The
nutritive value of baker's yeast was found to be extremely low
when tested under bacteria-free conditions with pure washedyeast cells. Therefore, the success of mass culture of the rotifer
fed only yeast is due to byproducts of decomposition or to thegrowth of phytoplankton or bacteria in culture tanks whichbecome a supplementary source of the nutrient lacking in yeast,
such as vitamin B12 .
The rotifer requires fat-soluble vitamins A, D, and E as essential nutrients. The rotifer can tolerate relatively low oxygen level.
Low oxygen concentration is apparently suitable to rotifers fed
with yeast because the bacteria which produces vitamin B12 inculture tanks usually belongs to facultative anaerobic bacteria.
Un-ionized ammonia accumulating in culture tanks is probably one of the causes of suppressed growth of the rotifer. Also
pH may have an indirect rather than a direct effect on rotifer
growth through un-ionized ammonia.

Larval stage

Juvenile stage

Standard ty'"I§I

Eli W ,':-":'

type
Carnivorous

f=:;~~
n~~~~~~IT~-b==:::;:;:,_
UO§

fl7.mft5~====i~~~!=:b=====::::::::~
ElLJ
I!!!l

typel-J
Small fish

Larvae of bivalves.
Ultra tiny roWer '9

Rotiterp

J;S~SrooIl copepads']!\

L2J M~~~~I~ed foodFigure 1
Four types of feeding schedules for larval and juvenile stages of many
useful marine fishes.

73

I Hiroshima Prefectural Sea-Farming Center; II Hakatajima National Sea-Farming Center; ill Kamiura National Sea-Farming Center

Table 2
Characterhtics of two strains of rotifer.
LoricaLengthType

Water temperature (0C)

Shape(anterior spine)

Jim

Suitable

Lower limit
for growth

S (8. plicatilis rotundiformis)

150-220

Round(pointed)

28-35

20

L (B. plicatilis typicus)

200-360

Slender(obtuse angled)

18-25

10

This paper presents a physiological approach to present
problems in improving mass culture techniques of the rotifer.

Rotifer variations

as well as morphological variation in the electrophoretic
pattern (Serra and Miracle 1983, 1985; Snell and Carrillo
1984; Snell and Winkler 1984). Therefore, we should study
genetic differences between the two types by electrophoretic
procedures. These studies may add fundamental knowledge
to efforts to develop very small or very large strains by selection or hybridization, strains suitable for rearing small- or
large-mouthed fry.

_After introduction of the rotifer into mass production of fry ,early studies on the physiological responses of rotifers toenvironmental conditions ignored variations between strains.
However, recently the existence of great variations amongrotifers has become recognized. In Japan, strains of rotifers
used in hatcheries were roughly divided into two groupsL type and S type-according to size and shape of the lorica
and shape of the spines of the anterior lorica (Fukusho 1983).
The two strains also have different growth responses toenvironmental temperature. Table 2 summarized the morphological and physiological differences between Land S
types. S-type rotifers are suitable for rearing of smallmouthed larvae such as groupers and rabbit fishes. On theother hand, L-type rotifers are best for large-mouthed larvae.
Recent studies have shown that the Sand L types should be
divided into different genetic strains and classified taxonomically as subspecies B. plicatilis typicus and B. plicatilis
rotundiformis, respectively (Suzuki 1983). Studies outside
Japan reported the varieties in B. plicatilis that show genetic

Search for suitable food_

The food material usually used in rotifer mass culture ismarine Chlorella. However, recent investigations have revealed that some phytoplankton used as Chiorella in Japanese hatcheries belong to the family Eustigmatophyceae,
genus Nannochloropsis (Maruyama et al. 1986). As mentioned above, production of Chlorella requires a huge tankvolume and sometimes the supply is unstable. Therefore,
efforts have been undertaken to find suitable food material
to replace Chlorella. One approach is to culture the rotifer
with the objective food on a mass-culture scale. Tetraselmis
tetrathele has been introduced as a good suitable food algae(Okauchi and Fukusho 1984). Baker's yeast and marine yeast
have been practically utilized (Hirata and Mori 1967,

74

Table 3
Filter feeding of the rotifer Brachionus plicatilis.

Food
Dunaliella salina
Synechococcus sp.
Chlorella sp.
Chlamydomonas sp.
Olisthodiscus sp.
Protozoa
Bacteria
Dunaliella tertiolecta
Activated sludge

WatertemperatureDensity(cells/mL)(5.0-14.4) x 104
8x 106213 x 104lOx 104
5x 10<
1.75 x 105\.91 x 107\.03 x 104(0C)

Filtration rate
(IJI/h/ind.)20
26.1-28.1
25
23
23
25
25
?
25

0.64-1.5
3.0
4-6
8.4
2.0
8.1
3.4
10
0.33-5.45

Reference
Doohan 1973
Ito in Doohan 1973
Hirayama and Ogawa 1972
Chotiyaputta and Hirayama 1978
Chotiyaputta and Hirayama 1978
Hino et al. 1981aHino et al. 1981a
Deway in Starkweather and Gilbert 1977
Hino and Hirano 1980

Table 4Frequency (movement/min) of mastax movement of rotifers after feeding.
. _---

Seawater

Food

Chlamydomonas sp.
---------

Food

Avg.

SD

Baker's yeast
Pavlova lutheri
Cye/otella cryptica
Gluten

68.0
65.5
44.6
66.1

23.6
34.3
27.8
22.4

Egg albumin
Milk
Com starch
Olisthodiscus sp.
Linoleic acid
Oleic acid
Culture medium

70.1
66.1
78.1
58.8
79.6
79.6
70.1

30.2
22.4
2\.2
26.5
25.4
25.4
30.2

t test

*
*
**
***
***
***
***

Avg.

SD

t test

Avg.

SD

62.9
74.0
53.2
58.1

23.4
3\.2
27.7
15.7

***
***
***
***

22.1
33.3
I\.4
26.0

54.5
51.2
60.4
25.7
32.0
20.0
39.5

15.7
21.3
15.8
15.7
12.1
16.6
13.4

***
***
***

31.5
29.0
24.4

I\.6
20.0
10.5
16.3
17.5
16.3
17.1
11.2
16.7
16.7
17.5

**

20.6
34.4
34.4
31.5

*Significant at 5%; **significant at 1%; ***significant at 0.1 %.

food selection, as explained with B. cariciflores (Gilbert andStarkweather 1977). Therefore, after feeding various kinds
of food particles, the frequency of mastax movement may
reflect food selectivity. Table 4 presents frequencies of mastax movement after feeding many kinds of food particles,
together with frequency data of the same individuals fed thepreferred Chlamydomonas sp. and, as controls, only fIlteredseawater containing no food particles (Funamoto and Hirayama 1982). Differences between frequencies for each foodand for controls appear to be due to food selectivity. Manyliving materials are acceptable to the rotifer, while nonliving
materials are rejected, although there are many exceptions.
We must pay more attention to food selectivity as we attempt
to develop new kinds of food, because rejected food causes
severe problems by fouling the culture water, even if thenutritive value is complete for rotifer growth.

Furukawa and Hidaka 1973). Bacterial floes (Yasuda andTaga 1980), photosynthetic bacteria (Sakamoto andHirayama 1983), activated sludge (Hino et al. 1981a,b), dry
Ch10rella (Hirayama and Nakamura 1976), concentrated
CWorella, and AMT floes (Fukuhara et al. 1982, Higashihara
et al. 1983) have been examined. AMT is the residue of
distillation of alcohol produced by fermentation of molasses.
AMT floc means microbial floes produced from AMT plus
potassium phosphate with strong aeration. Formulated foodfor the rotifer is now under development (Gatesoupe andLuquet 1981; Gatesoupe and Robin 1981, 1982).
Another approach is to investigate the physiologicalresponse of the rotifer to food, such as food selectivity andnutritional requirements. Table 3 presents data on the filtering rates of rotifers obtained by using suspensions of manykinds of particles (Hirayama 1983). The broad distributionof data suggests that the rotifer is highly selective of food,though strains employed in the experiments may differ. Foodparticles that reach the mastax have passed three barriers for75

Culture methods
Relative

In order to evaluate the nutritive effects of foods or supplementary effects of nutrients added to the basic food suspension, batch culture and individual culture methods were
employed. When necessary, rotifers were cultured underbacteria-free conditions. The simplest is the batch culture
method in which offspring of the first-laid eggs hatched in
one day are cultured in test tubes, each containing four orfive individuals with the specific food to be tested. During
cultivation, the culture water is not replaced and no additional food is added to the tubes. After several days of culture,
the increase in the number of rotifers is determined and theeffect on population growth evaluated by comparing thechange in numbers of individuals.
In individual culture, first-laid eggs are cultured separately
in many test tubes, each containing two individuals under
defined conditions. These are observed daily with renewalof food suspension, and the numbers of surviving individuals
and of eggs laid are counted. From daily survival rate andfecundity data, two indices-net reproduction rate and intrinsic rate of population growth-are estimated by Birch's
method (Birch 1948). The values of indices calculated represent the growth phase of a group according to the fecundity
schedule obtained by the individual culture method. Net
reproduction rate (Ro) is the number of eggs laid by anaverage female in her lifetime or the rate of multiplicationin one generation. Intrinsic rate of population increase (r)is the constant in the differential equation of population increase, dN/dt = rN, in an unlimited environment (N =number of animals, t = days elapsed since beginning of test
tube culture).
The advantage of evaluation by batch culture is that theculture conducted through several generations makes theinfluence of physiological condition during stock culture
negligible. However, the batch culture has its disadvantage
in terms of the difficulty in keeping the density of food suspension constant.

Synechococcus
e!orgatus
Chlamydomonas
sp.
Pavlovalutheri
Dunaliellatertiolecta
Cyclotella
cryptica
Eutreptiellasp.
Nitzschia
c10striumTetr~~r6~lerrrrrrf-

r
05
I

0

1.0

A
A

A
A
A

l:>

A

..

A

L-

Relative0
Synechococcus
Chlamydomonas
Pavlova

-

Ro
10

0.5
I

••
••
f-.
•

•

r-

rr-

Dunaliella
Cyclotella
Eutreptiella0r-

Nitzschia

L-

Tetraselmis•

Figure 2
Relative values (closed symbols) of two indices for each phytoplankton
compared with dietary effect of marine Chlorella. Open symbols show
relative values for Cycrotello cryptica calculated against those of
Dunaliella terliolecta in a parallel experiment using the two species.

~ 280

2

'S

•

Yeast: 50,ug/ml

o Yeast: 200,ug/ml

u

III

240

~

"'Cl

r-

~

~

200
160

III

<ii
:>
:"S' 120

Nutritional comparisons

>

'6

.S

Several kinds of phytoplankton were compared with marine
ChIorella for nutritional value by the parallel test of individual
cultures under bacteria-free conditions, using the first-laid
eggs derived from an actively growing group (Hirayama
et al. 1979). The nutritional value of each plankton was
evaluated according to the ratios of rand Ro and comparedwith those obtained with Chlorella. The relative values ofmany phytoplankton shown in Figure 2 indicate that green
or blue-green algae are usually excellent food. Tetraselmis
tetrathele, which was recently recommended for use as a foodfor rotifer mass culture, possesses a higher nutritive value
for rotifer growth (Hirano and Hirayama 1984). The fact thatdiatoms have a low nutritive value agrees with the observation that the propagation of diatoms in mass-culture tanks
sometimes suppresses growth of the rotifers.

80

0
Q;
.0

E
:>

z

40

At inoculation
20 HIi---lL-----JL-----J----'----'----'---+
0
0.1
02
04
08
1.6
Concentration of vitamin B'2 ()Jg Iml)

Figure 3
Effect of supplementary vitamin B12 on rotifer numbers in suspensionof baker's yeast in batch culture, 23°C.

The nutritive value of baker's yeast was examined underbacteria-free conditions. Tests by both methods for nutritive
evaluation indicate a nutritive deficiency of the yeast (Fig. 3,
Table 5) (Hirayama and Funamoto 1983). The eggs laid are76although several kinds of food such as baker's yeast strengthened with essential fatty acid (w yeast) contain little vitamin
B 12 , the bodies of the rotifers grown successfully on suchdiets contained high levels of vitamin B I2 (Fig. 4) Imada
1984).
In Kaiike, Kagoshima prefecture, photosynthetic bacteria
growth supports feral rotifers as a main energy source (Matsuyama and Shirouzu 1978). After isolation of the bacteria,
the nutritive value of such bacteria to rotifer growth was examined. The photosynthetic bacteria could not support highgrowth of the rotifer, while an extremely low-level supplement of marine CWorella was effective in strengthening thenutritive value of this bacteria (Sakamoto and Hirayama
1983).
As mentioned above, improvement of the nutritive deficiency of baker's yeast by supplement of vitamin B12
indicates that vitamin B 12 is one of the essential nutritiveelements to the rotifer as shown by Scott (1981). Nutritive
requirements of the rotifer for fat-soluble vitamins were
examined by means of supplying each of them to the basic
food suspension of baker's yeast plus vitamin B12 • The
results by individual and batch cultures are shown in Figure
5. Each addition of vitamins A, D, and E was effective on
rotifer growth, and combinations of these vitamins are more
effective than addition of a single vitamin. These results indicate that the three vitamins are essential nutritive elements
for growth of the rotifer (Satuito and Hirayama 1986).

not viable, and the rotifers exhibited no growth. Additionof vitamin B 12 , however, can improve the nutritive value ofbaker's yeast so that, along with the supplement of vitamin
B 12 , it can support the growth of the rotifer. However, valuesof indices by two evaluation methods are still much lower
than those in marine Chlorella suspension. In spite of extremely low nutritive value of baker's yeast, there are manycases in which the successful mass culture of the rotifer wasachieved by feeding only baker's yeast as a food source. The
nutritive test on the decomposed marine yeast, and on the
addition of marine CWorella at extremely low density to amarine yeast suspension, revealed that the success of masscultures of rotifers fed with baker's yeast alone may be improved by the byproducts of decomposition or by the growthof phytoplankton or bacteria in the culture tanks (Hirayama
and Watanabe 1973). These provide a supplementary sourceof the nutrients lacking in yeast, such as vitamin B 12 • These
supplementary effects are also supported by the fact that,

Table 5
Two indices obtained by individual culture of rotifers in suspensionsof baker's yeast (50 Jlg/mL) supplemented with vitamin 8 12 invarious concentrations at 23°C.
Concentrationof vitamin 8 12Intrinsic rate of
population increase

Net reproduction
rate(Jlg/mL)

(r)

(Ro)

o

0.002
0.03
0.25

0.70
1.20
3.78

0.01
0.05

0.5
0.01

0.6
2.5

7.4

Environmental conditions regulating
rotifer growth

As mentioned above, the response of rotifer growth to temperature is different in Sand L strains (Table 2). L-type
rotifers tolerate relatively lower temperatures; in contrast,
S types are adjusted to relatively high temperatures (Ito et al.
1981). Although other physiological responses to environmental conditions may be reflected by strain differences,
there has been no study in which close attention was paid
to strain differences. On osmoregulation in the rotifer, it has
been shown that this species has a high ability to tolerate awide range of external concentrations of salts, and that thelack of ability to regulate hyposmotically at concentrations
approaching full-strength seawater suggests a marine ancestry
for this animal (Epp and Winston 1977). Observations in
mass-culture tanks showed that appropriate pH values formass culture of the rotifer ranged from 7.1 to 7.5 (marine
yeast) and 7.5 to 8.1 (baker's yeast) (Furukawa and Hidaka1973). However, Epp and Winston (1978) revealed by theirlaboratory culture that a wide range of pH, from 6.5 to 8.5,
had no direct harmful effect on the rotifer population growth.
Yu and Hirayama (1986) pointed out that un-ionized ammonia accumulating in the culture water could be one of thecauses of sudden decrease or suppressed growth of therotifer, and that high pH value may not directly, but may
indirectly, influence rotifer growth through un-ionized ammonia concentration.

6.6
5.3
11231
7258
42-89 13803
6222
1363E

I

_100

§9 0

•

I

10000
9000

(Jl

-:::8 08000 '"
u

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Figure 4Contents of vitamin 8 12 in culture water, (A) filtrates of AMT and
AMT floc, (8) in several kinds of food for the rotifer, and (C) in thebodies of rotifers produced by feeding that food (from Imada 1984).

77

AMT floc
4. 8X• yr ==29.5-0.72

30

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II tl.nocula t1.on

Figure 5
The supplementary effect of fat-soluble vitamins on the growth of therotifer. Vitamins were added to the basic food snspension consisting~f 200 I.Ig/mL of baker's yeast and 1.4 I.IglmL of vitamin B.2 • (A) Relative rand R. for each fat-soluble vitamin at different concentrationsin individual culture; (B) Total increase in population of the rotifer infood suspensions supplemented with fat-soluble vitamins at different
combinations in batch culture.

-1 00~~-~-----:~.....J.._~_J...

2

3
4
DO (mg/I )5GFigure 6
Relations between oxygen content and growth rate of two groups ofrotifer, one fed only AMT floc and one only w-yeast (from Imada 1984).

The rotifer can tolerate relatively low oxygen levels. Imada(1984) observed an inverse relationship between the oxygen
content of mass-culture tanks and the growth rate of rotifers
fed with AMT flocs or w yeast (baker's yeast strengthened
with essential fatty acid) (Fig. 6). This appears to indicatethat the rotifer grows better at low oxygen levels. However,this was not the case when marine Chlorella was provided
as a food. It seems likely that this relationship occurredbecause the bacteria which produced vitamin B 12 in yeastfed cultures are facultative anaerobic bacteria.
In mass culture of the rotifer there are many cases of sudden decrease or suppressed growth of the population. Someof these could be explained by physiological responses of
the rotifer as described above. However, we have many cases
which seem to have no relation to the causes mentioned

ab~ve: An abrupt change of water temperature may directly
or mdlrectly affect the growth of a rotifer culture. Suppressed
growth is often observed during a period of shift of dominant strains. Also, the fomation of large numbers of dormant eggs sometimes results in a sudden decrease of therotifer population. We often observe that suppressed growthis accompanied by an increase in diatoms or protozoa in thecultures.

