NOAA Technical Report NMFS 69

Environmental Quality
and Aquaculture Systems
Proceedings of the Thirteenth
U.S.-Japan Meeting on Aquaculture,
Mie, Japan,
October 24-25, 1984
Carl J. Sindermann (editor)

u.s. Department of Commerce

October 1988

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 fishmg industry through marketing service
and economic analysis programs, and mortgage insurance and vessel construction subsidies. It collects, analyzes, and publishes statistics L'n 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"Cireular." 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 interest 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.
34. Additions to a revision of the shark genus Careharhinus; Synonymy of Aprionodon and Hypoprion, and description of a new species of Careharhinus (Carcharhinidae),by J. A. F. Garrick. November 1985,26 p.
35. Synoptic review of the literature on the Southern oyster drill Thais haemastoma
floridona, by Philip A. Butler. November 1985, 9 p.
36. An egg production method for estimating spawning biomass of pelagic fish;
Application to the northern anchovy, Engraulis mordax, by Reuben Lasker (editor).
December 1985, 99 p.
37. A histopathologic evaluation of gross lesions excised from commercially important North Atlantic marine fishes, by Robert A. Murchelano, Linda DespresPatanjo, and John Ziskowski. March 1986, 14 p.

50. Preparation of acetate peels of valves from the ocean quahog, Aretiea islandica,
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.

38. Fishery atlas of the northwestern Hawaiian Islands, by Richard N. Uchida andJames H. Uchiyama (editors). September 1986, 142 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.

39. Survey of fish protective facilities at water withdrawal sites on the Snake andColumbia Rivers, by George A. Swan, Tommy G. Withrow, and Donn L. Park. April
1986, 34 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.

40. Potential impact of ocean thermal energy conversion (OTEC) on fisheries, by
Edward P. Myers, Donald E. Hoss, Walter M. Matsumoto, David S. Peters, Michael
P. Seki, Richard N. Uchida, John D. Ditmars, and Robert A. Paddock. June 1986,
33 p.

56. Some aspects of the ecology of the leatherback turtle Dermoehelys eoriaeea at
Laguna Jolova, Costa Rica, by Harold F. Hirth and Larry H. Ogren. July 1987, 14 p,

41. A stationary visual census technique for quantitatively assessing community structure of coral reef fishes, by James A. Bohnsack and Scott P. Bannerol. July 1986, 15 p.
42. Effects of temperature on the biology of the northern shrimp, Pandalus borealis,in the Gulf of Maine, by Spencer Apollonio, David K. Stevenson, and Earl E. Dunton,
Jr. September 1986, 22 p.
43. Environment and resources of seamounts in the North Pacific, by Richard N.
Uchida, Sigeiti Hayasi, and George W. BoehJert (editors). September 1986, 105 p.
44. Synopsis of biological data on the porgies, Calamus aretifrons and C. proridens(Pisces; Sparidae), by George H. Darcy. September 1986, 19 p.
45. Meristic variation in Sebastes (Scorpaenidae), with an analysis of character
association and bilateral pattern and their significance in species separation, by Lochai Chen. September 1986, 17 p.
46. Distribution and relative abundance of pelagic nonsalmonid nekton off Oregon
and Washington 1979-84, by Richard D. Brodeur and William G. Pearcy. De~ember
1986, 85 p.
47. Reproduction, maturation, and seed production of cultured species; Proceedingsof the twelfth U.S.-Japan meeting on aquaculture, Baton Rouge, Louisiana, October
25-29, 1983, by Carl J. Sindermann (editor). February 1987, 73 p.
48. Widow rockfish; Proceedings of a workshop, Tiburon, California, December
11-12,1980, by William H. Lenarz and Donald R. Gunderson (editors). January 1987,
57 p.
49. Reproduction, movements, and population dynamics of the southern kingfish,
Mentieirrhus amerieanus, in the northwestern Gulf of Mexico, by Stephen M. Harding
and Mark E. Chittenden, Jr. March 1987, 21 p.

57. Food habits and dietary variability of pelagic nekton off Oregon and Washington,
1979-1984, by Richard D. Brodeur, Harriet V. Lorz, and William G. Pearcy. July
1987,32 p.
58. Stock assessment of the Gulf menhaden, Brevoortia potronus, 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 menhaden, Brevoortia 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 for starch gel electrophoresis; A method for the detection of genetic varia·
tion, 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, 1972-85, byCynthia S. Martin, Shelley E. Arenas, Jacki A, Guffey, and Joni M. Packard.
December 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. mustrated 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.