78

Problems for future study

Higashihara, T.S., S. Fukuoka, T. Abe, I. Mizuhara, O. Imada, and
R. Hirano
1983 Culture of the rotifer Brachionus piicatilis using a microbial flocs
produced from fermentation syrups. Bull. lpn. Soc. Sci. Fish. 49:
1001-1013.
Hino, A., and R. Hirano
1980 Relationship between body size of the rotifer Brachionus plicatilis
and the maximum size of particles ingested. Bull. lpn. Soc. Sci.
Fish. 46: 1217-1222.
Hino, A., Y. Nogami, and R. Hirano
1981a Fundamental studies on the mass culture technics of the rotifer
Brachionus plicatilis making use of the secondary products of waste
water treatment-I. Rotifer culture providing with activated sludge.
Suisan Zoshoku 28:174-178 [in Jpn.].
1981b Fundamental studies on the mass culture technics of the rotifer
Brachionus plicatilis making use of the secondary products of waste
water treatment-II. Food-chain in the medium. Suisan Zoshoku
28:179-183 [in lpn.].
Hirano, K., and K. Hirayama
1984 The effect of Tetraselmis tetrathele as a food on population
growth of the rotifer Brachionus plicatiiis. Bull. Fac. Fish. Nagasaki
Univ. 56:21-23.
Hirata, H., and Y. Mori
1967 Mass culture of the rotifer fed baker's yeast. Saibai Gyogyo
5:36-40 [in lpn.].
Hirayama, K.
1983 The rotifer Brachionus plicatilis - Biology and mass culture(ed. Japan. Soc. Sci. Fish.). Suisangaku ser. 44:52-68. KoseishaKoseikaku Tokyo [in lpn.].
Hirayama, K., and K. Funamoto
1983 Supplementary effect of several nutrients on the nutritive deficiency of baker's yeast for population growth of the rotifer Brachionus plicatilis. Bull. Jpn. Soc. Sci. Fish. 49:505-510.
Hirayama, K., and K. Nakamura
1976 Fundamental studies on the physiology of rotifers in massculture-V. Dry Chlorella powder as a food for rotifers. Aquaculture
8:301-307.
Hirayama, K., and S. Ogawa
1972 Fundamental studies on physiology of rotifer for its massculture-I. Filter feeding of rotifer. Bull. lpn. Soc. Sci. Fish. 38:
1207-1214.
Hirayama, K., and K. Watanabe
1973 Fundamental studies on physiology of rotifer for its massculture-IV. Nutritional effect of yeast on population growth of
rotifer. Bull. lpn. Soc. Sci. Fish. 39: 1129-1133.
Hirayama, K., T. Takagi, and H. Kimura
1979 Nutritional effect of eight species of marine phytoplankton on
population growth of the rotifer, Brachionus plicatilis. Bull. Jpn.
Soc. Sci. Fish. 45:11-16.
Imada, O.
1984 Utilization of alcohol fermentation syrups as a possible resource.
Hakko To Kogyo 42:103-113 [in Jpn.].
Ito, S., H. Sakamoto, M. Hori, and K. Hirayama
1981 Morphological characteristics and suitable temperature for thegrowth of several strains of the rotifer, Brachionus plicatilis. Bull.
Fac. Fish. Nagasaki Univ. 51:9-16.
Ito, T.
1960 On the culture of maxoharine rotifer Brachionus plicatilis O.F.
Muller in the sea water. Rep. Fac. Fish. Prefect. Univ. Mie
3:708-740.
Kitajima, C.
1985 Fish nutrition and diets. Suisangaku ser. 54:75-88. KoseishaKoseikaku Tokyo [in lpn.].
Maruyama, I., T. Nakamura, T. Matsubayashi, Y. Ando, and T. Maeda
1986 Identification of the alga known as "marine Chlorella" as amember of Eustigmatophyceae. Jpn. J. Phycol. 4:319-325.

_

Many problems remain to be solved to establish more reliablerotifer culture techniques: 1) Select or produce the suitablesize of rotifer with a faster and more stable growth, 2)establish reliable mass-culture techniques of marine ChIorellaor find substitute phytoplankton, 3) clarify the nutritonalrequirements and to formulate completely artificial diets forthe rotifer, 4) completely clarify the environmental conditions regulating population growth, and 5) understand thefactors controlling bisexual reproduction.

Citations_

Aihara, M.
1984 Fundamental plan (Official plan on seed production and nursery
culture of marine useful animals). Official announcement details.
Saibai 32:41-50 [in Jpn.].
Birch,I.C.
1948 The intrinsic rate of natural increase of an insect population.
J. Anim. Ecol. 17:15-26.
Chotiyaputta, C., and K. Hirayama
1978 Food selectivity of the rotifer Brachionus plicatilis feeding on
phytoplankton. Mar. BioI. 45: 105-111.
Doohan, M.
1973 An energy budget for adult Brachionus plicatilis Muller(Rotatolia). Oecologia (Berl.) 13:351-362.
Epp, R.W., and P.W. Winston
1977 Osmotic regulation in the brackish-water rotifer Brachionus
plicatilis (Muller). J. Exp. BioI. 68:151-156.
1978 The effects of salinity and pH on the activity and oxygen consumption of Brachionus plicatilis (Rotatoria). Compo Biochem.
Physiol. 59A:9-12.
Fukuhara, 0., H. Yukawa, and T. Nishimura
1982 Culture of rotifer, Brachionus plicatilis (Muller), in an air lift
aquarium using alcohol fermentation sylups. Bull. Nansei Reg. Fish.
Res. Lab. 14:1-11.
Fukusho, K.
1983 Present status and problems in culture of the rotifer Brachionus
plicatilis for fry production of marin fishes in Japan. In Hector, R.
(ed.), Symposium International de Acuacultura Coquimbo, ChikeSeptiembre, Chile, p. 361-374.
Funamoto, K., and K. Hirayama
1982 Food selectivity of the rotifer Brachionus plicatilis expressedby using the frequency of mastax movement as an index. Suisan
Zoshoku 29:246-250 [in Jpn.].
Furukawa, I., and K. Hidaka
1973 Technical problems encountered in the mass culture of the rotifer
using marine yeast as food organisms. Bull. Plankton Soc. Jpn.
20:61-71.
Gatesoupe, F.J., and P. Luquet
1981 Practical diet for mass culture of the rotifer Brachionus plicatilis: Application to larval rearing of sea bass, Dicentrarchus labrax.
Aquaculture 22: 149-163.
Gatesoupe, F.J., and J.H. Robin
1981 Commercial single-cell proteins either as sole food source orin formulated diets for intensive and continuous production of rotifers(Brachionus plicatilis). Aquaculture 25:1-15.
1982 The dietary value for sea-bass larvae (Dicentrarchus labrax) of
the rotifer Brachionus plicatilis fed with or without a laboratorycultured algae. Aquaculture 27:121-127.
Gilbert, J.J., and P.L. Starkweather
1977 Feeding in the rotifer Brachionus calycijlorus-I. Regulatory
mechanisms. Oecologia (Berl.) 28:125-131.

79

Matsuyama, M., and E. Shirouzu
1978 Importance of photosynthetic sulfar bacteria, Chromatium sp.
as an organic matter producer in Lake Kaiike. lpn. l. Limnol.
39: 103-111.
Okauchi, M., and K. Fukusho
1984 Food value of a minute alga, Tetraselmis terrathele, for the rotifer
Brachionus plicatilis culture-I. Population growth with batch culture.
Bull. Natl. Res. Inst. Aquacult. 5: 13-18.
Sakamoto, H., and K. Hirayama
1983 Dietary Effect of Thiocapsa roseopersicina (Photosynthetic
Bacteria) on the rotifer Brachionus plicatilis. Bull. Fac. Fish. Nagasaki Univ. 54: 13-20.
Satuito, C.G., and K. Hirayama
1986 Fat soluble vitamin requirements of the rotifer Brachionus
plicatilis. In Maclean, l.L., et aI. (oos.) Proceedings, First Asian
Fisheries Forum, p. 619-622. Asian Fish. Soc., Manila, PhiliFpines.
Scott, J.M.
1981 The vitamin B 12 requirement of the marine rotifer Brachionus
plicatilis. l. Mar. BioI. Assoc. U.K. 61:983-994.
Serra, M., and M.R. Miracle
1983 Biometric analysis of Brachionus plicatilis ecotypes from Spanish
lagoon. Hydrobiologia 104:279-291.
1985 Enzyme polymorphism in Brachionus plicatilis populations fromseveral Spanish lagoons. Int. Ver. Theor. Agnew. Limnol. Verh.
Limnol. 22:2991-2996.
Snell, T.W., and K. Carrillo
1984 Body size variation among strains of the rotifer Brachionus
plicatilis. Aquaculture 37:359-367.
Snell, T.W., and B.C. Winkler
1984 Isozyme analysis of rotifer proteins. Biochem. Syst. Ecol.
12: 199-202.
Starkweather, P.L., and J.J. Gilbert
1977 Feeding in the rotifer Brachionus calycijlorus- II. Effect of fooddensity on feeding rates using Euglena gracilis and Rhodotorula
glutinus. Oecologia (Berl.) 28:125-131.
Suzuki, M.
1983 Taxonomical study on rotifers cultured for fry production.
Zool. Mag. (Tokyo) 91:657.
Yasuda, K., and N. Taga
1980 Culture of Brachionus plicatilis Miiller using bacteria as food.
Bull. lpn. Soc. Sci. Fish. 46:933-939.
Yu, J.P., and K. Hirayama
1986 The effect of un-ionized ammonia on the population growth of
the rotifer in mass culture. Bull. lpn. Soc. Sci. Fish. 52: 1509-·1513.

80Effects of Environmental
Instability on the Growthof the Japanese Scallop
Patinopecten yessoensis in
Abashiri Sowing-Culture
Grounds
NAOJI FUJITA

Along the Okhotsk Sea coast of Hokkaido in Japan (Fig. 1)
before 1973, production of the Japanese scallop Patinopecten
yessoensis depended on natural resources. Until 1945, theannual yield of scallop fluctuated markedly, but the highest
yield reached 15 thousand tons in Sarufutsu and othergrounds. However, yields decreased each year after 1945.
In 1973, sowing-culture began on a large scale in Sarufutsu.
This sowing-culture was a great success, reaching an annual
yield of 40 thousand tons in 1984. Subsequently, sowingculture has spread along the Okhotsk Sea coast.
In Abashiri Bay (Fig. 1) sowing-culture began in 1978.
In 1980, however, high mortalities and markedly slow
growth of sown scallops were observed. We have studied
the growth and survival of scallops in Abashiri sowingculture grounds from 1982 to 1984.

Faculty of Agriculture
Tohoku University
Amamiyamachi-Tsutsumidori
Sendai 980, Japan

Sowing-culture on the
Okhotsk Sea coast

KATSUYOSHI MORI_The Sea of Okhotsk is a semi-closed sea surrounded by land
and islands and has four distinct charactedstics. (1) The surface layer above 50 m depth, the Okhotsk Surface Water,
has very low salinity «32.5°/00). (2) Drift ice develops andcovers 80% of the Sea of Okhotsk in winter. (3) The Soya
Warm Water, of high temperature and high salinity, enters
into this sea through the Soya Straits (Fig. 1) from the Sea
of Japan. The Soya Warm Water flows along the coast of
Hokkaido and reaches the Siretoko Peninsula March to
October. (4) The continental shelves are as wide as 200 km
in the western part of this coast and become narrower to theeast, being only 16 km off Abashiri Bay.
Squares marked A, B, C, and D (Fig. 1) are rotating
sowing-culture grounds. Measurements of water quality andother elements were carried out at Station A in Abashiri Bay
and Station D off Lake Notoro (Fig. 1).
In these sowing-culture grounds, the removal of starfish
is carried out by dredging. After this, from 60 to 100 million
scallop juveniles, 1 year old, are sowed in June. After 2
years, the sown scallops are harvested.
In Abashiri A, sowing-culture began on an industrial scale
in 1978. However, it was found in 1980 that the survival
ratio was only 4.2 % and growth was slower than on the othergrounds of the Okhotsk Sea coast. Total wet weigl;1t of sownscallop at 3 years of age in Mutsu and Funka Bay, Okhotsk
Sea coast, and Abashiri A were 250, 170, and 80 g, respectively. Thus scallops in Abashiri Bay grew to only one-third
the weight of those in Mutsu and Funka Bay.
Scallops have been known to grow well in Abashiri D,
as in other grounds located in the western part of this coast;
however, they grow poorly in Abashiri Bay. Therefore, we

National Research Institute of Aquaculture
Fisheries Agency
Nansei, Mie 516-01, Japan

ABSTRACT
Environmental instability in Abashiri waters is caused by manyfactors, including geographical features, hydrographic structure, drift ice, and atmospheric conditions. Therefore, thedegree of instability varies year to year. The growth of scallops
is affected by environmental instability, especially by temperature fluctuations which depress feeding activities spring tosummer. Then, growth is slower than in the western part of
the Okhotsk Sea coast, and fluctuates according to the degreeof environmental instability each year. It is difficult to minimize such environmental effects on the growth of scallops.
However, the recatch:release ratios of sown scallops haveincreased year after year to 40%. This demonstrates thatreasonable methods can bring about an abundant harvest evenin inadequate environments such as Abashiri Bay.

81

40· t---v,.<t---------\d---------t-l

Figure 1
Location of the scallop grounds in the study area. Squares marked A, B, C, and D are rotating sowing-culture grounds.

Figure 2
Schema of hydrographic structure generally observed immediately after the disappearance of drift
ice from the Okhotsk Sea coast.

Environmental factors

expected to find distinct differences in environmental conditions between Stations A and D. However, the results ofmany water-quality measurements did not differ between
Stations A and D during 3 years. Therefore, we need toconsider other factors contributing to the inadequate environment for scallops in Abashiri Bay.

_

Winter drift ice
Drift ice causes extremely low water temperature, which
represses the growth of scallops. The duration of the drift
ice period varies markedly between years, from 2 to 5 months
in Abshiri, depending on climatic conditions.
82

Spring upwelling
After the disappearance of drift ice from this coast in Marchor April, the Okhotsk Surface Water spreads over the surface layer (Fig. 2). Along the western part of this coast, fromSoya Straits to near Lake Saroma, the Soya Warm Water(S.W.W.) occupies the entire water column and flows alongshore. Approaching Abashiri Bay, the S.W.W. sinks along
the deepening bottom, and then, off Abashiri Bay, theS.W.W. flows along the bottom at a depth of 100 or 200
meters. These hydrographic structures are caused by thehigher density of the S.W.W. and the deeper bottom around
Abashiri Bay. In any case, the S.W.W. rises to the surface
in summer. We can assume two processes which raise the
S.W.W. to the surface.
One of these processes is the decreased density in accordance with the rise in temperature of the S.W.W. With thisprocess only, it takes 2 or 3 months for the S.W.W. to reachthe surface layer. Therefore, temperatures in the coastal waterrise gradually, as shown in Figure 3, Station A, in 1982.
Another process is wind-induced upwelling. In this region,
upwelling induced by the east wind moves the surface water
offshore. Although the east wind is very small in this region,
the south wind also moves the surface water offshore.
In the spring of 1983, marked upwelling occurred withthe following processes. A strong south wind blew continuously for more than a week from the end of March to early
April and moved the drift ice offshore from Abashiri Bay.
At the same time, the surface water of the coast was transported offshore. Then the bottom water, the S.W.W., wastransported to the shoreline. Thus, the temperature rose
rapidly along the coast (Fig. 3). At the same time, the spring
phytoplankton bloom was removed and replaced by watercontaining low levels of nutrients (Fig. 4). Along this coast,-----------------i20
SIn. A. 30m.~.j0-",/.I ····.i\-----------------cr-:------+-i15........ 1982
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-1984

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Figure 3
Seasonal temperature variations at 30-m depth at Abashiri Stations A(upper) and D (lower), 1982-84.

SIn. A

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1982
1983
1984
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83

Seasonal variations in cumulative (0-30 m) chlorophyll a at Abashiri Station A, 1982-84.

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Figure 5
Daily mean temperature variations (dotted line) at 28-m depth of Abashiri Station
D measured with Ryan Model J, and daily mean wind speed (solid line) observedby Abashiri Regional Meteorological Observatory, April-September 1984.

a phytoplankton bloom is expected to develop once a year,
although the scale of the spring bloom fluctuates widely. The
largest amoung of chlorophyll a was 270 mg/m 2 in 1984,
and the smallest was 60 mg/m2 in 1983 (Fig. 4).
The scallop spawning season is May to June in this area.
Spring phytoplankton bloom is thought to be the major foodsource for scallops just prior to spawning. These fluctuationsof spring bloom are considered to be a disadvantage for the
spawning of the scallops.
The same phenomena were observed in the next year,
1984. From April to June, three temperature peaks wereobserved (Fig. 5), caused by upwelling of the S.W.W. induced by strong south winds. Thus, the S.W.W. was brought
up to the upper layer. At the period indicated by the arrow
in Figure 5, the S.W.W. reached the surface. After thisperiod, the upper layer of the water mass was replaced by
the lower, and this upwelling caused the sudden fall intemperature.

off Abashiri Bay, the S. W.W. occupies the upper layer fromthe surface to about a 100-meters depth (Fig. 6). The temperature gradients extend horizontally. The area between thebottom of the S.W.W. and the sea bottom is occupied bycold water. Under this structure, upwelling causes a sudden
temperature drop and many other mechanisms cause temperature fluctuations on this coast.
In August of 1984, rapid temperature changes wereobserved most frequently (Fig. 7). Daily cyclic changes
ranging from 3 to 5°C were observed in early August,probably caused by internal tides under the two-layered structure shown in Figure 6. The rapid fall in temperature of 13 °C
during 20-25 August was caused by upwelling induced bya strong south wind. These rapid temperature changes are
the main factors that cause environmental instability.
It is clear that daily temperature ranges are wide from May
to mid-September. Then, after mid-September, the daily
range becomes narrow (Fig. 5) because the layering structure of the water masses is destroyed by the cooling of thesurface water.

Summer temperature fluctuation
After reaching the surface, the S.W.W. flows alongshore,
occupying the entire water column off Lake Notoro, andtemperature gradients extend vertically (Fig. 6). The samestructures are observed generally in the western part of thiscoast. It is believed that this hydrographic structure prevents
upwelling and temperature fluctuations. On the other hand,Intermediate cold water in summer
Finally, environmental instability along this coast is due tothe approach of the Intermediate Cold Water (LC.W.) to thecoast. This LC.W. is of very low temperature, from -1.8
to +2°C, and exists below the 50-m depth even in summer.
84

..

.

. . . . . . . . . . •• • •0'Figure 6
Schema of hydrographic structure generally observed in summer along the Okhotsk
Sea coast. S.W.W. = Soya Warm Water; I.C.W. = Intermediate Cold Water; boldlines = temperature gradients.

20

~

r~

..If

5

~
I

tJ,rJ '\ V

~

V

I~

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\~
5

5

10

15
August20

25

31

Figure 7
Two-hour temperature variations at 28-m depth of Abashiri Station A measured
with Ryan Model J, August 1984.

Figure 8 shows the hydrographic structure during September of 1984. Off Lake Notoro, the front of the LC.W.
is usually located 25-40 miles offshore (Ohtsuki 1983).
However, it was only 9 miles offshore in 1984, the closest
approach to shore in 18 years. Then, the S.W.W. condition
became unusual, that is, the temperature gradients extended
horizontally off Lake Notoro as off Abashiri Bay. Thishydrographic structure easily caused the temperature fluctuation nearshore. On this coast, temperatures generally do
not fluctuate; however, it seems that temperature fluctuations should occur once every 10 or 20 years by the approachof LC.W. to this shore.

85

Figure 8
Schema of unusual hydrographic structure observed in September 1984 along the
Okhotsk Sea coast. S.W.W. = Soya Warm Water; I.C.W. = Intermediate Cold
Water; bold lines = temperature gradients.

In situ biodeposition
rates and growth_

In order to understand the relationships between environmental conditions and feeding activities, in situ biodeposition rates
of scallops were measured. The term "biodeposits" coined
by Haven and Morales-Alamo (1966) means "feces andpseudofeces" which are produced by filter-feeding animals,
such as scallops, and deposited on the bottom.
In situ biodeposits were collected with sampling apparatus
designed by us (Fig. 9). Two-year-old scallops were fresWy
caught from the bottom of each station. One apparatus withfour scallops and one control apparatus without scallops wereplaced on the bottom. After one day, biodeposits were collected and dry weight measured.
It was expected that biodeposition rates would increase withincreases in the amount of food. However, the results did
not show such relations (Fig. 10). It is concluded that theextremely low biodeposition rates obtained in ice-covered
Lake Notoro in winter (open circles, Fig. 10) resulted fromdepressed feeding activities caused by the extremely low
temperature (-1.6°C). We consider that biodeposition rates
below 200 mg/individual per day are also depressed by environmental factors perhaps related to the rapid and frequentchanges in temperature in Abashiri waters.
In consideration of some studies on thermal adaptation(Somoero 1969, Dickie and Medcof 1963), we have assumed
that aquatic poikilotherms, such as scallops, that live on the

i
E
u

o

<D

1

Figure 9
Sampling apparatus used for collection of
biodeposits of Japanese scallops.

86SIn. A••

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o

•

o

Chi a 061()JgIlJ••°O!,-----;:;-'-;::--~:__-...,..L,----L.0.5
1.0
1.5
2.0
Chlorophyll a ()Jg/lJ

116

0.96

0.19

5 '--~~~.L;;-;-'-;;:;:-"L::;;;-''-;;;;-...l...----,-::-:,JJ...,,..,.--'-~L---'-.,----,----loJuly
23 24 25 26 27
23 24 25 26 27

Date

Figure 11
Figure 10
Biodeposition rates of 2-year-old scallops in relation tochlorophyll a of ambient water in Abashiri Bay (.) andice-eovered Lake Notoro (0), 1982-84.

Biodeposition rates of 2-year-old scallops (vertical columns) at Abashiri Stations A Oeft)and D (right). Scallops used were captured at Station A. Temperatures were measured
with Ryan Model J (solid line) and with water sampled (dashed line). Horizontal lines
show sampling periods of biodeposits. Amounts of chlorophyll a were obtained at thebottom of Stations A and D on 23 and 27 July 1984.

Seasonal variation of biodeposition rates

sea bottom cannot adapt quickly to rapid changes of temperature. We examined this assumption by in situ measurements. The biodeposition rates obtained at Station A withscallops caught freshly at the same place were 180 mg/day
on 23-24 July, and decreased to 138 mg/day with an increasei~ temperature of 3 ° C during three successive days (left,
Fig. 11).
The right graph in Figure 11 shows the measurements at
Station D with scallops caught at Station A. During the period
23-24 July, scallops were exposed to a sudden rise and fallin .t~mperature over the range of about 5°C and the biodepOSitIOn rate was reduced to 40 mg/day. This is only 20%of that of Station A and as low as that caused by the extremely
low temperatures. During three successive days, the biodeposition rate increased a little, but under these fluctuating
temperature conditions, it was only half that of Station A.
From the results above and knowledge of the effects ofthermal changes, we believe that feeding activities are frequently depressed by fluctuating temperatures from spring
to summer in Abashiri Bay.

Seasonal variations in amount of biodeposits are calculatedwith biodeposition rates obtained in Abashiri waters (Fig.
12). The numbers in every column in Figure 12 indicate theamount of biodeposits produced during every period. From
September to December, temperature fluctuations are not somarked, as mentioned previously, and the scallops feed constantly in the stable environment. However, even theseamounts of biodeposits are not large, because of the small
amounts of food available during this season. In Mutsu Bay
where the scallops grow faster than in Abashiri

0>-;;;~ 600~>oIII.~~ 400_.-:.
.- '0
CIl

c

&::::: 200-

32.6 9

4/0\

'OE
o~

([j

0

S

OlN1D

6.9 9
J

I

F I M I A

9.5 9 110.4 9
M I J I J I A

IFigure 12
Seasonal variations in amounts of biodeposits of a 2-year-old scallop
in Abashiri Bay, 1982-84.

87

Bay, the biodeposition rates were almost identical with thatof Abashiri Bay in this season (Fuji and Hashizume 1974).
In winter (January-April), the extremely low temperature
over a fairly long period depresses feeding activities in
Abashiri waters. In Mutsu Bay, the most active feeding isdone in this season, and the amount of biodeposits reach
80.9 g (Fuji and Hashizume 1974). This active feeding in
Mutsu Bay is supported by the spring phytoplankton bloom
and by higher temperatures (4-8°C) than Abashiri waters.
From spring to summer in Abashiri waters, the amount of
biodeposits increases slightly, but it is still small, caused bytemperature fluctuations as mentioned previously. Thus, theannual amounts of biodeposits produced by a 2-year-old
scallop in Abashiri and Mutsu Bay are 59.4 and 151 g (Fujiand Hashizume 1974), respectively. The Abashiri:Mutsu
ratio is 0.39, being similar to the ratio of total weight.
Therefore, we conclude that the causes of slow scallop
growth in Abashiri Bay are the extremely low temperature
in winter and temperature fluctuations from spring to summer. The magnitude of this fluctuation should vary every
year. In the western part of the Okhotsk Sea coast, including Abashiri D, the winter temperature is low, but temperatures from spring to summer are stable at which time thescallops grow well.

180

o

0
......

o160
oo .. ··0

140
~120

~

.;

.,,'

.. ,

.d

°

o

o

o

0, 1983oB,1982•.

It- - - 11: _l5.

x

• •

•

-x_ ~ - I{" - - - - Jr -.r -II

C,19844020O'--;-:-::----l...--;-;-_...l..-:-----..l.---;---;----L--:-_...l..-=__~

Apr.

May

Jun.

Jul.

Aug.

Sep.

Figure 13
Growth of 2- to 3-year-old scallops at Abasbiri Stations B (. 1982),
D (0 1983), and C (x 1984), April to September.

200

40

Spring-summer scallop growth
Figure 13 shows total wet weight of scallops from April to
September for 3 years. The weight is the average of 30 to2000 scallops obtained by harvesting operations in each year.
They show various growth rates in this season, such as rapid
increase in weight from April to May (Abashiri B 1982,
Abashiri D 1983) and decrease in weight from May to Junecaused by spawning. However, it is clear that in Abashiri
B 1982 and Abashiri C 1984 the scallops grew very slowly
from July to September. This slow growth is probably causedby the rapid temperature fluctuation as mentioned above.

0

/\
/ \

150

/

0

01

j\

:c

/

01

j

'Qj

~ 100

Q;

j

~

/

/

\
\

30~

\
\

0

~
0

':...G

/
\

/

/

Q>
<II

0

/

20~
~

.c.

"'

u

<5

':uG

I-

Conclusions

_

Q>

50

Overall results of sowing-culture from 1978 to 1985 areshown in Figure 14. The highest weight was 170 g in 1983
at Abashiri D. In the other grounds of Abashiri Bay, Abashiri A, B, and C, the weight fluctuated between 140 and
60 g. It is clear that there is no trend toward increase or
decrease in weight. We conclude that these fluctuating growth
rates reflect the environmental instability in Abashiri waters.
On the other hand, the recatch:release ratio increased year
after year to about 40 % in 1985. This indicates that there
is no relationship between growth and survival. The decreaseof predation by starfish may explain the trend of increasein the survival ratio through the years. It is well known thatstarfish are the main predator of scallops. In these sowingculture grounds, the removal of starfish has been carried out
successively since 1978. It is believed that the numbers of
starfish have gradually decreased and the survival ratios

10

a:

A
c
B
o
B
Ol~=____;;!;::--~~-:-:l:-:------.Jl.--.L-.JO

c

1980

1981

1985

Figure 14
Yearly variations of total wet weight of 3-year-old scallops in September (0) and release:recatch ratio (.) in the Abashiri scallop grounds(A-D), 1980-85.

88

have increased year after year. Actually, a marked decreasein numbers of swfish from 0.39/m2 (June 1980) to 0.07/m2(July 1985) was observed in Abashiri A.
In the present study, we determined that environmental
instability was especially marked in Abashiri Bay, causing
slow and fluctuating growth. However, continuous efforts
to eliminate predators such as starfish and to collect large,
healthy seed scallops and release them at both a suitable timeand a rational population density have brought about an abundant harvest even in Abashiri Bay, though the weight ofindividual scallops is small.

Acknowledgments_

We wish to express our appreciation to Kazuhiko Konishi,
Faculty of Science, Tadashi Nomura, and Satoshi Nishizawa,
Faculty of Agriculture of Tohoku University, for their advice in planning research. Our thanks also to the membersof Abashiri Fisheries Cooperative Association, Hokkaido,
who assisted our study.

Citations_

Dickie, L.M., and J.e. Medcof
1963 Causes of mass mortalities of scallops (Placopecten magellanicus)
in the southwestern GulfofSt. Lawrence. J. Fish. Res. Board Can.
20:451-482.
Fuji, A., and M. Hashizume1974 Energy budget of a Japanese common scallop, Patinopecten yessoensis (Jay), in Mutsu Bay. Bull. Fac. Fish. Hokkaido Univ.
25:7-19.
Haven, D.S., and R. Morales-Alamo
1966 Aspect of biodeposition by oysters and other invertebrate filter
feeders. Limnol. Oceanogr. 1l:487-498.
Ohtsuki, T.
1983 Variations of "Intermediate Cold Water-front" in summer,
southwestern Okhotsk Sea. J. Hokkaido Fish. Exp. Sin. 40:211-226.
Somoero, G.N.
1969 Enzymic mechanisms of temperature compensations: immediate
and evolutionary effects of temperature on enzymes of aquatic poikilotherms. Am. Nat. 103:517-530.

89

Mantis Shrimp:
Its Fishery andBiological Production

The mantis shrimp, Oratosquilla oratoria (de Haan), is a
stomatopoda crustacean inhabiting the sandy mud bottom inthe coastal waters of temperate and subtropical regions of
the northwest Pacific Ocean. In Japan, this shrimp has beencaught in large quantities C''-'5000 tons per year) in the coastal
waters of Tokyo Bay, Ise Bay, and Seta Island Sea, and used
for food in "Sushi. " The fishery in Tokyo Bay (the processfrom fishing to forwarding) is described in this paper as one
example of the fishery for this shrimp. Also the process of
biological production of adult mantis shrimp is described,
which is important as the basis of the explanation of population dynamics of this shrimp.

MAKOfO YAMAZAKI
Seikai National Fisheries Research InstituteKokubu-rnachi. Nagasaki 850. Japan

Fishery in Tokyo Bay_

The mantis shrimp is one of the most important fishing targets
in Tokyo Bay. The shrimp fishery is conducted with the aidof a Danish seine boat (Fig. 1) carrying a type of hand trawl.
After trawling for about one hour, the net is hauled (Fig.
2) and the mantis shrimps are selected from the catch on deck
(Fig. 3). Shrimps are transported live in holding tanks andare boiled soon after landing (Fig. 4). The carapace (cephalothorax) and both sides of the abdominal exoskeleton are
cut with scissors (Fig. 5) and the shells are removed by hand(Fig. 6). The shucked shrimp, graded by size, are packed
in plastic cases (Fig. 7) and forwarded (Fig. 8).
The fishermen engaged in the Tokyo Bay fishery haverestricted themselves to the ratio of 2: 1 days (i.e., 4 days
operation per week) to ensure the shrimps' stable production and to preserve its price in the market by controllingthe volume produced. Compared with other production areas,that of Tokyo Bay is relatively stable.

Process of biological production_

In contrast to the Tokyo Bay fishery, the annual catch ofmantis shrimp fluctuates widely among the prefectures. To
maintain the catch at a certain level, two problems must be
resolved: One is to develop techniques of resource management, and the other is to intensify efforts for artificial recruitment to the shrimp population. To resolve these problems,
systematic ecological investigations of the natural populations and of the primary factors affecting population dynamics
are needed. Until now, however, these kinds of studies havebeen rare.
A series of investigations was undertaken by the author
to determine the biological production of adult mantis shrimp,
based on the ecological aspects of reproduction, growth, andfood consumption, and to clarify the distribution of energy
from food intake to the growth of reproductive organs andother body parts. All shrimp used in this research were obtained from Mutsu Bay, Aomori Prefecture of northern
Japan.
91

Figure 1
Danish seine
boat carrying
a type of hand
trawl.

Figure 2
Net hauled
after about
one hourtrawling.

Figure 3
Man& shrimps
selected fromthe catch on
deck.

Figure 4
Man& shrimps
boiled soonafter landing.

Figure 5
Cutting bothsides of theabdominal
exoskeleton
with scissors.

Figure 6
Shucking theshells by hand.

Figure 7
Shuckedshrimps packed
in plastic cases.

Figure 8
Shrimps prior
to forwarding.

92

--

Figure 9
Scheme of the reproductive cycles of the mantis shrimp. [lJ Recovering, [Q] developing~ prematuring, [!] maturing,
spawning (female) and sperm-ejecting (male)period.

D

Reproductive cycle(Table I). From these results, adult growth in length appeared
stepwise (Fig. 11). From three groups of pre- and postmoulting body length presented in Figure 11, the following
equation is derived by means of the graphic method of Hiatt(1948).

The reproductive cycle of mantis shrimp was described by
Yamazaki and Fuji (1980), summaried as follows.
The developmental processes of germ cells in both sexes
were arbitrarily categorized into stages by histological techniques. On the basis of these stages of the development ofgerm cells, the maturation processes were classified into fourstages in the ovary and five stages in the testis. The valueof the gonad index, which is the ratio of the wet weight ofgonadal tissues to the total body weight, is correlated withthe gametogenetic development in both sexes.
The annual reproductive cycle in the female population ofmantis shrimp was broadly classified into the following five
periods, according to the course of seasonal variation of the
gonad index and the duration of active appearance of eachgonadal stage: 1) Recovering (Aug-Sept), 2) developing(Oct-Nov), 3) prematuring (Dec-Feb), 4) maturing (MarMay), and 5) spawning (June-July). In similar procedures,the cyclical reproductive processes in the male population~ere divided as follows: I) Recovering (July), 2) developmg (Aug-Sept), 3) prematuring (Oct-Dec), 4) maturing(Jan-Apr), and 5) sperm-ejecting (May-June) (Fig. 9).

Ln +\ = 0.755Ln + 4.743(1)

where L n and L n +\ are the linear dimensions of pre- andpostmoulting, respectively.
The value of 0.755 shows that its growth pattern is of theretrogressive geometric type (Kurata 1960), and that theamount of increase at successive moultings decreases in proportion to the increase in initial premoulting body length.
Changes in body weight and body component weight(integument, muscle, hepatopancreas and gonad) Lengthweight regression equations were obtained monthly from therearing experiment, and the slopes of these equations were
unified to a value by statistical analysis (Table 2). From theseequations and the body length derived from the equation (1),the.seasonal body-weight change was derived (Fig. 12). Body
weIght (and body length) increases by a large increment after
moulting, and there is a remarkable variation resulting frommaturation and spawning in the female.
The regression equations of body weight-dry component
weight were obtained from bimonthly dissections. Based onthese equations, the seasonal changes in dry weight of bodycomponents were derived from any body length without
dis~ections (Table 3). The striking seasonal variations of dry
weIght of body components reflect the accumulation and con~u~ption of substances concerned with spawning and moultmg m females. However, in males there are no large changes
throughout the year except the increment at moulting.

Growth pattern
Change in body length Mantis shrimps were sampledmonthly by bottom gill net (7.6 cm mesh) April 1976September 1977 and May 1981-December 1982. Frompolymodal length-frequency distributions, several fitted
normal curves were analyzed by the probability graph paper
method of Harding (1949) (Fig. 10). And from these normal curves, the seasonal fluctuation in mean body length ofeach cohort was obtained. The rearing experiment for theobservation of moulting was made September 1981-December 1982, and moulting was observed only August-October
93

]M'Y~,

II

1:1J~M

I:l°~j~"~'rCI29~oJ-------,-------""
M.d"S2

"

!\~

~~

J

I

Iro"s

~
I

I~::!L

ol~~-

~'~

J~nnn

n

\

i

Sep20

\

\

\

IO.~
O~l

n

\

10jOCl17\\~-e-II~

01

I

~

1:J

16

~

1010.C6

Figure 10

oJ~o-----='1!:""':..L...--~,6,.---.::=....o::n""",919

Histograms showing frequencies of body length andseveral fitted nonnal curves calculated by the probability graph-paper method. Broken lines indicate
the flow of mean body length of each cohort.

length (em)Body

Table 1
Number of moulting individuals among mantis shrimps reared
September 1981-December 1982.
Month
S 0

,,

I
I
I

.• ......• ..'-" . ·_-:--------n-'.
.·.··.:.,. . -...
•

Group III

I

1
I

1

8

"
....'"co
z

~
><
0

t·'

,

,

Female 2 11 0
Male
3 13 0Total
5 24 0, >-------+-I

I

I
I

Group II

l>

6°
l>

A'I

I

I

I

I
I

:. ;

l>

l>
l>

I

I
I

,

I

M

A

A

M
MONTH

6 5 0
8 7 0
14 12 0Figure 11

I

postI
pre-maulting
r moulting
moulting
per~od~'" periOd~ period

F

0 0 3
0 0 3
0 0 6

l>

I

I
I
I

0
0
0

~-

I

12

0
0
0

N D

4

l

I

0
0
0

0

l> I

•

e : ....

Group I

0 0 0
0 0 0
0 0 0

S

I
I

•

,

I

14

0

'"

~.

N D J F M A M J J A

SON

I

D

Seasonal variation in modal length of the shrimp body for each sizegroup. Each mark indicates the mean body length of each cohort shownin Figure 10. Straight lines indicate the mean values of marks withineach size-group. In Group I, mean values are 12.2 cm (pre-moulting)and 13.8 cm (post-moulting); in Group II, 14.0 cm and 15.6 cm; andin Group ill, 15.9 cm and 16.6 cm, respectively.