NOAA Technical Report NMFS 69

Environmental Quality
and Aquaculture Systems
Proceedings of the Thirteenth
U.S.-Japan Meeting on Aquaculture,
Mie, Japan,
October 24-25, 1984

Carl J. Sindermann (editor)
Panel Chairmen:
Conrad Mahnken, United States
Kaoru Tatara, Japan
Under the U.S.-Japan Cooperative Programin Natural Resources (UJNR)

October 1988

U.S. DEPARTMENT OF COMMERCE

c. William Verity, Jr., Secretary
National Oceanic and Atmospheric Administration
William E. Evans, Under Secretary for Oceans and Atmosphere

National Marine Fisheries Service
James Brennan, Assistant Administrator for Fisheries

PREFACE_

The United States and Japanese counterpart panels on aquaculture were formed in 1969 under the United StatesJapan Cooperative Program in Natural Resources (UJNR). The panels currently include specialists drawn from thefederal departments most concerned with 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 States-Japan 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 poUution, 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 tecbnical specialists; exchanges of
information, data, and research findings; annual meetings of the panels, 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
Kaoru Tatara - 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 advenising or sales promotion which would
indicate or imply that N~FS 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.

11

Contents
Chiba, Kenji

Relationship between fish culture methods and pondwater quality in freshwater fish culture 1
Fukusho, Kunihiko, and Chikara Kitajima

Environmental management of larval rearing of marine fishes-A short history of research
to prevent lordosis in red sea bream, Pagrus major 9
Funakoshi, Shoji, Tohru Suzuki, and Koji Wada
Salinity tolerances of marine bivalves 15
Furukawa, Astushi, Hiroshi Fukatani, and Shuji Tsuchida
Temperature preference of immature horse mackerel, Trachurus japonicus, in a verticaltemperature gradient 19
Nakanishi, Takashi

Effects of environment on seedlings of king crab, Paralithodes camtschaticus 25
Noma, Toshifumi

Some methods of water-flow control for mariculture 37
Ohwada, Kouichi, and Haruhiko Uemoto

Environmental conditions in pearl oyster culture grounds in Japan 45iii

Relationship between fishculture methods andpondwater quality infreshwater fish culture
KENJI CHIBA
Fisheries Laboratory Faculty of Agriculture
University of Tokyo Bentenjima, Hamana
Shizuoka, 431-02 Japan

Freshwater fish, such as common carp, eel, rainbow trout and ayu,
are cultured using various methods. Based on the manner of oxygen supply and waste substance removal, these methods can bedivided into three groups: stagnant-water culture, running-water
culture, and recirculation-system culture.
The stocking density in ponds is variable depending upon theculture method. Each culture method has its own oxygen-supply
capacity, and this capacity limits the total amount of fish to be
stocked in each unit. Generally, the running-water culture method
allows an extremely high stocking density, whereas stocking density is lowest in the stagnant-water culture method. On the other
hand, the necessary water volume for each kilogram of fish weightgain is extremely high in running-water culture, and is lowest in
the recirculation-system culture. In other words, the efficiency ofwater utilization is best in the recirculation-system culture and lowest
in the running-water culture.
As each fish-culture method has its own means of oxygen supply
and waste removal, the pattern of water-quality fluctuation is quite
simple to understand in running-water ponds but is complicated instagnant-water ponds. Eel culture in greenhouse ponds is a method
recently developed in Japan. Although it had originally been developed from stagnant-water culture methods, the techniques employedfor oxygen supply and waste removal in this method are different
from those of the stagnant-water culture method. Atmospheric
oxygen is dissolved mechanically by water wheels, and waste substances are removed by discharging water frequently. Water-quality
fluctuations in greenhouse ponds follow a less complicated dynamic
sequence than in stagnant-water ponds. In this method, in whicheels are stocked at high density, extraordinarily high concentrationsof NH4 -N, N02 -N, P04 -P and organic substances are always
observed in pondwater. Under such water-quality conditions, eels
still grow very rapidly.
Generally, in each culture method about 20 % of the nitrogen
supplied with feeds is converted to fish body substance, and therest is transferred to soluble and particulate substances released into
the pondwater and sediments. When fish are stocked at a high density, a large amount of feed is offered daily. Accordingly, those
substances accumulate to a high level in the ponds. Especially inponds without water exchange or with a small inflow rate, thesesubstances will accumulate continuously to remarkable levels. Eel
culture in greenhouse ponds is a typical example of such situations.
The fact that under such water-quality conditions eels still can beproduced on a commercial scale gives several hints about waterquality management strategies in fish-culture ponds, but these arestill insufficient for proper adjustment of operational strategies.
An urgent need exists, therefore, to clarify the growth-limiting
factors under sufficient dissolved-oxygen conditions. Further, it isalso necessary to improve techniques for treating discharged pondwaters and sediments which are highly loaded with inorganic andorganic substances, in order to prevent the pollution of rivers, lakes,
and the sea, to which aquaculture units release their wastewater.
It seems reasonable to determine the relationship between the fishculture methods employed and the pondwater quality achieved, for
identification of problems concerned with the effective utilizationof water resources in fish production. In this paper, water-quality
fluctuations observed under various culture methods and the resulting growth-limiting factors are examined.