94

0
0
0

Table 2

Moul ting

Values of constant (a) in length-weight regression
equation, W = aL3 •06ll , of the mantis shrimps
reared.

I

60

--..

FemaleMale

2 Nov
16 Dec
5 Jan
2 Mar
6 May
9 June10 July
17 Aug6 Sept
5 Oct
4 Nov
4 Dec

-1.935-1.946-1.940-1.942-1.934-1.915-1.955-1.951-1.935-1.956-1.947-1.964-1.925-1.938-1.923-1.917-1.924-1.933-1.938-1.929-1.944-1.943-1.944-1.954..

,~"jGroup I I I

Dater·:_'':::.~

Spawning--.~~::~::::.--.--.

·1--.---"'>~ .0.---.-'

6------.o__Group I I

-c
c

~

.

,'.-- ~./~/"_/"'-"--:::=:--c::::.,_._.--_._
"i.
>-

•

;,

i'

)

.>t~._-.-.:o--.~
.

-e--e

I

~a/

.... -

V

co

'":

j

Group I=.::::e.-.--,.....e::::::~
tf~.-·>Io---e--·

20

I

o

A

J

A

o

o

M0 nthFigure 12
Seasonal change in body weight calculated by substituting the lengthweight regression models shown in Table 2 for the body length derived
from the equation L.+ 1 = O.755L. + 4.743, starting with 12.2 em.
Circles indicate female weight and triangles indicate male. Values atspawning and moulting are shown at 15 June and 15 September with
open marks.

Table 5
Changes in energy values of muscle, hepatopancreas, integument, exuviae, gonad, and spawn of mantis shrimp. See Table 3.
Energy value (kcal)

Size
group

II

ill

Date

Body
length(cm)

12 Dec9 Feb
II Apr
9 June15 June
10 Aug6 Sept15 Sept
13 Oct22 Dec12.2

12 Dec9 Feb
II Apr
9 June15 June
10 Aug6 Sept15 Sept
13 Oct22 Dec14.0

12 Dec9 Feb
II Apr
9 June15 June
10 Aug6 Sept15 Sept
13 Oct22 Dec

15.3

14.0

15.3

16.3

Body weight
(g)

Male

FemaleFemaleMale

MuscleHepat.

Integ.

Exu.

Gonad

Spawn

MuscleHepat.

Integ.

Exu.

24.4
24.7
24.9
26.2
23.6
24.1
25.0
34.4
36.5
36.8

24.9
25.9
25.8
25.1

8.77
8.86
8.95
9.48
8.42
8.64
8.99
12.80
13.69
13.78

1.50
1.06
1.39
0.95
0.83
0.67
1.17
1.83
1.28
2.67

4.52
4.58
4.61
4.82
4.38
4.47
4.63
2.59
6.59
6.63

0.00
0.00
0.00
0.00
0.00
0.00
0.00
3.02
0.00
0.00

0.94
0.52
0.78
4.55
0.26
0.37
0.21
0.37
0.26
2.04

0.00
0.00
0.00
0.00
6.17
0.00
0.00
0.00
0.00
0.00

8.95
9.35
9.30
9.04

l.ll
1.22
1.17
1.17

5.15
5.33
5.31
5.18

0.00
0.00
0.00
0.00

9.08
8.82
14.04
14.04
14.31

1.17
1.11
2.00
2.00
2.06

5.20
5.07
2.79
7.51
7.63

0.00
0.00
3.26
0.00
0.00

14.00
14.13
14.26
15.II
13.47
13.78
14.35
17.28
18.52
18.65

2.72
1.89
2.50
1.78
1.50
1.22
2.17
2.72
1.89
3.95

6.72
6.76
6.81
7.16
6.50
6.62
6.85
3.33
8.49
8.54

0.00
0.00
0.00
0.00
0.00
0.00
0.00
3.93
0.00
0.00

2.09
1.20
1.67
10.04
0.58
0.84
0.47
0.63
0.42
3.40

0.00
0.00
0.00
0.00
9.54
0.00
0.00
0.00
0.00
0.00

14.31
14.93
14.84
14.44

2.06
2.17
2.17
2.06

7.63
7.91
7.87
7.69

0.00
0.00
0.00
0.00

14.53
14.04
18.96
19.00
19.31

2.II
2.00
2.95
2.95
3.00

7.74
7.51
3.59
9.68
9.83

0.00
0.00
4.27
0.00
0.00

18.92
19.09
19.27
20.42
18.21
18.61
19.40
21.44
22.90
23.12

4.00
2.78
3.73
2.56
2.22
1.83
3.17
3.61
2.45
5.23

8.64
8.70
8.79
9.21
8.38
8.52
8.83
3.99
10.17
10.25

0.00
0.00
0.00
0.00
0.00
0.00
0.00
4.76
0.00
0.00

3.45
1.99
2.82
16.68
0.94
1.41
0.78
0.52
0.58
4.86

0.00
0.00
0.00
0.00
12.68
0.00
0.00
0.00
0.00
0.00

19.27
20.20
20.07
19.49

3.00
3.17
3.17
3.06

9.81
10.20
10.15
9.91

0.00
0.00
0.00
0.00

19.62
18.96
23.52
23.57
23.97

3.06
2.95
3.89
3.89
3.95

9.96
9.67
4.32
11.62
11.78

0.00
0.00
5.18
0.00
0.00

37.3
37.6
37.9
39.9
36.1
36.7
38.1
45.1
48.0
48.3
48.9
49.3
49.8
52.4
47.3
48.2
50.1
54.8
58.2
58.7

25.2
24.5
37.4
37.4
38.0
38.0
39.5
39.3
38.3
38.6
37.4
49.0
49.1
49.9
49.8
51.9
51.6
50.3
50.6
49.0
59.6
59.7
60.6

Table 6
Amount of absolute growth derived from Table 5, expressed in kilocalories.

Size
group

Duration ofrearing(days)

MuscleHepat.

Integ.

Exu.

Gonad

Spawn

MuscleHepat.

Integ.

Exu.

FemaleMale

59 (Dec-Feb)
61 (Feb-Apr)
59 (Apr-June)
6 (June-June)
56 (June-Aug)
27 (Aug-Sept)
9 (Sept-Sept)
28 (Sept-Oct)
70 (Oct-Dec)

0.09
0.09
0.53
-1.06
0.22
0.35
3.81
0.89
0.09

-0.44
0.33
-0.44
-0.12
-0.16
0.50
0.66
-0.55
1.39

0.06
0.03
0.21
-0.44
0.09
0.16
-2.04
4.00
0.04

0.00
0.00
0.00
0.00
0.00
0.00
3.02
0.00
0.00

-0.42
0.26
3.77
-4.29
O.II
-0.16
0.16
-0.11
1.78

0.00
0.00
0.00
6.17
0.00
0.00
0.00
0.00
0.00

0.40
-0.05
-0.26

O.II
-0.05
0.00

0.18
-0.02
-0.13

0.00
0.00
0.00

0.69
-0.12
-0.39

0.04

0.00

0.02

0.00

-0.26
5.22
0.00
0.27

-0.06
0.89
0.00
0.06

-0.13
-2.28
4.72
0.12

0.00
3.26
0.00
0.00

-0.71
0.71
4.07
0.26
0.26
0.85
5.61
4.23
3.30

Female

Male

97

Total

0.06
-0.45
7.09
4.72
0.45

Table 6 (continued)
Size
group

II

ill

Duration ofrearing(days)

MuscleHepat.

Integ.

Exu.

Gonad

Spawn

MuscleHepat.

Integ.

Exu.

FemaleMale

59 (Dec-Feb)
61 (Feb-Apr)
59 (Apr-June)
6 (June-June)
56 (June-Aug)
27 (Aug-Sept)
9 (Sept-Sept)
28 (Sept-Oct)
70 (Oct-Dec)

0.13
0.13
0.85
-1.64
0.31
0.57
2.93
1.24
0.13

-0.83
0.61
-0.72
-0.28
-0.28
0.95
0.55
-0.83
2.06

0.04
0.05
0.35
-0.66
0.12
0.23
-3.52
5.16
0.05

0.00
0.00
0.00
0.00
0.00
0.00
3.93
0.00
0.00

-0.89
0.47
8.37
-9.46
0.26
-0.37
0.16
-0.21
2.98

0.00
0.00
0.00
9.54
0.00
0.00
0.00
0.00
0.00

0.62
-0.09
-0.40

0.11
0.00
-0.11

0.28
-0.04
-0.18

0.00
0.00
0.00

1.01
-0.13
-0.69

0.09

0.05

0.05

0.00

-0.49
4.92
0.04
0.31

-0.11
0.95
0.00
0.05

-0.23
-3.92
6.09
0.15

0.00
4.27
0.00
0.00

-1.55
1.26
8.85
-2.50
0.41
1.38
4.05
5.36
5.22

59 (Dec-Feb)
61 (Feb-Apr)
59 (Apr-June)
6 (June-June)
56 (June-Aug)
27 (Aug-Sept)
9 (Sept-Sept)
28 (Sept-Oct)
70 (Oct-Dec)

0.17
0.18
1.15
-2.21
0.40
0.79
2.04
1.46
0.22

-1.22
0.95
-1.17
-0.34
-0.39
1.34
0.44
-1.16
2.78

0.06
0.09
0.42
-0.83
0.14
0.31
-4.84
6.18
0.08

0.00
0.00
0.00
0.00
0.00
0.00
4.76
0.00
0.00

-1.46
0.83
13.86
-15.74
0.47
-0.63
-0.26
0.06
4.28

0.00
0.00
0.00
12.68
0.00
0.00
0.00
0.00
0.00

0.93
-0.13
-0.58

0.17
0.00
-0.11

0.39
-0.05
-0.24

0.00
0.00
0.00

-2.45
2.05
14.26
-6.44
0.62
1.81
2.14
6.54
7.36

1.49
-0.18
-0.93

FemaleMale

Metabolic loss The amount of oxygen consumption in eachindividual housed in a plastic chamber was measured by the
Winlder method for 7-9 shrimp of various sizes. A regression equation among oxygen consumption per unit time,
water temperature, and body weight was obtained (Fig. 13).
From this equation and monthly mean values of body weight
and water temperature, monthly oxygen consumptions were
calculated. The standard metabolism in terms of caloric value
was determined by multiplying the oxygen consumption by
4.83 cal/mL-02 (Ivlev 1934).
The amount of metabolic loss was assumed as twice thestandard metabolism from the literature (McLeese 1964,
McFarland and Pickens 1965, Nelson et aI. 1977a,b, Loganand Epifanio 1978) in which specific dynamic action andswimming were considered (Table 7).
The amounts of energy released for metabolic activity arein the range of 0.46-0.76 kcal' day- \. ind:- 1 during Juneand October, and are under 0.4 kcal' day - \. ind:- I during
the winter period of inactive feeding, unrelated to differences
in body size or sex.

5

Total

-0.13

0.00

0.05

0.00

0.66
3.56
0.05
0.40

-0.11
0.94
0.00
0.06

-0.29
-5.35
7.30
0.16

0.00
5.18
0.00
0.00

0.19
-0.83
6.22
6.13
0.51

0.18
-1.06
4.33
7.35
0.62

logR = log(O.0523 t -O.0415)+O.2881logW

CD

+'

III
M

~

t- o

0

+'

III
M

....P.
CD
'"
p::

I
.--4

S

1

Body weight

50
g:wet

Figure 13
Logarithmic plots of respiratory rate against body weight•• 9.0°C;
o USC; • IS.O°C; /:;. 19.2"C. The base of logarithms in this equation is 10.

Assimilation The equation for the amount of assimilation
was G + R = A (Table 6).

of assimilation divided by these efficiencies gave the bimonthly values of consumption (Table 7).
Seasonal variations of ingestion energy shown in Table 7
generally have the same tendencies as that of the daily
amounts of food eaten shown in Table 4.

Consumption In this paper, food consumption is calculated
by A/assimilation effeciency. From the monthly values ofdaily ingestion the daily defecation rates obtained with theunits of weight in Table 4 and the caloric values of euphausids (6.05 kcal' g dry wt - I) and defecations (5.09 kcal' g
dry wt- 1), the assimilation efficiency was calculated interms of caloric value (Table 8). Further, the monthly values

98Table 7
Food energy distribution in mantis shrimp, expressed in kilocalories.

Group

II

III

Metabolic loss

Total growth

Assimilation energy

Ingestion

Egestion

(R)

(G)

(A)

(C)

(E)

Duration ofrearing(days)

FemaleMale

FemaleMale

FemaleMale

FemaleMale

FemaleMale

59 (Dec-Feb)
61 (Feb-Apr)
59 (Apr-June)
6 (June-June)
56 (June-Aug)
27 (Aug-Sept)
9 (Sept-Sept)
28 (Sept-Oct)
70 (Oct-Dec)

17.40
17.10
22.78
2.78
29.84
16.22
5.58
17.18
34.04

17.56
17.30
22.78

-0.71
0.71
4.07
0.26
0.26
0.85
5.61
4.23
3.30

0.69
-0.12
-0.39

16.69
17,81
26.85
3.04
30.10
17.07
11.19
21.41
37.34

18.25
17.18
22.39

20.45
19.70
29.06

22.37
19.00
24.23

3.76
1.89
2.21

4.12
1.82
1.84

33.16

34.48

34.51

1.34

1.35

15.85
12.73
22.12
34.75

17.76
11.60
22.63
41.91

16.49
13.19
23.38
39.11

0.69
0.41
1.22
4.57

0.64
0.46
1.26
4.36

59 (Dec-Feb)
61 (Feb-Apr)
59 (Apr-June)
6 (June-June)
56 (June-Aug)
27 (Aug-Sept)
9 (Sept-Sept)
28 (Sept-Oct)
70 (Oct-Dec)

19.66
19.30
25.74
3.14
33.70
18.32
6.14
18.60
36.82

-1.55
1.26
8.85
-2.50
0.41
1.38
4.05
5.36
5.22

1.01
-0.13
-0.69

20.87
19.39
25.03

18.86
21.55
36.76

21.74
20.32
26.60

0.75
0.99
2.17

0.87
0.93
1.57

37.57

35.86

38.77

1.11

1.20

17.59
12.44
25.01
37.61

20.39
10.73
25.49
44.53

18.21
13.09
26.61
39.84

0.69
0.54
1.63
2.49

0.62
0.65
1.60
2.23

59 (Dec-Feb)
61 (Feb-Apr)
59 (Apr-June)
6 (June-June)
56 (June-Aug)
27 (Aug-§ept)
9 (Sept-Sept)
28 (Sept-Oct)
70 (Oct-Dec)

21.24
20.88
27.86
3.40
36.42
19.82
6.58
19.68
38.94

22.95
20.94
26.87

20.95
29.66
45.39

25.59
27.09
32.19

2.16
6.73
3.27

2.64
6.15
5.32

40.60

36.13

43.15

2.13

2.55

18.84
10.97
27.31
39.88

23.41
9.30
28.28
49.20

20.39
11.70
29.46
42.38

1.78
0.58
2.06
2.90

1.55
0.73
2.15
2.50

33.10
16.30
5.64
17.40
34.30
19.86
19.52
25.72
37.38
18.42
6.22
18.88
37.10

-2.45
2.05
14.26
-6.44
0.62
1.81
2.14
6.54
7.36

21.46
21.12
27.80
40.42
19.90
6.64
19.96
39.26

0.06
-0.45
7.09
4.72
0.45

0.19
-0.83
6.22
6.13
0.51
1.49
-0.18
-0.93
0.18
-1.06
4.33
7.35
0.62

Assimilation efficiencies (%) of mantis shrimp
size groups calculated in terms of caloric value.
Size group

Dec
Jan
Feb
Mar
Apr
May
June
July
Aug
Sept
Oct
Nov
Dec

91.9
72.2
92.1
87.9
94.4
90.1
96.1
96.2
96.0
96.5
92.3
83.4
94.3

II

ill

95.0
96.0
98.2
94.0
94.6
92.5
98.7
95.6
97.1
95.0
92.9
93.4
97.0

96.2
94.4
60.0
84.6
86.7
95.8
95.3
93.9
92.0
93.8
91.5
96.8
92.7

18.79
22.93
42.12
-3.04
37.04
21.63
8.72
26.22
46.30

Egestion The equation for the amount of egestion was
C - A = E (Table 7). Tables 6 and 7 present the seasonalvariations of energy budgets per about a two-month period
in terms of consumption, assimilation, accumulation, andegestion of energy. In the sum of these values, the energy
budgets for the year are shown in Table 9.
In adult shrimp, a total of 190-240 kcal per year are
ingested and about 90% is assimilated. Almost all theassimilated energy is lost by metabolism, and the remaining
energy (19-26 kcal in females, about 12 kcal in males) is
accumulated in each body component, of which 7-14 kcal
is used for growth of the ovary and 85-90 % is released fromthe body as reproductive substances at spawning. Gross
growth efficiencies are indicated 9-11 % in females and 5-6 %in males.
Further, if quantitative changes in growth and food consumption of larva and young are investigated on the basisof the above methods, the life history of mantis shrimp will
be clarified.

Table 8

Month

18.11
20.56
34.59
0.64
34.11
19.70
10.19
23.96
42.04

99

Table 9
Energy budget in the mantis shrimp.
Group IIGroup I
(Kcal/year)
Food
Food ingested
Feces excreted
Food assimilated
Metabolic loss
GrowthTotal
MuscleHepatopancreas
Inte~~ent

EXUViae
Gonad
Gametes ejected

CitationsGroup III

FemaleMale

FemaleMale

FemaleMale

197.5916.09
181.50162.92

192.2815.85
176.43
164.38214.1710.27
203.90181.42205.189.67
195.51
183.10242.3221.61
220.71
194.82231.9523.59
208.36
196.56

18.58
5.01
1.17
2.11
3.02
1.10
6.17

12.05
5.36
0.95
2.48
3.26

22.48
4.65
1.23
1.82
3.93
1.31
9.54

12.41
5.00
0.94
2.20
4.27

25.89
4.20
1.23
1.61
4.76
1.41
12.68

11.80
3.70
0.95
1.97
5.18

_

Harding, J.P.
1949 The use of probability paper for the graphical analysis of polymodal frequency distributions. J. Mar. BioI. Assoc. U.K. 28:
141-153.
Hiatt, R.W.
1948 The biology of the 1ined shore crab. Pachygrapsus crassipes Randall. Pac. Sci. 2: 135-213.
Ivlev, V.S.
1934 Eine mikromethode zur bestimming des kaloriengehalts non
nahrstoffen. Biochem. Zool. 275:49-55.
Kurata, H.
1960 Increase in size at moulting in Crustacea. Bull. Hokkaido Reg.
Fish. Res. Lab. 22: 1-48.
Logan, D.T., and C.E. Epifanio
1978 A laboratory energy balance for the larvae and juveniles of theAmerican lobster HoTTUJrus americanus. Mar. BioI. 47:381--389.
McFarland, W.N., and P.E. Pickens
1965 The effects of season. lemperature, and salinity on standard andactive oxygen consumption of the grass shrimp, Palaemonetes vulgaris(Say). Can. J. Zool. 43:571-585.
McLeese, D.W.
1964 Oxygen consumption of the lobster, Homarus americanus MilneEdwards. Helgol. Wiss. Meeresunters. 10:7-18.
Nelson, S.G., A.W. Knight, and H.W. Li.
1977a The metabolic cost of food utilization and ammonia production by juvenile Macrobrachium rosenbergii (Crustaces:Palaemonidae). Compo Biochem. Physiol. 57A:67-72.
Nelson, S.G., H.W. Li, and A.W. Knight1977b Calories, carbon and nitrogen metabolism of juvenile Macrobrachium rosenbergii (De Haan) (Crustacea, Palaemonidae) withregard to tropic position. Compo Biochem. Physiol. 58A:319-327.
Yamazaki, M.
1985 Food consumption of the mantis shrimp, Oratosquilla oratoria(De Haan). Bull. Fac. Fish. Hokkaido Univ. 36:177-181.
Yamazaki, M., and A. Fuji
1980 Reproductive cycle of the mantis shrimp, Squilla oratori(l deHaan, in Mutsu Bay. Bull. Fac. Fish. Hokkaido Univ. 31:161--168.