Fish-culture method andstocking density

Table 1_Fish density using various carp culture methods.

The stocking densities per meter2 and meter 3 employed undervarious culture methods are shown in Table 1, along with water
volumes required to produce 1 kg of fish under various methods.
The culture of carp is used here as an example to demonstrate operational conditions (Nakamura 1963, Chiba 1965a). The ratio between
harvesting and stocking differs little among the methods described,
and it is assumed that growth rates necessary for carp to reachmarket size were not dependent on culture methods. At harvest,
the fish weight per meter2 ranged between 0.1 and 0.5 kg in theirrigation pond, between 60 and 190 kg in the running-water pond,
between 7 and 68 kg in the floating cage, and between 11 and 33
kg in the recirculation system. The harvest in the running-water
pond was about 100 to 400 times greater than in the irrigation pond.
On the other hand, the water volume needed to produce 1 kg ofcarp was estimated at 4-20 m3 in the irrigation pond, 2.5-5.0 m3
in the artificial fish pond, and 1,000-2,000 m3 in the running-water
pond. Thus, harvests from a surface area of 1 m2 in running-water
ponds were extremely high, but the water volume required to produce 1 kg of carp was much higher than in stagnant-water ponds.
In the recirculation system, the stocking density was second highest,
close to that in running-water ponds, but the water volume needed
to harvest 1 kg carp was estimated at only 0.5-1.3 m3 . Thesefigures are remarkably small in comparison with those for runningwater ponds.
The same relationships between these culture methods were also
observed in ayu and eel culture. In the case of ayu, the harvest froma I-m 2 pond area and the water volume required to produce 1 kg
weight were 10-20 kg and 31.4-145.6 m3 , respectively, in ordinary
running-water ponds, whereas the necessary water volume was only
2.68-6.93 m3 in the recirculation system (Tokushima Pref. 1978).
In the case of eel culture in stagnant-water ponds or with a small
water supply, the stocking density was 0.6-4.5 kg/m2 and thenecessary water volume to produce 1 kg of weight was 24-193 m3 .
In the recirculation system, the values were 28 kg/m2 and 1.2-1.5
m3, respectively (Mie Pref. 1978). In some specific cases, thestocking density in a recirculation system was as high as 50.6
kg/m2 (Tanaka 1976).
The main differences between culturing methods lie in the principle of oxygen supply and the removal of waste from the ponds.
In running-water ponds, oxygen is supplied with the inflowing water
which also dilutes the waste substances produced by fish metabolism and carries them out with outflowing water. In the stagnantwater ponds, oxygen is usually supplied through photosynthesis by
the phytoplankton populations, utilizing the nutrients supplied
through waste products of fish which have been decomposed bybacteria. In the recirculation system, oxygen is mechanically supplied by waterwheels or blowers and airstones. The waste products
are decomposed and oxidized by bacteria in the filter bed. It was
thus concluded that the differences are caused by the differencesin oxygen supply and waste removal systems.

Fish-culture method andwater quality(kg/m 3)

Water volume
required for
1 kg production(mJ)

0.005-0.08

12-2000.05-0.25

4-20

HarvestCulture method

Fish pond(kg/m 2 )Culture in
Irrigation pond * 0.01-0.15
stagnant water Irrigation pond
0.1-0.5(with feeding)

Culture in
recirculation

Culture pond

0.4-0.8

0.2-0.4

2.5-5.0

Recirculationsystem pond

11-33

4-15

0.5-1.3

Floating cage

7-60

3.5-34

Running-waterpond

60-19030-95systemCulture inrunning water

1,000-2,000*no feeding, only fertilizing the pond.

some is scattered into the water and deposited afterwards on thebottom. After digestion, feces are discharged which also settle on
the bottom. At the same time, NH4 + and urine are excreted
through gills and kidney. Food and feces in the organic bottom
sediments are decomposed by bacteria to inorganic substances. In
the pondwater , phytoplankton starts to propagate utilizing these
inorganic substances as nutrients. Oxygen is produced and CO2 isutilized by phytoplankton in the process of photosynthesis. In contrast, dissolved oxygen is utilized and CO2 is excreted by fish.
Also, oxygen is consumed by bacteria and other organisms in pondwater and bottom mud.
These substances in the pondwater are diluted by inflowing waterand carried away through the outlet. Total amounts of organic
substances decomposed in fish ponds differ, depending upon thecapacity of bacteria to decompose organic matter and the amountof total organic substances in ponds. The decomposition of organic
matter by bacteria is not always at constant speed; the differences
are dependent on the activity of the bacteria and the compositionof the organic matter. The utilization rates of inorganic substancesby phytoplankton, and the rates of oxygen consumption and excretion by fish also differ with their activity patterns, which also dependon the day and night cycle as well as other associated variationsof environmental factors such as temperature. Accordingly, thesupply and consumption of inorganic substances in the pond differ
also with the size of phytoplankton and fish populations.
When the ponds are arranged in sequence along a small stream,
it is observed that dissolved oxygen and pH values decrease whereas
NH 4 -N, N0 2-N, P04 -P, alkalinity, and chemical oxygen demand
increase in downstream ponds, receiving the water coming fromupstream ponds (Chiba 1965b, Shirahata 1964).
In recirculation system ponds, where the activity of bacteria inthe biofilter is sufficient to cope with the load, it is observed that
NH 4-N increases markedly at the beginning of the culture period
and then decreases sharply. In contrast to the decreasing NH4 -N
concentration, N02 -N level increases remarkably as a result of
nitrification. Later on, the N0 2-N level decreases but at a slower
rate. Thereafter, NH4 -N and N0 2-N are stabilized and maintained
at nearly constant levels. However, NOr N increases gradually,and simultaneously pH values and alkalinity decreases. At the sametime, total organic carbon and chemical oxygen demand also increase gradually (Kawai et al. 1964).

_

The cycle of organic and inorganic substances which occur in fish
ponds is shown schematically in Figure 1. Food is supplied daily
to fish in the ponds. In other words, organic substances are added
to the pond water everyday. Almost all food is taken by fish but

2Fe ed-----Inf Iow(oxygen supply
and dilutionof inorganic

Outf low(carry ing away
organic andinorganic matter)and org ani cmalle r)(,,:scattered
feed

J

.

set t lin g( ,\..

,norGanlc
sUbtance

1

decomposit i on

sedimentbottom mudj

sed imentb i at i c
f i Iterba c te ria----_.......
(recirculat ion
system)bacteria

Figure 1
Cycling of organic and inorganic substances in fish-culture pond.