100

Growth and Survivalof Artificial Abalone
Seed Released in
Shijiki Bay, Japan

Abalone is a major fishery of rocky coastal Japan, priced
at about 5000 yen/kg. Annual catches from 1975 to 1984
were between 3900 and 5650 tons. Total world catch in 1982
was approximately 20,000 tons. Japanese consumption of
abalones is estimated at about 9000 tons. Japan leads inabalone consumption and is the second leading producer,
after Australia (Uki 1985). The catch in Japan consists
primarily of four species: Haliotis discus hannai occurs in
the north, while the other species, H. discus, H. gigantea,
and H. sieboldii, range from the central to the southern
regions. Propagation of abalones through fishery management and protective breeding has had a long history in Japan.
Recently, sea farming techniques of releasing hatchery seed
have been developed. The number released in 1983 amounted
to 17.5 million, composed of 64 % H. discus hannai and 34 %H. discus. The shell length of seeds at release was approximately 30 mm.
In many cases, however, it is not clear whether the releasing of seeds results in increased catch. The growth rateand survival rate of artificially produced young abalone,
H. discus, on the fishing ground was determined in orderto develop a method for evaluating its ecological and biological characteristics.

KIYOKAZU INOUE
Seikai National Fisheries Research Institute49 Kokubumachi
Nagasaki 850, Japan

ABSTRACTThe growth rate and survival rate of artificially produced young
abalone, Haliotis discus, on the fishing ground was determinedin order to develop a method for evaluating its ecological andbiological characteristics. Daily growth {Jlm/day) decreased during the period with the high water temperature. The mean daily
growth differed between the two stations. Survival rates decreased throughout the experiment, and the largest decrease
occurred just after release.

Materials and methods_

Two experimental stations, A and B, were located in Skijiki
Bay, Hirado island, in southern Japan (Fig. 1). The duration of the experiment was 20 March-25 September 1986.

0

130 E

132"E

Figure 1
Location of experimental stations, Shijiki Bay, southern Japan.

101

20

GROUP

y

150

ALL

10

ST. A
0-0

. - - . GROUP M

0

E 100

~

GROUP M:;:

RECAPTURED

10

0

a:

"
>-

>-

U

W

0--0

:I:
I-

~

Z

ST. B

.3-

20

-.

GROUP Y

..J

<i
c

0

::::>

0
w
a:: 2050

GROUP M

u.

ALL

10

0

0

M
1986

20

OL..L--'----L..L-L-.L.....L--'-.L...L---'---'---'=-

25

35

M

J

J

A

S

Figure 3

RECAPTURED

10

A

Seasonal changes in daily growth of abalone seed.

-'--

45

September. Samples were collected by two or three SCUBA
divers for two hours each time. Color and number of thetags, shell length and body weight were determined. Measured abalones were taken to their former station and released
carefully, but randomly, in order to obtain an accurate
analysis.
Growth rate was indicated as daily growth (J.an/day) ,calculated by dividing the increase of shell length by the days
between release and recapture. This calculation used only
the data of individuals recaptured in consecutive samplings.
Survival rate was calculated from the total number released
initially and the total number in the population estimated ateach sampling. Total number in the population was estimatedby Jolly-Seber's multiple recapture method.

SHELL LENGTH (mm)Figure 2
Distribution of shell length of abalone seed at release and recapture.

Station A was a pile of stones surrounded by sand at a depthof about 7 me~ers. It had some sargassum and other small
seaweeds. The sargassum decreased after July, in the typicalseasonal pattern. Some natural juvenile abalones lived in
Station A. The area of the rock pile was about 150 m2 andthe height was about 1.5 m. Station A was selected because
the surrounding sand would prevent dispersion of the planted
abalones. Station B was on a rocky coast with much seaweed
at a depth of 1-5 meters. The seawood was mostly sea oak,Eisenia bicyclis. Station B was considered a suitable environment for abalones and was selected to compare its growthrate with Station A.
The abalones, all H. discus, used in this study were obtained from Yamaguchi Prefecture (Group Y) and Miyagi
Prefecture (Group M). Initial mean shell lengths were 31.5mm and 29.2 mm, respectively. The numbers released at
Station A were 996 of Group Y and 985 of Group M. Numbers released at Station B were 75 of Group Y and 315 ofGroup M. Individuals were distinguished by the color andnumber of a tag attached to the shell by adhesive.
Seeds were released by SCUBA divers on 20 March andsampled four times: 23 April, 27 May, 22 August, and 25

Results_

The numbers of abalone recaptured at Station A were 217
on 23 April, 156 on 27 May, 44 on 22 August, and 20 on
25 September. Distribution of shell length of all individuals
measured at initial release was compared with that of therecaptured individuals for groups Y and M (Fig. 2). In GroupY, both distributions are similar; however, in Group M, inthe distribution of recaptured individuals, the smallest ones
were virtually absent.

102

Table 1
Population of artificial abalone, H. discus, estimated by Jolly-Seber process.
No. recaptured
Time at release (i)Time at recapture (j)No. captured

1
2
3
4
5

100

ni

No. released
Si

i=1

2

1981
212
153
42
20

1981
208
152
42
19

212
110
21
10

43
7
4

Discussion•

Estimated population
Ni

755
552
210
4

_

Apparently, artificial seed varies in biological character when
produced by different hatcheries. In this experiment, it wasdetermined that daily growth and size distribution of recaptured individuals differed between groups Y and M. To
go further in this field, it will be necessary to study the
relationship between ecological character and production
conditions.
The difference in daily growth between the two stations
was experimentally confirmed. Although the growth rate is
known to be altered by living conditions (Uki 1981, Inoueet al. 1986), the present experiment can be useful as a method
for selecting a sea farming area. For that purpose it isnecessary to obtain further data on growth rate and its
seasonal variation in young abalone under natural conditions.

~

w

50

...J

<l:

>
>
a:

::l

en

0
M
1986

14
2

4

o--oGROUP Y"-GROUP M

~
a:

3

A

M

J

J

A

S

Figure 4
Seasooal clumges in survival rate or abalone seed.

Citations_Inoue, K., H. Kito, N. Uki, and S. Kikuchi
1986 Influence of the high temperatur~ on the growth and survivalof three species of abalone. Bull. Sekai Reg. Fish. Res. Lab.
63:73-78.
Kato, F.
1978 An HPL (Hewlett-Packard Language) calculator program for
capture-recapture stochastic model of G.M. Jolly. Bull. Jpn. Sea
Reg. Fish. Res. Lab. 29:283-290.
Uki, N.
1981 Food value of marine algae of order laminariales for growthof the abalone, Hallads discus hannai. Bull. Tohoku Reg. Fish. Res.
Lab. 42:19-29.
1985 Recent status of abalone fisheries and studies in the foreign
shores. Nihon Suisanshigen Hogo Kyokai Geppou 251:5-16.

Daily growth of every group at each station decreased
throughout the experiment (Fig. 3). Especially during 22
August-25 September, the period with the highest watertemperature, there was no sign of increase in shell length
at Station A. Also, the mean daily growth of Group M at
Station A was always larger than that of Group Y, except
for the period 22 August-25 September. In comparison,
Station B had much more daily growth in Group M.
In the Jolly-Seber model, mhj, number caught in the ith
sample last captured in the hth sample, were recorded inTable 1. Total number in the population was calculated fromthat table, estimated by a personal computer program (Kato
1978).
Survival rates of groups Y and M decreased throughout
the experiment, and the largest decrease occurred just after
release (Fig. 4).

103

Copepod Swarms
Observed by SCUBADiving in a Small Inlet

of Kyushu, JapanIn Shijiki Bay, pelagic larvae of red sea bream migrate into
the Bay from offshore waters during April to May andbecome demersal. In the Bay, stomachs of demersal juveniles
are fIlled with Acartia omorii and A. steueri (Tanaka 1985).
These copepods, important food organisms for fish in a
neritic society, have swarming characteristics.
Copepod swarms have been observed in dense crowds at
specific spots in the neritic waters of the tropical, subtropical,
temperate regions, and freshwater lakes of the Arctic as well.
Many species in the genera Oithona, Acartia, Centropages,
and lAbidocera appear in swarming communities in neritic
waters (Emery 1968, Hamner and Carleton 1979, Omori and
Hamner 1982). Swarms of Heterocope septentrionalis andDiaptomus tyrrelli also occur in freshwater lakes (Hebert
et al. 1980, Byron et al. 1983). Veda et al. (1983) reported
swarms of the copepod genera Acartia, Oithona, and lAbidocera in the coastal waters of Japan.
Copepod swarms on the sea bottom must playa major rolein the food strategy of juveniles of demersal fishes. In Shijiki
Bay, copepod swarms were observed fragmentarily in 1978
and 1980 by Veda et al. (1983). Therefore, in the Bay, theauthor has intensely investigated copepod swarms to learn
the seasonal changes in distribution, locality, and size ofswarms in the various areas.

1

KATSUNORI KIMaro
Seikai National Fisheries Research InstituteFisheries Agency
Kokubu-machi 49
Nagasaki 850, Japan

ABSTRACTSwarms of copepods were observed by SCUBA diving in Shijiki
Bay, southwest of Hirado Island, western Kyushu, Japan, during early spring to midsummer 1984--85. Copepods were densely
distributed just above the sea bottom in the daytime and formed
various features of swarm according to the confJgUl'ation of sea
bottom and season. Seven swarming copepod species, Acartia

omorii, A. steueri, A. sinjiensis, Oithona oculaJa, 0, davisae, Tor-

Copepod swarms/anus longipes, and T. TUbUlus, were identified. Each swarm consisted of many copepodite stages, sometimes pf a single species
but also of a mixture of several species. Species, stage and sex
composition, shape of swarm, and swarming location varied
seasonally. The swarm maintained a stationary spatial position
when the water current was weak. Swarming of Acartia andOithona may serve as an important food for some juvenile
demersal fIShes during their early demersal stages.

_

Copepod swarms were observed and collected at Shijiki Bay,
southwestern Hirado Island, western Kyushu, Japan, from
May to August 1984 and 1985 (Fig. 1). Repeated obser-

eS-9

eS-8
eS-7
Shlomibono

e5-2

S~'

eS-3

eS-4

,L-I

,L-2

..

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~-5(

S.;5

L-3
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S-6 /L-4

0.5
,

,I km

Figure 1
Location of stations in Shijiki Bay, southwest of Hirado I., western Kyoshu, Japan. Stations with slanted bar indicate where rope line was set.

'Contribution No. 439 of the Seikai National Fisheries Research Institute.

105

Table 1
Copepod swarms observed by SCUBA diving in Shijiki Bay.
Depth (m)Species

Shape and size of swarm

Acartia omorii

A. steueri
A. steueri + Oithona oovisae
O. oculata

Continuous flat swarm, 5-30 em thickIrregular balls, 10-30 em diameter
Continuous flat swarm, 5-30 em thickIrregular balls, 10-50 em diameter
Irregular balls, 10-50 em diameter
Irregular balls, 10 em-3 m diameter
Irregular balls, 10 em-l m diameter
Irregular balls, 30-50 em diameter
Irregular balls, 10-30 em diameter

10-27
10-24
10-18
10-13
7
2-7
2-7
3
2-7

O. oculata + A. sinjiensis
Tortanus longipes + T. rubidusBall, 10 em diameter
Column, 20 em diameter, 50 em height4
2

A. omorii + A. steueri

Swanning location
Over flat sandy bottom
Over flat sandy and gravelly bottom
Over flat sandy bottom
Over flat sandy bottom
Over and throughout entire Zostera bed
Over rocky shore, around algal bed
Over and throughout entire Zostera bed
Edge of Zostera bed
Inside Zostera bed, over rocky shore andgravelly bottom
Edge of Zostera bed
Edge of Zostera bed

aAcartia omorii
Acartia steueri

Acartia omorii

Current

Acartia steueri
Oithona oculata

5-30cm.s=t:.;i\.:.:.)".

oithona oculata
Oithona davisae

t~.~.~:~g;::~~~!:i e~Y';'i.'~.:. ::; .::'':-:':::"""

Sandy bottom
Zostera marinac
Ecklonia stolonifera
EiseniabicycliGravelRocky I"eef
GravelBoulder-shingle
bottomFigure 2
Schematic illustrations of copepod swarming relative to bottom topography and materials in Shijiki Bay. a) Sandy bottom, b) Zostera marina bed,c) shoal of small rocks with brown algae, d) shoal of large rocks with brown algae.

A total of seven species of three genera were identified
from swarming copepod communities; three species ofAcartia,of Oithona, and two of Tortanus (Table 1). A
swarm sometimes consisted of a single species or genus andsometimes not. Species, stage, sex composition and shapeof swarm, and swarming location varied seasonally.

were made by SCUBA diving along a 50-m long graduatednylon rope set on sandy bottom and eelgrass (Zostera marina)
bed, 4-12 m in depth (L stations, Fig. 1). Observations werealso made occasionally at gravelly and sandy bottom, 6-35
m in depth (S stations, Fig. 1). Swarming copepods werecollected with a Van Dom water sampler (6 L) or plastic
suction bottle (3 L) like a syringe, and a hand-operated
plankton net (50 ~m mesh opening).

twf

106

200

[J A.omorii

o

150
0<

';;;
0

::l

"0
.:;:

400

~ A.steuer; CD-CVl-

Acortio spp. N - CI

~

'>0
I

tl

"-

:;

300

"on

g 200

100

"0
.:;:

"0

~

50

100

100

100

80

~
:; 80
0

60

I

"-

:; 40
0

20
100

20
100

~
:;

80

0

60

0

60

40

0

40

~

C

:;:

..
.

"-

~

..
0

E

b

60

G

40

0

"-

a

D A.omor;; Cll-CVl
D Acortio spp. N - CI

CD-CVlii~~ A.steuer; CD-CVl

aE-A.steuer;_.- A.omorii

l.L.

20

l.L.

20

0
12
Ma y

A.steuer;

80

II
June

21

0

II

I

12

Jul y

May

II
June

21

II
Jul y

Figure 3

Figure 4(a) Seasonal changes in number of Acarlia steueri and A. omorii, andpercentages of (b) adults and (c) females in each species of Acarlia
collected by horizontal tow with plankton net at flat sandy bottom of
inner part of Shijiki Bay, 12 May-13 July 1984.

(a) Seasonal changes in number of Acarlia steueri and A. omorii, andpercentages of (b) adults and (c) females in A. steueri collected byhorizontal tow with plankton net at eelgrass (Zostera nuuina) bed ofinner part of Shijiki Bay, 12 May-13 July 1984.

Acania omorii and A. steueri formed continuous flatswarms usually 5-30 cm thick, just above the flat sandy
bottom in shallow waters 10-27 m depth (Stn. L-1, 2, S-l,
3, 5, 7, 8; Fig. 2a) from spring to early summer. Thickness
and density of copepod swarms varied from place to place,and may be affected by the configuration of sea bottom andcurrent strength. In the Bay, copepods sometimes formeda small ball or disk-shaped swarm. The sizes of swarms
ranged from 10 cm to a few meters in diameter, but boundaries between swarm and background were not always clearly
defined.
Copepod swarms were often observed in the lee of objects
on the bottom such as clumps ofliving or dead algae, rocks,
and trash. Swarm organisms usually held the same spatial
position and swimming pattern against a moderate current.
But when the current was stronger than about 5 cm/s,
copepods were carried away from their initial position by
the current.
Copepods swarm upward with a spiral movement and theswarm dispersed throughout the water column immediately
after sunset. After sunrise the next morning, they swam
downward and formed a swarm on the sea bottom again.

A. steueri and A. omorii in swarms on flat sandy bottom
were collected by horizontal tow of a plankton net. A numberof organisms, including all developmental stages of adults,
copepodites and nauplii, ranged from 8 to 190 per liter (Fig.
3a). This value is much higher than that collected by an ordinary plankton-net vertical haul. The ratio of adults (CVI)
to copepodites (Crr to CVI) for the above two species varied,
but the mean was about 60 percent (Fig. 3b). Females ofboth species comprised about half of the adults (Fig. 3c).
At eelgrass (Zostera marina) beds with a range of 2-7 m
in depth (Stn. L-3, 4, 7, 9,10, S-l; Fig. 2b), dense swarmsof A. omorii and A. steueri were observed during the observational period from March to July. Copepods swarmed
within and near the eelgrass bed from the roots up to above
the grass blades. Density of organisms, consisting of adults,
copepodites, and nauplii, collected by the horizontal net towing inside the swarm ranged between 14 and 342 per liter(Fig. 4a). In Acania swarms, adults were abuandant andfemales far outnumbered males, particularly in July (Fig.
4b, c). Acartia often swarmed in high densities along theedges of Zostera beds.

107

In the lee of rocks and brown algae, Ecklonia stolon!fera,
on a shoal (Stn. S-2, 4; Fig. 2c) 15-20 m deep in the central
part of the Bay, A. omorii formed ball-shaped swarms witha diameter of 10-30 em. On the other hand, in shoals nearshore, 2-7 m deep in the inner part of the Bay, A. omoriiand A. steueri formed large dense swarms in the lee of rocks
and beds of brown algae (E. stolonifera, Eisenia bicyclis,
and Sargassum spp.) (Stn. S-6, L-5, 6; Fig. 2d). Theseswarms were diverted right and left by waves. When disturbed by divers, they quickly resumed their initial position.
In summer, Oithona oculata formed swarms at a rocky
reef and a Zostera bed in the inner part of the Bay (Stn. S-6,
L-4, 9, 10). The Oithona swarm was ball-shaped with adiameter of 10 cm-1 m. Density of the O. oculata swarm
was higher than that of Acartia, ranging from 490 to 6490
individuals per liter. A small ball-shaped swarm, consi~tingof O. oculata and Acartia sinjiensis, and large swarms, consisting of Oithona davisae and A. steueri, were also formedat the edges of the Zostera bed.
A small cylindrical swarm of Tortanus longipes and T.
rubidus was observed at the edge of the Zostera bed. In theswarm, organisms moved in a swirl and maintained a cylindrical configuration.