vival rate of the glass eel in greenhouse ponds is quite high. Furthermore, the growth rate is also remarkably high, and the culture
period from glass eel to market size is substantially shortened. For
these reasons the method was adopted by nearly all the eel culturists
in Japan, usually in combination with the conventional method,
depending on season.
The pond area under greenhouse culture ranges from 150 to 1,000
mZ , and water depth varies between 0.6 and 0.8 m. These ponds
are constructed in greenhouses which are covered by vinyl chloride
sheets. Small ponds are used for glass eel culture, and larger ponds
are used to culture the fish to market size. For heating, long pipes
connected to a boiler are laid in the ponds. Pondwater is heatedwith steam or warm water which flows through the pipes. Water
wheels are also provided for the purpose of supplying oxygen andremoving sediment. These wheels produce a rapid current, which
forces feces and food remains to be transported to the center ofthe ponds, where they can be drained periodically. One-third to
one-fifth of the pondwater is drained daily with the sediment througha system located at the center of the pond bottom. Except for theremoval of sediments, there is no other special device employed
for water treatment. Usually, phytoplankton does not propagate inthese ponds. Water temperature is regulated at the desired level
ranging between 20 and 32°C. The stocking density is about 6-15
kg/m Z , which is much higher than that used in conventional
stagnant-water culture. The quality of well water and pondwaterin greenhouses of fish farms of the Aichi Prefecture is shown in
Table 2 (Chiba 1980). Dissolved oxygen levels were rather low
in these ponds and were usually below the saturation level, ranging from 40 to 90% saturation. In a few cases phytoplankton populations thrived, causing oxygen supersaturation. Concentrations of
NH 4 -N, NOz-N, and P0 4 -P were also extremely high. Thesewater-quality conditions have not been previously observed in theconventional eel culture ponds.
In these greenhouse ponds, however, eels lost their appetite only
when the dissolved oxygen levels were very low. On the other hand,
it is surprising to note that at remarkably high levels of NH4 -N,
NOz-N, or P0 4 -P, eels never showed reduced appetite as long as
dissolved oxygen was maintained at high levels. Thus, a decreasein oxygen concentration was more harmful to fish than an increase

In the stagnant-water ponds, a very low water flow rate is seldom
applied. Therefore, dissolved and particulate matter are not diluted
continuously. Changes in water quality are mainly caused by theactivities of phytoplankton, bacteria, and fish metabolism. Water
quality changes are expressed in complicated patterns over long
periods, reflecting the dynamics of all the influencing factors (Hirano
1976).
In addition to the long-term water quality changes, different patterns of diurnal water-quality fluctuations are observed in all threeculture methods. In running-water ponds, clear diurnal changes inwater quality are usually observed. With the commencement offeeding, dissolved oxygen and pH values decrease while NH 4 -N
and chemical oxygen demand increase. After completion of feeding
the concentrations of these parameters gradually return to their
original values (Shizuoka Prefect. 1978). In recirculation ponds,
the pattern of diurnal fluctuation in water quality is similar to thatof running-water ponds (Tanaka 1976). In stagnant-water ponds,
clear diurnal fluctuations in water quality are also observed. During daytime, the dissolved oxygen level increases through photosynthetic activity of phytoplankton and reaches its highest level in theafternoon. At night the dissolved oxygen level decreases becauseof respiration of organisms. If the phytoplankton dies or if the dominant species population is reduced and overturns to other species,
the water quality of the pondwater changes suddenly. Usually,
dissolved oxygen decreases while NH 4 -N, NOz-N, and P04-P increase remarkably. In these cases fish lose their appetite or begin
surfacing and sometimes die due to oxygen depletion. Thus, thepatterns of water-quality fluctuations in fish ponds over a 24-hour
period and over a long-term period are varied, depending on theculture method. The manner of oxygen supply to pondwater andwaste removal from it may result in different patterns of waterquality fluctuations.

A new method for eel culture_

Recently, a new method for eel culture was developed by eel culturists in Japan. In this method eels are cultured in heated water
ponds in greenhouses. Compared with former methods, the sur-3

Table 2
Water quality of wellwater and pondwater (greenhouse) of fish farms at Aichi Prefecture.
Wellwater source
Item
Water temperature
pH
DO
NH.-N
NOrN
N0 3 -N
PO.-P
COD
COD
Alkalinity
Ca
Mg
Fe
So
CI
Na
K

(0C)

(%)

ppm
ppm
ppm
ppm
ppm
ppm'
(mg/L)
ppm
ppm
ppm
ppm
ppm
ppm
ppm

Pondwater source

Max.

Min.

Mean

Max.

Min.

Mean

21.8
7.4
61.4
2.750
0.080
8.40
0.132
0.54

17.1
6.3
18.8

19.40
7.01
39.43
1.44500.01414.701
0.0811
0.066

3.750
630
210
6.56
314
3082
970
22.0

0.682
61
43
0.04
19
228
65
6.5

27.5
7.07
156.7
26.400
6.000
24.00
2.575
7.48
3.92
3.364
452
222
0.40
274
2340

20.0
7.1
26.1
0.080
0.020
5.60
0.150
1.34
0.65
0.682
199
18
0.10
18
190

25.49
7.37
72.04
6.30501.240011.26
0.87676.300
2.101
1.3689
183.9
106.5
0.203
106.9
1093.0

ND
ND
0.94

ND
0

1.6716
~68.1

139.9
1.556
163.9
1678.0444.4
14.90

COD = chemical oxygen demand.
DO = dissolved oxygen.
'Sample was filtered by 0.1-1' filter.

of NH 4-N, N02-N, and P04 -P. It is important to maintain a highoxygen concentration at all times while using this culture method.
Examples of production conditions and results of eel culture inheated greenhouse water ponds are shown in Table 3 (Chiba 1980).
Fish grown to table size are usually harvested intermittently, andyoung fish are restocked or transferred between ponds several times
during the culture period. Therefore, it is very difficult to correctly evaluate the production results of fish culture. In gener11, thefeed conversion efficiency can serve as a reasonable indicator ofsystem performance under practical culture conditions. Feed conversion efficiency is calculated as follows: weight gain multipliedby 100 and divided by amount of food given. In general, the average feed conversion efficiency in conventional stagnant-water cultureis estimated to be about 60-70 %. As the figures obtained in ,greenhouse ponds surveyed ranged between 58.7 and 71.4 %. results inthese ponds were not different from those in conventional stagnantwater ponds. Therefore, it seems reasonable to assume that the extremely high concentrations of several water quality factors in greenhouse ponds might not have appreciably influenced feeding or
growth of eels.
However, for further development of this culture method, it isnecessary to clarify the effect of the most important water quality
factors. not only on fish appetite and growth but also on the physiological condition of the fish. Also, effective removal of sediment
seems to be an important technique in pond management using thisculture method. Therefore, the effect of sediment removal on water
quality. fish growth, and appetite should be studied in detail.

Growth-limiting factors

Table 3
Examples of results of eel culture in heated-water pond (greenhouse).
Fish pond

2)(mPond area(0C)
Water temperature
Culturing period 1977-78(calendar month)
Amount of fish stocked (kg)
(initial)(kg)
Amount of fish

0- I'

0-2

KA

F

297
21
10/28
316
670

396
24
10127
6/23
1,570

496
26
10118
1110
2,000

264
24
11/2
6/21
2,625

454

2,100

0

0

1,124

3,670

2,000

2,625

restocked

Total amount of fishstockedInitial stocking density
Harvest of marketable
sized fishes
Fish left in ponds"
Dead fishes
Weight increase
Amount of feeding
Feed efficiency'"(kg)(kg/m 2 )

(kg)
(kg)
(kg)
(kg)
(kg)
(%)

2.26
3.96
4.33
9.94
0
5,942
2,985
2,547
1,300
43
219
627
35.0

1,860
110
4,242
7,222
58.7

828

2,970

1.813
2,540
71.4

2.829
4,700
61.5

'Seedling culture of eel.
"Fishes too small to be harvested.
"'Feed efficiency was estimated from 35 to 71.4 %, no different from those ofordina.-y cultured method.

NH 4 -N, N0 2-N, and N0 3 -N have been reported as limiting factors for fish growth. Their effective concentration ranges are shownin Table 4.
Growth rate, feeding rate, and feed conversion efficiency in manyfish species decreases with a decrease of dissolved oxygen. These
effects were found to occur in common carp when the oxygen concentration decreases to values less than 3 mL/L (20-23°C. or 50%
of air saturation) (Chiba 1965c), for coho salmon at less than 4 ppm_

There are many reports on the effects of organic and inorganic
substances on aquatic animals; however, most are from the standpoint of pollution problems. Only a few studies have tried to clarify
the effects of various water-quality parameters on fish appetite andgrowth. Dissolved oxygen. waste products (Kawamoto 1957),
4

Table 4
Toxic factors affecting aquatic animal life.