Swarming processes and functionsof copepod swarms

are probably able to recognize other individuals by chemical(Katona 1973), optic, and physical stimuli and fulfill someorganic functions.
Adaptive functions of copepod swarms were suggested byprevious authors (Hamner and Carleton 1979, Omori and
Hamner 1982, Veda et al. 1983). Hamner and Carleton(1979) suggested four adaptive functions: Protection frompredators, facilitating breeding, maintaining a favorable position to feed on coral mucus, and restricting dispersion by
currents. They suggested that, although protection frompredators was the most common and important adaptive explanation for copepod swarming, all these adaptive functions
were responsible for denser populations on coral reefs.
The importance of these adaptive functions may vary
among species. Reduction of dispersion by currents appears
to be of major importance for the swarms in maintaining
populations of copepods. On the other hand, swarming probably poses a contradiction: When swarming organisms are
distributed at the same space and time as demersal fishes,
copepods tend to be eaten by fishes. Predation of A. steueriand A. omorii by demersal juveniles of red sea bream wasobserved in the Bay (Tanaka 1985). This suggests that thejuveniles feed effectively on swarming Acartia, and, therefore, that copepod swarms are important in the feeding
strategy of some fishes during their early demersal life.
Copepod swarms could be induced by certain artificial structures constructed on the sea bottom; thus it may be possible
to design a new nurseryground for juvenile fishes in the
future.

_In Shijiki Bay, swarms consisted of many copepodite stages,
sometimes of a single species but also of a mixture of several
species. The density of a swarm was much higher than thatcollected by ordinary vertical hauls of plankton net. Swarming during the day, copepodites of Acartia spp. and Oithonaspp. aggregated to a density several hundred times denser
than the mean density. However, the density changed bothseasonally and daily, probably caused by seasonal population change and weather or tidal current conditions.
Present results suggest that copepod swarming is closely
related to the rnicrobottom topography and some materials
on the bottom. The author also observed a copepod swarm
on artificial materials, e.g., a gill net for crab fishing set on
sandy bottom. Furthermore, the author could induce copepood swarms by field experiments with plastic boxes ofdifferent sizes (Kimoto unpubl.). Two processes of swarming by copepods were suggested: First is the increasing
copepod density near-bottom by day during their diurnal vertical migration; second is that copepods swimming near thebottom are concentrated and form a much denser swarm in
the lee of materials such as clumps of living or dead algae,
rocks, and trash. The above copepods are probably carried
into the lee by moderate currents. The spatial position of a
copepod swarm is probably maintained by the wake formed
behind the materials on the bottom. This interpretation wasmade by Kakimoto et al. (1983) who observed copepod (A.
clausi = A. omorii) and mysid (Proneomysis fasca) swarms
at natural and artificial reefs of the coastal area of Niigata
Prefecture, Japan Sea. Copepods gathered at a certain density

Acknowledgments_

The author is grateful to Dr. F. Koga and Dr. Y Moriokaof this Laboratory for encouragement and valuable suggestions in the above research and int~rpretation of results.
Zooplankton sampling operations at sea were conducted withthe assistance of J. Nakashirna and crew members of the R/VYoukou Maru of the Seikai Regional Fisheries Laboratory.
Thanks are also due to the members of the Shijiki Fisheries
Cooperative Association, Hirado, for their interest and facilities for field work.
This work was conducted under the research projects"Marine Ranching Program" (MRP 87-IV-2-1) and"Coastal Fishing Ground Improvement and Development
Program" supported by the Ministry of Agriculture, Forestry
and Fisheries.

108

Citations_

Byron, E.R., P.T. Whitman, and C.R. Goldman
1983 Observations of copepod swarms in Lake Tahoe.
Oceanogr. 28:378-382.
Emery, A.R.
1968 Preliminary observations on coral reef plankton.
Oceanogr. 13:293-303.

LimnoI.

LimnoI.

Hamner, W.M., and J.H. Carleton
1979 Copepod swarms: Attributes and role in coral reef ecosystems.
LimnoI. Oceanogr. 24: 1-14.
Hebert, P.D.N., A.G. Good, and M.A. Mort
1980 Induced swarming in the predatory copepod Heterocope septentrionalis. LimnoI. Oceanogr. 25:747-750.
Kakimoto, H., H. Ookubo, H. ltano, and K. Arai
1983 Gyoshou ni okeru doubutsu purankuton no bunpu yousiki ni tuite(Distribution of zooplankton at artificial reefs). Fish. Eng. 19:21-28[in Jpn.].
Katona, S.K.
1973 Evidence for sex pheromones in planktonic copepods. LimnoI.
Oceanogr. 18:574-583.

Omori, M., and W.M. Hamner1982 Patchy distribution of zooplankton: Behavior, population assessment and sampling problems. Mar. BioI. 72: 193-200.

Tanaka, M.
1985 Factors affecting the inshore migration of pelagic larval anddemersal juvenile red sea bream Pagrus major to a nursery ground.
Trans. Am. Fish. Soc. 114:471-477.

Veda, H., A. Kuwahara, M. Tanaka, and M. Azeta
1983 Underwater observations on copepod swarms in temperate andsubtropical waters. Mar. EcoI. Prog. Ser. 11:165-171.

109

Feeding Ecology ofYoung Red Sea Breamin Shijiki Bay

Red sea bream Pagrus major is one of the most important
demersal fishes for coastal fisheries in Japan because of its
high landings and high market price. Since the 200-milefishing jurisdiction was established, exploitation of the ocean
potential around Japan became more imperative to meet theincreasing demand for fish and shellfish of high quality.
Recently, projects of stock enhancement have been promoted
for the red sea bream through releasing operations, because
mass production of juveniles has been established for thisspecies in hatcheries. However, these releasing operations
do not appear to have always resulted in increases to red sea
bream stocks. There are two main keys to success of theseprojects: One is the qualitative evaluation of artificially
propagated fish, and the other is accurate estimation ofcarrying capacity. For the latter, it is most important tounderstand fish biology and ecology.
A series of investigations on the ecology of O-age red sea
bream has been carried out since 1975 in Shijiki Bay to provide a biological basis for stock enhancement. The" Shijiki
Project" deals with the early life history of red sea bream,fish communities, oceanographic conditions, primary andsecondary production, experimental release of artificially
propagated young red sea bream, etc.
In the present paper I explain the living modes of red sea
bream, especially feeding ecology of the young. I also
describe interspecific relationships between young red sea
bream and other fish species.

lllROYUKI SUDO 1
Seikai National Fisheries Research InstituteFisheries Agency of Japan
49 Kokubu-machi
Nagasaki 850, Japan

ABSTRACT
Feeding ecology of red sea bream in Shijiki Bay is explained
especially with (1) changes in diet with growth, (2) predatorprey interactions between young red sea bream and gammaridean amphipods, and (3) feeding relationships between young
red sea bream and other fISh species. Juvenile and young red
sea bream feed mainly on calanoid copepods and gammaridean
amphipods, respectively, in the sandy bottom area of the innerpart of the bay. They feed on calanoids when the calanoid swarm
is formed and on gammarids when the gammarid density ishighest. Crimson sea bream and stripedfm goatfISh also change
their main food from calanoids to gammarids as they grow inthe sandy bottom area of the inner part of the bay. However,the peak month of feeding on calanoids and gammarids by these
two fIShes does not coincide with that of occurrence of each prey
item in the field. Furthermore, young red sea bream always feed
mainly on gammarids, independent of coexistence with hairychin goby; hairychin goby shift their main food from gammarids to mysids in the presence of red sea bream. These facts
demonstrate that young red sea bream have an advantage overother fISh species in feeding relationships.
Gammarids are the most important prey for young red sea
bream; however, this fISh cannot feed on all gammarid species
in the field. Young red sea bream can add gammarids to theirdiet when gammarids become epibenthic. This fact points out
the importance of discriminating the "true" prey species byspecies identification of prey organisms.

Living modes of red sea breamin Shijiki Bay_

Environmental features
Shijiki Bay, about 10 km2 in area, is located at the southernend of Hirado Island in Nagasaki Prefecture, northwestern
Kyushu (Fig. I). The bottom consists mostly of well-sorted
fine sand. Zostera marina grows in the inner part of the bay
where the sandy bottom area is shallower than 7 m; Sargassum spp. grow in the reef area.
The flow pattern in Shijiki Bay indicates that the bay canbe further subdivided. Two imaginary lines, one traced
between Megasaki and Nagatenohana and another between
Shiomibana and Iidabana, divide the bay into three parts:(I) the mouth is characterized by offshore waters; (2) theinterior is characterized by proper embayed waters; and (3)the central area is characterized by a mixture of these twowater masses (Tamai 1980). These divisions are also suggested by other environmental factors (Hamada 1980, Kiso
1980a, Sudo et al. 1983). Moreover, these divisions agreewith the distribution of zooplankton fauna (Ueda 1980),
macrobenthos fauna (Azuma and Jinno 1980) and fish fauna(Nakabo 1980).

'Current address until 9/90: School of Fisheries, WH-lO, University ofWashington, Seattle, WA 98195.

111

o

sandy bottomnre~f or

II! eelgrass zone
Wbouldershingle zone'----------'

lkm

Figure 1
Map of Shijiki Bay, Japan (depth contours in meters).

_

Immigrationq

Emigration

Figure 2
Shijiki Bay is essentially open because of the strong influence of the Tsuchima Current and the absence of rivers flowing into it. However, in the interior, detritus from seagrass
accumulates on the bottom and is decomposed by bacteria
under aerobic conditions (Sudo et al. 1983). The abundantdetritus supports high productivity of benthic crustaceans,including gammaridean amphipods, and forms a healthy andfertile nursery ground for fishes in the inner part of the bay.

Growth and migration pattern of 6-age red sea bream in Sbijiki Bay(Sudo and Azeta 1986).

Growth and migration

O-age red sea bream in Shijiki Bay change their main foodwith growth in the following order as shown in Figure 3 (Kiso
1980b): calanoid copepods, gammaride,.an amphipods, mysids. Demersal juveniles occurring in the sandy bottom areaof the interior in late May feed mainly on calanoid copepods
swarming near the bottom (Tanaka 1985). From June throughAugust, when juveniles and young are most dense there, they
feed heavily on gammaridean amphipods. These changes indiet appear to be related closely not only to prey size but
also to prey density. Red sea bream feed on calanoid cope- .
pods when the calanoid swarm is formed and on gammaridean amphipods when the gammarid density is highest (Fig.
4). Furthermore, young red sea bream are densely distributed
at sites where gammaridean amphipods are abundant (Azeta
et al. 1980, Sudo et al. 1983). These facts emphasize that
gammaridean amphipods are the most important prey foryoung red sea bream.

Feeding habitsof young red sea bream_

Dietary changes with growth

The migration pattern of red sea bream in Shijiki Bay isclosely related to the environmental structure of the bay(Fig. 2). Pelagic larvae hatch during March-May in offshore
spawning grounds. They are transported by tidal currents
and trapped by a circular current at the mouth of the bay.
When a little larger than 10 mm in total length, larvae metamorphose into pelagic juveniles. These juveniles begin to
migrate into the bay beyond the boundary between the outerand inner water mass. After immigration into the bay,juveniles become demersal at 12-15 mm total length in late
May (Tanaka 1980, 1985).
Demersal juveniles feed on calanoid copepods swarming
near the bottom, and gradually concentrate in the sandy bottom area of the interior. There, they feed heavily on gammaridean amphipods and grow at the rate of O.7 mm per day.
In June they reach the young stage, and in August they growto 70-90 mm fork length and begin to extend their habitat
toward the central area. While extending their habitat, mysids
and other food items are added to their diet. The majority
emigrate outside of the bay for wintering in September,
although some remain in the bay until the next August (Azeta
et al. 1980, Sudo et al. 1983).

Predator-prey relationships
Sudo et al. (1987) explained diel changes in predator-prey
relationships between red sea bream and gammaridean amphipods. In Shijiki Bay, over 100 species of gammarids havebeen collected, and about 60 species of these occurred in the
112

100

Copepoda.:- 10Gammaridea

E

80
Mysidacea

....

~.

0

«
w

;;?-

0

w 60
u

a:«

z

w
a:
a:

:::l

U
U

~
~

5

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0
z

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MAMJ

JASONDJFMONTH

O'-----'---'------l.---'--.1...-----'----'----'--o 2 4 6 8 10 12 14 16
FOLK LENGTH (c m )Figure 4
Monthly changes in density of gammaridean ampbipods (mean ± 1 SD)in the sandy bottom area of the interior of Shijiki Bay April 1983February 1984. Shaded zone indicates observed copepod swarm.

Figure 3
Changes in diet of o-age red sea bream with growth (Kiso 1980b).

types. Infaunal tube-dwelling types (e.g., Byblisjaponicus)
were positively or negatively selected with diel time. Deepburrowing types (e.g., Harpiniopsis vadiculus, Urothoe sp.
B, and Urothoe sp. C) were negatively selected or hardly
consumed (Fig. 5). These results indicate that the availabilityof gammarid species increases with the decrease of gammaridliving-depth in the sediment. This finding is consistent withmy underwater observations that young red sea bream, avisual feeder, normally swim off the bottom and peck at preyorganisms only when recognizing 'them.
However, there were diel changes in the pattern of predation on gammarid species by young red sea bream. The
intensity of predation on Byblis japonicus was low about noon
but increased remarkably at dusk and dawn, whereas thaton Synchelidium miraculum lenorostralum and Paradexaminemarlie increased about noon. This diel dietary shift is causedby diel vertical movements of gammarids, because verticalmovements change their microhabitat and consequently influence their availability. Byblis japonicus, the most dominant species of gammarids in the field, lives in the tube indaytime; however, this species comes to the bottom surface
in large numbers from dusk to dawn. On the other hand, Synchelidium miraculum lenorostralum digs in the superficial
bottom sand exposing its dorsal part in the daytime, but
swims up to the water column near the bottom in large
numbers at night; Paradeximine marlie lives on the bottom
surface in the daytime but swims up the water column to nearsurface in large numbers at night. Young red sea bream cannot feed fully on Byblis japonicus in the daytime, when thisgammarid is in the tube; however, they can feed heavily on
Byblis japonicus at dusk and dawn when it is on the bottom

sandy bottom area of the interior. However, about 50 % of
gammarid species in this area occurred in stomachs of young
red sea bream. Moreover, seven species each surpassed 10%of the gammarids consumed: Byblis japonicus, Synchelidium
miraculum lenorostralum, Paradexamine marlie, Aoroides
columbiae, Melita denticulata, Gitanopsis longus, and Tiron
sp. The proportion of the sum of these seven species to total
gammarids in the stomachs ranged from 61.8% to 94.7%
with diel time. Of these seven, Byblis japonicus was the mostimportant prey species, because it was the most frequently
consumed and largest in body length. Synchelidium miraculum lenorostralum, Paradeximine marlie, and Melita denticulata were also important prey species, because of theirhigh frequency of occurrence and their large body size.
Comparing relative abundance of gammarid species in thestomachs with that in the field, individual gammarid species
were not consumed relative to their abundances in the field.
This difference between gammarid composition in thestomachs and in the field is believed to be due to the difference in availability of gammarid species. Stoner (1979)
pointed out that amphipod selection by the pinfish Lagodon
rhomboides was related most closely to the microhabitat ofamphipod species, and important prey species were all
epifaunal types. In Shijiki Bay, the patterns of gammarid
selection by young red sea bream also correlated with themicrohabitat of gammarid species. Epifaunal (e.g., Paradexamine marlie) and shallow burrowing types (e.g., Synchelidium miraculum lenorostralum) both were positively
selected as prey, although the degree of selectivity for epifaunal types was higher than that for shallow burrowing
113

100

.

B y bl"IS japonicus

80

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Figure 5iii 200a.

Diel changes in microhabitat composition of gammarids in stomachsof young red sea bream Oeft) and in the field (right): EF, epifauna;SB, shaDow burrower; DB, deep burrower; IT, infaunal tube dweller(Sudo et aI. 1987).

L

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/

..0

·97 ·74·171 ·195·t;637·1249_

5
10

0-

0

0
0

w

0

surface or in the watetcolurnn near bottom in large numbers(young red sea bre~. cease to feed after dark). On the other
hand, they can feed, 'n Synchelidium miraculum lenorostralum and Paradexq: ine marlie in the daytime, when both
gammarids live on the bottom surface (Fig. 6). Thus, thediel dietary shift of young red sea bream does not contradict
the thesis that epibenthic gammarids are most available.
However, once gammarids come to the bottom surface, theirabundance, body size, and moving speed (swimming or
crawling) appear to become major factors influencing preyselectivity. In fact, Byblis japonicus, which was more abundant, larger in body length, and slower in movement (judging from its body shape and type of appendages) (Bousfield1973), was subjected to heavier predation by young red sea
bream than the other two gammarid species when it cameto the bottom surface.

~\.

/.~

~

~~.

/.\. .-.

o0 0./000.-::::::><::0,. .........4b~
j
0«

,

,

12

16

·~189 ·948
.422'.1476·1102 ·252510:::::::::::::Bottom::::::·:····...........

16

20

24

4

8

TIME OF DAY

Figure 6
Diel predation patterns on three ganunarid species heavily consumedby young red sea bream (upper), and diel vertical movement patternsof each ganunarid species Oower). Black bars represent hours ofdarkness. Numerals indicate number of each gammarid species coUectedby one horizontal tow of larval net in water column (Sudo et aI. 1987).

Interspecific relationships
Sudo and Azeta (1986) described the interspecific relationships of young red sea bream to other fish species bycomparing their niches. Here, in particular, I examine thefeeding relationships among fishes. The niche has three main
dimensions: time, habitat, and food (e.g., Pianka 1974,
Christiansen and Fenchel 1977). Thus, the minor habitat
among fishes is compared first and the fish species coexistent with red sea bream are picked out. Then their seasonaloccurrence patterns and food habits are compared.
According to habitat analysis of demersal fishes with theindex of interspecific overlapping (Cd) of Morisita (1959),
fishes in the interior were divided into three groups: (1)sandy bottom; (2) rocky bottom; and (3) eelgrass zone. Crimson sea bream (Evynnisjaponica), stripedfin goatfish (Upeneus bensasi) , and hairychin goby (Sagamia geneionema) as
well as red sea bream belong to the sandy bottom group.
Thus, seasonal occurrence patterns of these three species inthe sandy bottom area of the interior are compared with thatof red sea bream. Crimson sea bream and stripedfin goatfish
114

Coexist
1.0

Gammaridea

+1
x

W

~

o

z
~ 05

0

-'

•

50

5

••
50

0

500

w

>

Cl

o

z

f-

W

Ci

!I !