Dissolved oxygen

Fish

Critical value

Observation

Authorcommon carp

50%
45%
49%
32 - 43%
54%

Decrease in
growth rate
feeding rate
feed conversion efficiency

Chiba 1965c
Herrmann et al. 1962
Stewart et al. 1967
Adelman and Smith 1970
Yamagata et al. 1983

coho salmon
largemouth bass
morthero pike
eel
NH.-N

NOz-N

N0 3-Neel

20 ppm(NH 3 -N 0.067-0.124 ppm)

Decrease in growth rate

Yamagata and Niwa 1982

ayu-fish5 ppm(NH 3 -N 0.13 ppm)

Decrease in growth rate

Tokushima Pref. 1977

channel catfish

30 ppm(NH 3 -N 0.58-7.48 ppm)

Stop feeding

Knepp and Arkin 1973

rainbow trout

0.15 ppm

Mortality 58% within 48 hr
methemoglobinemia

Smith and Williams 1974

rainbow trout

0.55 ppm

Mortality 40% within 24 hrmethemoglobinemia

Smith and Williams 1974

chinook salmon

5.0 ppm

Mortality 100% in 7 days

Westin 1974eel

30 ppm30 ppmDecrease in growth ratemethemoglobinemia

Yamagata and Niwa 1979
Amano et al. 1981

chinook salmon

4,000 ppm in freshwater
4,800 ppm in seawater

Mortality 100% in 7 days

Westin 1974

rainbow trotit

4,000 ppm in freshwater
4,700 ppm in seawater(Westin 1974). When eels were kept in water at a 20-ppm concentration of NOz-N, all fish developed methemoglobinemia (Amanoet al. 1981). Regarding nitrate, it was reported that chinook salmon
died within 7 days at a concentration of about 4,000-4,800 ppm
NOrN in seawater and freshwater, and rainbow trout died at aconcentration of about 4.000-4,700 ppm N0 3-N (Westin 1974).
Besides the water-quality parameters mentioned above, there areseveral other growth-limiting factors, such as stocking density, competition for food and space, cannibalism, size hierarchy, light conditIOns, and water temperature. However, some of these factors
can be controlled artificially. Sometimes it is observed that eventhough the concentrations of these water-quality parameters arewithin the favorable range. fish lose appetite. This often occurs instagnant-water eel culture ponds. There might be other unknown
factors affecting fish growth and appetite. For the development ofadequate water-quality management in fish culture ponds, much
effort is needed in the future to find out those unknown factors.

(20°C, 45%) (Herrmann et al. 1962), for largemouth bass at lessthan 4 ppm (26°C, 49%) (Stewart et al. 1967), for northern pikeat less than 3-4 ppm (18.7°C, 32-43%) (Adelman and Smith 1970).
and for eel at less than 4.5 ppm (25°C, 54%) (Yamagata et al. 1983).
Itazawa (1971) reported that low ambient dissolved oxygen can cause
a decrease in the oxygen level of arterial blood, starting at 63 %saturation in rainbow trout, 50% saturation in carp, and 31 % saturation in eels. Such dissolved oxygen levels were almost identicalwith those that reduced growth rates in rainbow trout, carp, andeels. It was assumed that fish failed to acquire a satisfactory amountof oxygen from the ambient water to meet their requirements. This
caused poor appetite and a decrease in growth rate.
There are many reports of toxicity of ammonia to aquatic animallife (EIFAC 1973). It is generally believed that un-ionized ammonia
is toxic and the toxicity of total ammonia changes remarkably with
pH and temperature, because of an increase in the un-ionized fraction. However, there are few reports on the effect of lin-ionizedammonia on fish growth. Yamagata and Niwa (1982) rep0l1ed thata decrease in growth rate was observed in eels at 20-40 ppm
NH 4 -N (25°C, pH 6.6-6.7). Based on water temperature and pH
value, the un-ionized ammonia fraction of this total ammonia concentration was calculated to be 0.067-0.121 ppm as NH 3-N. For
ayu, a decrease in growth rate was observed at 5 ppm NH4 -N(25°C, pH 7.6-7.8), resulting in an un-ionized ammonia concentration of 0.13 ppm as NH 3-N (Tokushima Prefect. 1977). For
channel catfish, feeding stopped at 27.3-32.0 ppm NH 4 ,N
(21.l-22.8°C, pH 7.7-8.8) which resulted in NH 3-N values of
0.58-7.48 ppm (Knepp and Arkin 1973).
Concerning nitrite, rainbow trout developed methemoglobinemia
at concentrations below 0.15 and 0.55 ppm NOz-N, and mortalityof 58% and 40% occurred after 48 hours and 24 hours, respectively (Smith and Williams 1974). It was also reported that chinook
salmon died in 7 days at concentrations of NOz-N of 5.0 ppm