5

x

0::
W

Separate>ol-------'---------'---------'
May

June

-1

0

I-

:>

- +1

July

MONTH

I-

u

W

...J

Figure 7

W

Changes in diet overlap index between red sea bream and hairychingoby in the sandy bottom area of the interior of Shijiki Bay (Sudo andAzeta 1986).

a

Mysidacea

I

1~
10

•

I~l
100

100

1000

•
-1

o

o

PREY SUPPLY INDEX

differ from red sea bream in the peak month of occurrence(crimson sea bream, mid-May; red sea bream, mid-June to
mid-July; stripedfin goatfish, mid-August). On the other
hand, hairychin goby overlap with red sea bream in bothminor habitat and seasonal occurrence pattern. Moreover,these two species rank high in number among demersal fishes
every year. Thus, the food habits of hairychin goby are compared with those of red sea bream.
Hairychin goby occurring in the sandy bottom area of theinterior in late May feed mainly on calanoid copepods swarming near bottom. They then feed mainly on mysids from June
through July; in August the majority migrate to the eelgrasszone in the interior (Matsumiya et al. 1980). The diet overlap index (a) of Schoener (1970) between red sea bream andhairychin goby is highest in late May when both are few innumber, because both species feed on the same calanoid
copepods. In June, when both increase in number, however,diet overlapping becomes insignificant, and the diet overlap
index is lowest at their peaks of abundance in mid-June (Fig.
7). This is because red sea bream feed mainly on gammarids
whereas hairychin goby feed mainly on mysids.
Figure 8 shows electivity indices (Ivlev 1961) of gammarids and mysids consumed by red sea bream and hairychingoby plotted against prey supply indices (prey supply index= biomass of each prey/total number of two fish species).
As is evident from Figure 8, red sea bream prefer garnrnarids whereas hairychin goby prefer mysids, at sites where
the two fish species coexist. On the other hand, at sites where
the two fish species do not coexist, hairychin goby also preferto feed on garnrnarids.
The relation between the electivity index and the prey
supply index in Figure 8 demonstrates that red sea bream
select gammarids more strongly with the increase of gammarid supply; however, there is no correlation between mysid
selection by hairychin goby and mysid supply although
mysids are the main food for hairychin goby. Moreover,hairychin goby begin to select garnrnarids with the increase

Figure 8
Ivlev's eleetivity indices of gammarids (top) and mysids (bottom)
consumed by red sea bream (closed circle) and hairychin goby (opencircle) plotted against prey supply indices. Prey supply index = Biomassof each two prey/total number of two fish species. On the left: eleetivity indices at sites where the two fISh species coexist; on the right: eleetivity indices at sites where the two fish species do not coexist (Sudoand Azeta 1986, modified from Azuma et aI. 1983).

in gammarid supply, independent of the coexistence with red
sea bream.
These results suggest that young red sea bream always feed
mainly on gammarids, independent of the coexistence withhairychin goby; hairychin goby shift their main food fromgammarids to mysids in the presence of red sea bream. However, the degree of this food segregation varies with gammarid supply: more pronounced when gammarid supply islimited, but less pronounced or nonexistent when gammarid
supply is abundant. The term "interactive segregation" wasdefined by Brian (1956) to mean that ecological differences
between species are magnified by interaction. In practice,
however, it is often difficult to prove that segregation is adirect result of interaction or ecological divergence, as statedby Nilsson (1967). However, the process of food segregation between young red sea bream and hairychin goby inShijiki Bay shows that interactive segregation occurs between
the two species as a result of the dietary shift only byhairychin goby.

115

Citations_

Sudo, H., R. Ikemoto, and M. Azeta
1983 Studies on habitat quality evaluation of red sea bream youngs
in Shijiki Bay. Bull. Seilcai Reg. Fish. Res. Lab. 59:71-84 [in Jpn.,
Eng!. abstr.].
Sudo, H., M. Azuma, and M. Azeta
1987 Diel changes in predator-prey relationships between red sea
bream and gamrnaridean amphipods in ShijikiBay. Nippon Suisan
Gakkaishi 53:1567-1575.

Azeta, M., R. Ikemoto, and M. Azuma
1980 Distribution and growth of demersal o-age red sea bream, Pagrus
major, in Shijiki Bay. Bull. Seilcai Reg. Fish. Res. Lab. 54:259-278[in Jpn., Eng!. abstr.].
Azuma, M., and S. Jinno
1980 The bottom fauna communities in Shijiki Bay, Hirado Island-I.
An attempt at analysing habitat based on animal-sediment relations.
Bull. Seilcai Reg. Fish. Res. Lab. 54:195-208 [in Jpn., Eng!. abstr.].
Azuma, M., M. Azeta, and K. Mitsumaru
1983 Feeding interrelationships between young red sea bream andcohabiting fishes in Shijiki Bay. Bull. Seilcai Reg. Fish. Res. Lab.
59:101-118 [in Jpn., Eng!. abstr.].
Bousfield, E.L.
1973 Shallow-water gammaridean Arnphipoda of New England.
Cornell Univ. Press, Ithaca and London, 312 p.
Brian, M.V,
1956 Segregation of species of the ant genus Mynnica. J. Anim. Eco!.
25:319-337.
Christiansen, F.B., and T.M. Fenchel
1977 Theories of populations in biological communities. SpringerVerlag, NY, 144 p.

Tarnai, K.
1980 The flow pattern in Shijiki Bay-I. A pattern obtained in winter,
1975. Bull. Seilcai Reg. Fish. Res. Lab. 54:157-169 [in Jpn., Eng!.
abstr.].

Tanaka, M.
1980 The ecological studies on the larvae and juveniles of red sea
bream in Shijiki Bay-I. The horizontal distribution of the pelagic
larvae and juveniles in and outside the bay. Bull. Seilcai Reg. Fish.
Res. Lab. 54:231-258 [in Jpn., Eng!. abstr.].
1985 Factors affecting the inshore migration of pelagic larvae anddemersal juvenile red sea bream Pagrus major to a nursery ground.
Trans. Am. Fish. Soc. 114:471-477.

Veda, T.
1980 Zooplankton investigations in Shijiki Bay-I. Compositions ofzooplankton and distributions of copepodg from April to August, 1975.
Bull. Seilcai Reg. Fish. Res. Lab. 54: 171-194 [in Jpn., Eng!. abstr.].

Hamada, S.
1980 Hydrographic characteristics of Shijiki Bay.

Bull. Seilcai Reg.
Fish. Res. Lab. 54:141-155 [in Jpn., Eng!. abstr.].
Ivlev, V.S.
1961 Experimental ecology of the feeding of fishes. Yale Univ.
Press, New Haven, 302 p.
Kiso, K.
19808 The bottom topography and grain size distribution of bottom
sediment in Shijiki Bay, Hirado Island. Bull. Seilcai Reg. Fish. Res.
Lab. 54:135-140 [in Jpn., Eng!. abstr.].
1980b On the feeding habit of o-group red sea bream (Pagrus major)
in Shijiki Bay, Hirado Island-I. Sequential changes of diet withgrowth and its annual variation. Bull. Seikai Reg. Fish. Res. Lab.
54:291-306 [in Jpn., Eng!. abstr.].
Matsumiya, Y., T. Murakami, T. Suzuki, and M. Oka
1980 Some ecological observation on gobies, Sagamia geneioTiema
and Rhingobius pjlaumi, in Shijiki Bay. Bull. Seilcai Reg. Fish. Res.
Lab. 54:321-332 [in Jpn., Eng!. abstr.].
Morisita, M.
1959 Measuring of interspecific association and similarity between
communities. Mem. Fac. Sci. Kyushu Univ., Ser. E. (Bio!.)
3:65-80.
Nakabo, T.
1980 Demersal fish community in Shijiki Bay-I. Distribution of &Orne
species and division of the community. Bull. Seilcai Reg. Fish. Res.
Lab. 54:209-229 [in Jpn., Eng!. abstr.].
Nilsson, N-A.
1967 Interactive segregation between fish species. In Gerking, S.D.
(ed.), The biological basis of freshwater fish production, p. 295-313.
Blackwell Sci. Pub!., Oxford and Edinburg.

Pianka, E.R.
1974 Niche overlap and diffuse competition. Proc. Nat!. Acad. Sci.
USA 71:2142-2145.
Schoener, T.W.
1970 Nonsynchronous spacial overlap of lizards in patchy habitats.
Ecology 51 :408-418.
Stoner, A.W.
1979 Species-specific predation on amphipod Crustacea by the pinfish Lagodon rhomboides: Mediation by macrophyte standing crop.
Mar. Bio!. 55:201-207.
Sudo, H., and M. Azeta
1986 Species interrelationships on food and habitat utilization in fishesof Shijiki Bay. Int. North Pac. Fish. Comm. Bull. 47:129-141.

116

Importance of
Qualitative Evaluationof Hatchery-bred Fish
for Aquaculture

In the last decade, artificial propagation of marine animals
has been vigorously pursued with a tremendous increase intotal production and number of species raised in the hatchery(Fukuhara 1983, Kuronurna and Fukusho 1984, Nose 1985).
This phenomena resulted from the diversity of consumer
demand which promoted the releasing program to enhancecoastal fishery and aquaculture activity.
In Japan, fishermen raised fry from the egg stage for theircage cultures, whereas fish seeds for restocking are producedby the national and prefectural governments. The production of fish for releasing now totals 50 million per year. The
major species for planting are red sea bream Pagrus major,
Japanese flounder Paralichthys olivaceus, and porgy Acanthopagrus schlegeli (Fig. 1). Despite the great effort inplanting artificially reared animals, little information exists
on its effectiveness in fisheries after release into the sea. The
need for fundamental knowledge of quantity, size, and quality
is a major obstacle in considering the effect of releasing
activities. More studies on quality evaluation and releasing
techniques are urgently needed. The purpose of this paper
is to review the qualitative differences between wild andhatchery-reared fish and to emphasize the necessity of qualitative evaluation of hatchery-bred fish in aquaculture.

OSAMU FUKUHARA
Nansei Regional Fisheries Research Laboratory
Ohno. Saeki-gun.
Hiroshima 739-04, Japan

ABSTRACT
Mass production techniques for commercially important species
have advanced for a decade in Japan. Numerous hatcheryreared fish are used for not only cage culture but also forreleasing programs. However, little information exists on determining the quality and survival potential of hatchery-reared fISh.
A comparison between reared and wild fISh is a prerequisite
for the effective use of farmed fmgerlings in aquaculture activities. This paper attempts to review, understand, and contrast the biological features of hatchery-reared fISh with thoseof wild fISh and to search for the causes of those differences.
Various steps in evaluating the quality of reared fISh in thehatchery are discussed from a practical viewpoint.

Differences between wild
and reared fish_

Numerous studies on differences in quality between wild andreared fish have appeared for salmon and trout (e.g., Phillips
et al. 1957, Vincent 1960, Wood et al. 1960, Green 1964,
Bams 1967, Kobayashi and Ohkuma 1983). Special attention was given to determining meJlsures of quality and to
exercising the fry to improve their survival potential in thecase of anadromous fish. Concerning marine fish, in spiteof their great economic importance, few basic data on biological characteristics of hatchery-raised fish are available.
Table 1 shows the differences in biochemical and morphological aspects of sparid fish. Artificially reared fish havebeen shown in most cases to display a pronounced inferiority to wild fish both in behavior and survival potential. Highlipid content is a biochemical feature of reared fish in general,
as well as red sea bream. It is uncertain whether the inferiority of reared fish has any effect on survival potential following transfer to the sea.
The general explanation for the poor quality of reared fish
is that environmental conditions of reared fish differ largely
from those in the wild. In the hatchery, a high percentage
of fish can survive due to lack of predation, starvation, andlethal environmental changes, in other words, "selection
pressure" (Blaxter 1975). Newly hatched larvae which
would die in the wild are capable of feeding on prey andsurviving under enhanced rearing conditions. The variationin size can be observed even at the egg stage and also in newly
hatched larvae in any species. Morphological differences,117

for Releasing

pagrusmajor
45%,

f - - .-------I

parill1chthys
olivaceus-0

Acanthopagrus
schlegeli

for Cage culture
Crustacea
3%0.

Figure 1
Species composition of artificial propagation for releasing and cage culture, and total number of fry produced in releasing program. (Source: Annual report of artificial releasing of reared marine seeds, Fisheryagency, Jpn. Farm Fish. Assoc.)

Table 1
Biological differences between wild and reared fry in sparid fish
Species

Items*

Wild

RearedSourcePagrus rruljor

Water
Lipid
CarbonHydrogen
NitrogenC/N

78-79%
2-10 mg35-43%
5.2-6.2%
10.0-12.1 %3.4-3.8

82-72%
3-400 mg42-49%
5.9-6.7%
9.5-11.6%
3.7-5.0

Anraku and Azeta (1973)

Response to threat
Abdominal fat content

Sensitive

Weak
HigherTateishi (1974)

Size of fish with complete
stripes

11.5 mm SL

9.0 mm SL

Fukuhara and Kuniyuki (1978)

Total lipids

1.00 - 1.05

Oplegruuhus jasciatus

1.95-2.04

Ohshima et aI. (1983)

Body height, eye diameter,
upper jaw length

Smaller

Matsumiya et aI. (1984)

Muscle freshness

Decreased more
rapidly

Iwamoto and Yamanaka (1986)

23.2-81.3%

Fukusho (1979)

Malformation of stripes

19.8%*Percent wet weight for water content; percent dry weight for others.

118particularly size at early life stage, lead to size hierarchy anddifferences in fish activities (Yamagishi 1964).
Morphological changes in eggs and larvae depend largelyon the nutritional conditions of spawning fish of red sea
bream (Watanabe et al. 1984). To observe the survival curve,
Keitoku et al. (1985) conducted a starvation experiment oflarval red sea bream maintained simultaneously in a largescale tank used for artificial propagation. The starvation experiment indicated the existence of poor-quality larvae whichdied prior to the point of no return (PNR) (Fig. 2), and aclose relationship was found between survival in the starvation test and percent survival of fish at harvest in the hatcheryproduction unit. These findings suggested the source of difference in fish quality is related to the health of broodstock
or developmental stages of newly hatched larvae. In addition, larvae are free from starvation and predation pressurein the rearing tank, which allows non-exercised fish to avoid
various lethal conditions and experience a high survival rate.
Biological characteristics of non-exercised fish become fixed
as the rearing period lengthens, leading to a loss of wildness
and to an inability of the hatchery-reared fish to adjust to
new surroundings after transfer (Azuma 1974, Blaxter 1975).

PNR

80

~ 60

...
>

::)

rn

...
~

...

40

(,,)

Q>

a.

20

o
2

3

4

5

6

7

8

9

10

Days after hatching

Figure 2

Determining fish quality

Survival curves for larval red sea bream in unfed condition.
PNR = point of no return. Redrawn from Keitoku et al. 1985 andFukuhara 1974.)_

Stamina tunnels or swimming performance have been used
to evaluate the quality of planted salmon and trout (e.g.,
Vincent 1960, Green 1964, Bams 1967). As for marine fish,various examinations have been used to determine fish
quality: rheotaxis, resistance to exposure, starvation, low
oxygen concentrations, and narcotization (Kitajima et al.
1980, Ohgami and Suzuki 1983, Keitoku et al. 1985,
Maruyama 1985). An exposure test was employed to compare the activity of reared juveniles in a nutritional experiment. Mortality and recovery time of examined juveniles
usually correlate with nutritional conditions (Kitajima et al.
1978, 1980). Maruyama (1985) compared mortality andrecovery time, following a 2-minute exposure, between conventionally reared fish and semi-wild fish reared in an earthen
pond. One minute after exposure, 80% of the semi-wild fishrecovered with no mortality. On the other hand, less than
25 % of the hatchery-reared fish recovered after 1 minute with
50 % mortality. These observations suggest that an exposure
test is available which may predict the activity of reared fishunder different conditions, and that the differences are causedby different habitat and/or food items previously ingested.
In Ayu fish Plecoglossus altivelis, a freshwater species,
swimming performance is usually employed to assess the
migrant behavior of hatchery-reared fish (Fig. 3). Fish raised
under lotic conditions showed a higher percentage of migrant
behavior than those under lentic conditions. Adjustment towater current of 30-60 cm/sec prior to planting is effective
for this species in increasing upstream movement (Hiroshima
Prefect. Freshwater Fish Cent. 1983).

Conclusions_

It can be reasoned that qualitative differences exist between
reared and wild fish if biotic and abiotic conditions are compared. The causes of differences in both animals are mainly
attributable to differences in feeding and habitat situations.
Hatchery-reared fish are immediately subjected to reduced
food levels and the threat of predation following transplantation. To alleviate various stresses to newly introduced fish,some manipulation (such as exposure to moving water,
predators, and starvation) is required during the course ofrearing or before planting. Fish exposed to predators wereless vulnerable to predation, resulting in decreased fry mortality (Ginetz and Larkin 1976). Henderson (1980) emphasized the necessity of certain durations for transplanted fish:periods of recovery of normal movement, familiarization
with the new habitat, and adjustment of feeding habit. As
already mentioned for Ayu fish, exercise in a water current
is a profitable strategy prior to planting. Swimming exercise increased endurance in trained coho salmon comparedwith control groups, and the effect of exercise was maintained for 2 months (Besner and Smith 1983).
These studies indicate that some manipulations are effective in exercising and ajusting reared fry prior to release in
a new habitat. As for marine fish production, to improve
the quality of reared fish and to increase the survival potential after planting, the inferiority of laboratory-reared fishmust be prevented during rearing (Fig. 4). The concept of
119

II
II
II

II
II

II
II
II

Figure 3
Diagram of apparatus to determine migrant behavior in Ayu fish.

Overcoming of inferiority

Elimino.tion of inferiorit

Figure 4
Concept for evaluating and improving fish quality in artificial propagation and releasing procedures.

Citations

exercise and adjustment is not currently employed in rearing procedures from egg stage to young. Starvation tests of
newly hatched larvae before reaching PNR indicate the possibility of selecting viable larvae for production purposes(Fukuhara 1974, Keitoku et al. 1985). Experimentally, hatchery fish reared in a water current are usually resistant tohandling procedures during transfer.
In Japan, intermediate rearing of marine fish is generally
conducted in net cages before their release. This intermediate
rearing is aimed in most cases at improving the effectivenessof the rearing facility and increasing fish length prior to release. Exercise and exposure to starvation and predation areneeded to improve fish quality in the intermediate rearing
strategy. Quality determinations of reared fish become more
important to the evaluation of artificial recruitment effects
as releasing activities are carried out vigorously for various
marine fishes in the future. In tum, releasing techniques mustbe established to produce planting seeds which meed thebiological characteristics needed for aquaculture ventures.

Anraku, M., and M. Azeta
1973 Difference of body components between artificially reared andnatural sea bream: larva and young. Bull. Seikai Reg. Fish. Res.
Lab. 43:117-131.
Azuma, M.
1974 Planting experiments of hatchery and wild Ayu-fish into streams
and some biological problems of the farming fishery. Jpn. J.
Michurin BioI. 10: 116-122.
Barns, R.A.
1967 Differences in performance of naturally and artificially propagated sockeye salmon migrant fry, as measured with swimming andpredation tests. J. Fish. Res. Board Can. 24:1117-1153.
Besner, M., and L.S. Smith
1983 Modification of swimming mode and stamina in two stocks ofcoho salmon (Oncorhynchus /dsutch) by differing levels oflong-terrn
continuous exercise. Can. J. Fish. Aquat. Sci. 40:933-939.
Blaxter, J.B.S.
1975 Reared and wild fish-how do they compare? In Euro. Symp.
Mar. BioI., 10th Ostend, Belgium, ed. G. Persone and E. Jaspers.
Vol. 1, Mariculture, p. 11-26. Inst. Mar. Sci. Res., Bredene,
Belgium.
120

I

r

_

Nose, T.

Fukuhara, O.

1985 Recent advances in aquaculture in Japan.
261-276.

1974 The influence of initial delay of feeding on survival, growth anddevelopment of the red sea bream larvae, Chrysophrys major Temminck et Shlegel. Bull. Nansei Reg. Fish. Res. Lab. 7:19-29.
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Ohgami, H., and T. Suzuki
1983 Examination of activity determination for larval red sea
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Ohshima, T., S. Wada, and C. Koizurni
1983 Comparison of lipids between cultured and wild sea bream.
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1957 A chemical composition of hatchery and wild brook trout.
Prog. Fish-Cult. 19:19-25.

Fukuhara, 0., and K. Kuniyuki
1978 Morphological development in the wild larvae of Madai, Chrysophrys major, as compared to that in the laboratory-reared larvae.
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Tateishi, M.
1974 On the ecology and results of tagging experiments of red sea
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Fukusho, K.
1979 Studies on fry production of Japanese striped knifejaw Oplegnathus fasciatus, with special reference to feeding ecology and massculture of food organism. Spec. Rep. Nagasaki Prefect. Inst. Fish.
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Vincent, R.E.
1960 Some influence of domestication upon three stocks of brook trout(Salvelinusfontinalis Mitchill). Trans. Am. Fish. Soc. 89:35-52.

Ginetz, R.M., and P.A. Larkin

Watanabe, T., T. Arakawa, C. Kitajima, and S. Fujita

1976 Factors affecting rainbow trout (Salrno gairdnen) predation on
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1984 Effect of nutritional quality of broodstock diets on reproduction of red sea bream. Bull. Jpn. Soc. Sci. Fish. 50:495-501.

Wood, E.M., W.T. Yasutake, J.E. Halver, and S.N. Woodall

Green, D.M.

1960 Chemical and histological studies of wild and hatchery salmon
in fresh water. Trans. Am. Fish. Soc. 89:301-307.

1964 A comparison of stamina of brook trout from wild and domestic
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Yamagishi, H.

Henderson, H.F.

1964 Growth variations of fish.

1980 Behavioral adjustment of fishes to release into a new habitat.
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Hiroshima Prefectureal Freshwater Fish Center
1983 Jumping test for investigating migrant behavior and the past lifeof frys, p. 34. Kawate-cho 23-1, Shoubara, 727-12 Hiroshima [inJpn.].

Iwamoto, M., and H Yamanaka
1986 Remarkable differences in rigor mortis between wild and cultured specimens of red sea bream Pagrus major. Bull. Jpn. Soc.
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Keitoku H., H. Yasue, M. Tanaka, K. Hanaoka, Y. Nakasugi, and
N. Urasaki
1985 Artificial propagation of Sparid fish.
Farm. Fish. Assoc. 4:1-14 [in Jpn.].

Geojournal 10:

Anou. Rep. Hiroshima

Kitajima, C., S. Fujita, F. Ohwa, Y. Yone, and T. Watanabe
1978 Improvement of dietary value for red sea bream larvae of rotifers
Brachionus plicatilis cultured with Baker's yeast Saccharomyces
cerevisiae. Bull. Jpn. Soc. Sci. Fish. 45:469-471.

Kitajima T., T. Arakawa, F. Oowa, S. Fujita, 0 Imada, T. Watanabe,
and Y. Yone
1980 Dietary value for red sea bream larvae of rotifer Brachionus
plieatilis cultured with a new type of yeast. Bull. Jpn. Soc. Sci. Fish.
46:43-46.

Kobayashi, T., and K. Ohkurna
1983 On the device for stamina measurement of salmon fry. ·Sci.
Rep. Hokkaido Salmon Hatchery 37:41-44 [in Jpn.].

Kuronurna, K., and K. Fukusho
1984 Rearing of marine fish larvae in Japan. IDRC-TS47e, Int. Dev.
Res. Cent., Ottawa, Ontario, Canada. 109 p.

Maruyama, K.
1985 Experiment on quality determination of red sea bream fry.
Anou. Rep. Jpn. Farm. Fish. Assoc. Fiscal Year 59: 129-133.
Kaigan-dori 2-2-3, Chuou-ku, Koube 650 Hyougo [in Jpn.].

Matsumiya, Y., H. Kanamaru, M. Oka, and M. Tateishi
1984 Morphometric comparison between artificially-released red sea
bream and Q-age wild fish. Bull. Jpn. Soc. Sci. Fish. 50:1173-1178.

121

BioI. Sci. 16:98-104 [in Jpn.].

Recent Progressin Artificial Propagationof Marine Species forJapanese Sea-farmingand Aquaculture

In the last decade, with changes in social and economic conditions, including the imposition of 2OQ-mile territorial waters
by many countries, the roles of sea-farming and aquaculture
have become more important in the coastal fisheries of Japan.
In this connection, considerable efforts have been directedby governments and individuals to develop techniques of artificial propagation, which are the basis of fish farming andaquaculture. As a result, considerable progress has been
made in this field.
As illustrated in Figure 1, in the 7 years during 1977-84,
larval rearing of various species has steadily increased in
number (unpublished Prefectural and Fishery Agency reports). In 1984 production of juveniles was attained in 32
species of fishes, 15 species of crustaceans, 21 species ofshellfishes, and 9 miscellaneous species. Production has also
increased in total numbers as well (see Figure 2): 3.8 times
for red sea bream Pagrus major, more than 40 times forJapanese flounder Paralichthys olivaceus, about 5 times forblue crab Portunus trituberculatus, and 3.8 times for abalones (Haliotis spp.). The production of Kuruma prawns
Penaeus japonicus and Yesso scallop Patinopecten yessoensis
had already attained high levels by the mid-1970s and increased another 20% by 1984.
Production of juveniles in 1984, the latest year for whichdata are available, is shown in Table 1 by type of utilizationand hatchery facility (Fishery Agency and Japan Sea Farming Assoc. 1986). ReSearch on larval rearing is carried out
by the following facilities which play different roles in
production:
1 National (A) and local (B) governmental facilites mainly
address the basic, practical aspects of technical development.
2 Local governmental (B) hatcheries disseminate resultsof technical developments to fishermen.

AKIRA SUDA
Japan Sea Farming Association
Kanda-Ogawamachi, 2-12, Chiyoda-Ku
Tokyo. Japan- -- ... ----------.
s"c"~Figure 1
Yearly change in number of species in seed production, 1977-84.

123

3 Fishennens' association (C) and private (D) hatcheries
produce seed for industrial operations.

Sc-lIopl08x2
Ku' ..... .,._nl07

Ot~<pOIC"'$

106

...1'

.9'· ///A great number of scallop seeds are produced exclusively
by group-C hatcheries on a commercial basis for restocking
operations and aquaculture. Fingerlings of red sea bream andJapanese flounder and Kuruma prawn seed are produced inmany hatcheries of all classifications and are used in practical and experimental restocking operations as well as inindustrial aquaculture. In aquaculture of these species, artificially produced seeds are now contributing a larger shareof seed stock. Blue crabs are reared mainly by government(groups A and B) hatcheries, thus seed is not directed toaquaculture but to restocking operations of either a morepractical or experimental nature. In the case of the Tiger puffer Fugu rubripes, fingerlings are produced almost solely
for aquaculture. Various technical problems are still unsolvedfor other species, and government (A and B) hatcheries are"" ..................

::~///SCIliop_e.....-~-a-------.'"='~------'----------'---'----'

Figure 2
Yearly change in number of seeds produced, 1977-84.

Table 1
Number (loJ) of seeds produced in 1984.
Type of utilization
SpeciesSea-farming

Type of facilities

Aquaculture

Herring
Striped jack
Yellowtail
Jack mackerel
Striped knifejaw
Japanese seabass
Three-line grunt
Red-spotted grouper
Black sea bream
Red sea breamBlack rockfish
Scorpionfish
Japanese flounderCommon flounder
Tiger puffer

570
39
1,210
257
880
521
811
49
6,307
22,572
717
240
8,483
2,972
757

Kuruma prawn
Kuma prawn
Yoshi prawn
Hanasaki kingcrab
Mad crab
Blue crab

484,684
3,345
35,927426
1,053
38,350117,165

Abalones
Homed turban
Japanese babylon
Ark shell
Pearl oyster
Noble scallop
Baking scallop
Yesso scallop
Clam shell

29,960
367
749
5,370

1,002
5

Sea urchins426
1,777,710
1,241
4,279

197

A

B

416
39
1,210
257

154
1

542
30
219
49
1,225
16,742
150

4,245
717

5,264

2,567

1,622
90,000426
1,053
13,3508,480
23,5682,104893
1,490,093

C

0

196

1,338
551
592

54

30

6,562
23,908
145
240
6,845
2,972
2,073

177
2,446
5

793
8,711

87

4,188

352,146
1,345
33,093

11,7452,000

147,958

306

2,834

23,944316

740

26,572372
745
13,34012,740
1,714
426

1,813

2,397

4
500
5,028

10
5,800
390

893
3,267,803

1,241
70

4,025

324

Group A: National facilites (National Research Institute of Aquaculture and Japan Sea Farming Association)
Group B: Local governmental hatcheriesGroup C: Fishermen's association hatcheriesGroup 0: Private hatcheries

124

Table 2
Efficiencies of rearing techniques represented by survival rate andnumber of seeds per cubic meter at the end of production.

SpeciesSize ofseed(mrn)

Survival
rate

20
20

10
35-40

(%)

REO seABAEAM

Number of
seed

per m

\

•

50

3

•

•
•

Yellowtail
Red sea bream
Three-line gruntBlack rockfish
Japanese flounder
Herring

17

60

30
20
50

60
60
60

500
5,000
2,500
1,690
5,000
3,000

Kuruma prawn
Blue crab
Hanasaki kingcrab

13
Crab stage 1
Crab stage 1

70
25-40
60

18,0006,000-10,000
7,500.... . • • •••••... • .. •
•••
•••
!e

•

•

•

\ ••• C~ •10~

• ••••

•

somm

10

JAPANESE FLOUNDER•
involved in basic studies. For such groups, the developmentof rearing techniques for species not previously cultured isa major responsibility.

Recent views ofrearing techniques

50

•••
•

_
10

Efficiency

•

•
•
•
•
•
•
••
•• •• • ••• • •••

10

Nine selected species from the Japan Sea Farming Association are presented in Table 2 to show the efficiency of rearing techniques, represented by (1) survival rates throughout
the process of larval rearing and (2) number of larvae reared
per cubic meter at the end of the process (Japan Sea Farming Assoc. 1984). Survival rates are more than 30%, exceeding 50 % in many species. More efficient rearing of somespecies has been reported from some of the hatcheries ingroup B. Intensive mass production of juveniles with highsurvival rates is becoming practical for red sea bream,
Japanese flounder, Kuruma prawn, and blue crab in many
Japanese hatcheries, although some problems still remain.

•
50

I·

•
80mm

TOTAL LENGTH

Figure 3
Fluctuation of survival rate (%) at the end of seed production among
hatcheries and years, 1982-84.

raising particular species, including malnutrition of rotifers
and cannibalism of yellowtail. For these problems, answers
have yet to be found,
Another basic problem is that many more fingerlings areneeded to develop restocking operations, because the number
produced by natural recruitment is greater than that of fingerlings released. Also, we have no conclusive evidence of theability of fingerlings to survive in the wild. This ability isessential for the success of restocking operations. The matter
will be observed further in the discussion on restocking of
red sea bream.

Areas needing improvement
One basic problem is that the survival rate of larvae fluctuates widely in every rearing operation even within the samefacility. Moreover, as is shown in Figure 3, survival rates
vary among years and hatcheries (Japan Sea Farming Assoc.
1983, 1984, 1985; unpub!. Prefectural and Fishery Agency
reports). Such fluctuations are due to many uncontrolled
causes such as quality of brood fish, conditions in the rearing
tank:, food quality, occurrence of disease, and cannibalism.
Remarkable difficulties occur with some species for whichmass production of fingerlings is becoming practical. For
example, body deformity with abnormal pigmentation frequently occurs in flounder and flatfishes. Also, severe lossesof larvae occur during the rearing of Kuruma prawn caused
by baculovirus disease. Usually special problems occur in

An example of a
restocking operation_

Currently, restocking operations on some commercial species, e.g., Kuruma prawn, blue crab, scallops, red sea bream,
and flounder, are being undertaken in various areas in Japan.
Among them, the operation on Yesso scallop resulted in aremarkable catch increase from 15 thousand tons in the
125

I
.1

r:f~

1$'

,.t
Figure 4

Figure 5

Number (l03) of fmgerlings of red sea bream released, by prefecture,
1984.

Ratio of number of fmgerlings released to that of catch in number, byprefecture, 1984.

C = R . FIZ

mid-1940s to more than 120 thousand tons in 1984 (Bureauof Statistics 1985). As to other species, generally speaking,the effects of stocking have not yet proVen statistically significant. Still, some local stocks, when combined with favorable
natural conditions and the efforts of people involved, havebeen effectively restocked.
Following is an outline of the red sea bream restocking
operations" as an example for discussion.
1 Before release, fingerlings are kept for a short time ina pen at the location where they will be released to acclimatize
them to the wild environment. Figure 4 illustrates the numberof fingerlings released by each prefecture (Fishery Agency
and Japan Sea Farming Assoc. 1986). To decide the scaleof release, it is important to know whether the amount of
release is large enough compared with that of natural recruitment. To arrange the key to this question, the ratio of thenumber of fingerlings released to th~, number caught locallyis given in Figure 5. When the ratio is less than 1, the amountof release is expected to be less than natural recruitment.

R'IC = R'/(R . FIZ)

If R' IC < 1, then R'IR < FIZ < 1
where R = number of natural recruitment,
R' = number of fingerlings released,
C = number of catch in a given year, including all
age groups,
F = instantaneous rate of fishing mortality, andZ = instantaneous rate of total mortality.

In many cases, the ratio is less than 1 which suggests more
fingerlings are necessary before the beneficial effects of thestocking operation are obvious (Fig. 5) (Bureau of Statistics
1985, Fishery Agency and Japan Sea Farming Assoc. 1986).
2 In Areas 1 and 2 in Figure 5, the ratio is fairly high,especially in Area 1 where the catch actually increased recently by about 20% (""lO tons in weight) (Kanagawa Prefect.
Fish. Exp. Stn. 1986). Here, the catch by sportfishing is126

estimated at 30--35 tons. If the latter estimate is taken into
consideration, the increase in catch should be much more.
In Area 2, surveys of fish markets indicated that about 10%of the catch came from fingerlings released (Hiroshima
Prefect. Fish Exp. Stn. 1985).
3 The quality of fingerlings must he examined. It is
expected that the difference in inherent abilities of fingerlings to survive the wild environment affects the efficiencyof the operation. Recently, attempts have been made to growlarvae of red sea bream in an extensive rearing system ina large outdoor pond without an artificial diet. Some endurance tests on larvae grown in this way suggest that fingerlings reared in extensive culture survive in the wild better
than those reared in intensive culture. This also suggests
we can enhance the survival ability through the manner ofrearing (Japan Sea Farming Assoc. 1985).
4 Cost of fingerlings is also an important factor for a practical operation. In 1984, the cost for group-B hatcheries
ranged between 3 and 50 yen, with a mean value of 13.5
yen, per fish. Preliminary calculations of total expenditures
to restock a fingerling, though still uncertain, suggest thatit costs two to three times and more than the expendituresof rearng alone. The cost of fingerling production, together
with other restocking costs, must be reduced if the operation is to be more cost-effective. Thus, more improvements
in rearing techniques are needed for the healthy developmentof a restocking program.

Citations_Bureau of Statistics
1985 Annual report of statistics on the production of fisheries andaquaculture, 1984. Ministry of Agriculture, Forestry and Fishery.
Fishery Agency and Japan Sea Farming Association
1986 Saibai-Gyogyo Shubyo-Seisan, Nyushu. Horyu Jisseki, 1984,
p. 373. [In Jpn., limited issue; temporary English title: Materials
on the production and release of fingerlings for sea farming, 1984.]
Hiroshima Prefectural Fisheries Experiment Station et al.
1985 Kaiyusei-gyorui Kyodo-horyu-Jikken-chosa Jigyo. Setonaikaiseibu-kaiiki Sogo-hokokusho, p. 123 [in Jpn.].
Japan Sea Farming Association
1983 Nippon-Saibai-Gyogyo-Kyokai Jigyo-nenpo, 1982, p. 369. [InJpn.; temporary English title: Annual technical report of Japan Sea
Farming Association, 1982.J
1984 Nippon-Saibai-Gyogyo-Kyokai Jigyo-nenpo, 1983, p. 296. [InJpn.; temporary English title: Annual technical report of Japan Sea
Farming Association, 1983.]
1985 Nippon-5aibai-Gyogyo-Kyokai Jigyo-nenpo, 1984, p. 374. [InJpn.; temporary English title: Annual technical report of Japan Sea
Farming Association, 1984.]
Kanagawa Prefectural Fisheries Experiment Station et aI.
1985 Kaiyusei-gyorui Kyodo-horyu-Jikken-chosa Jigyo Sogohokokusho, Taiheiyo-naka-ku, Madai-han, p. 51 [in Jpn.].

127