Cycles of nitrogen, carbon, andphosphorus in fish ponds_

The elements in feeds, such as nitrogen, carbon, and phosphorus,
are recycled in ponds by the processes of decomposition and utilization, through activities of bacteria and phytoplankton. However,studies on the cycles of these elements in fish culture ponds are
scarce. Experimental work was carried out by the present author
to clarify the cycles of nitrogen, carbon, and phosphorus in eel
ponds. It was found that about 14-25 % of total nitrogen containedin feeds was converted by the fish (Table 5) (Chiba 1983). The
percentages of crude protein contained in whole fish and in commercial feed used in this experiment were both about 50% on a
dry weight basis. Eel culturists generally believe that the conver5

Table 5
Increment of nitrogen, carbon, and phosphorus in each item (gr) and percentages (in parentheses) of those in given feed.
Tank P - 2

Tank P - I

Tank P - 3----------

Item

N

C

N

P

C

P

N

C

P

183
(100)

489
(100)

2,596
(100)

144
(100)

----

Food given

1,375
(100)

6~4

7,300
(100)

404
(I 00)

(IOOI

3,315
(100)

Eel

304
(20.1)

1,562(21.4)

80(19.8)

158(25.3)

780(23.5)

36(19.7)

70(14.3)

344(13.3)

16(11.1)

Sediment

107
(7.8)

670
(9.2)

200
(49.5)

81(13.0)

542( 16.4)87(47.5)

49(10.0)

319(12.3)

57(39.6)

Particulate

92
(6.7)

595
(8.2)

22
(5.3)

188
(30.1)

986(29.7)

9(4.9)

60( 12.3)376(14.5)

12(8.6)

Soluble207(15.1)

312
(4.3)

12
(2.9)

159
(25.5.'

~81

e8.5)

10
(5.5)

140
(28.6)

168
(6.5)

6
(4.1)

710
(51.6)

3,139(43.0)

314(77.6)

586(93.9)

2,589(78.1)

142(77.7)

319(65.2)

1,207(46.5)

91(63.4)

Total

Conclusions

sion efficiency of commercial feeds is between 60 and 70 %.
Therefore, when these values are calculated on a dry weight basis,
20 to 25% of the nitrogen can be converted to fish body from feeds.
The figures obtained from this experiment were nearly identicalto those of eel farmers. Therefore, 75-86% of the nitrogen is transformed to other forms such as soluble substances, particulate suspended matter, and organic sediments. The percentages of nitrogen
which were converted from feed to soluble substances ranged
between 15 and 29 %, between 7 and 30 % to particulate matter,and between 8 and 10% to sediments. As for carbon and phosphorus,
similar results were obtained. Only 13-24% of total carbon and11-20% of phosphorus in the given feeds were converted to fish,
but the major part of these elements was transferred to soluble andparticulate matter, and to bottom sediment.
In running-water ponds, the soluble and particulate matter andorganic sediments are carried away by the outflowing water. In
stagnant-water ponds and recirculation-system ponds, they accumulate in the pondwater, at the pond bottom, and/or in the filter bed.
When fish are stocked at high density, the accumulation rate of thesesubstances will be extremely accelerated.
It can be concluded from these results that only 20-25 % of elements such as nitrogen, carbon, and phosphorus in feeds supplied
to fish were converted into fish body, and the rest was not utilized,
but was accumulated in the ponds. These figures, however, wereobtained from three experiments lasting less than one month. The
conversion figures from feed to fish are believed to be nearly constant over a wide range of fish sizes and also independent of theexperimental period, since feed-conversion efficiency is usually at
the same level. However, the other figures, such as the percentages transferred from feeds to soluble fractions or to particulate
suspended solids and to sediments, can vary substantially depending on the experimental period. These figures can also be influenced
by bacterial activity, fish density, amount of daily feed offered,and fish culture methods employed.
In order to improve existing mthods and to develop new waterquality management strategies for eel pond culture in the future,
further detailed studies are needed on nutrient budgets and element
cycling in the ponds.

_

In order to increase fish-pond production, a number of management efforts must be made to increase stocking density in all fishculture methods practiced today. When the stocking density is
increased, dissolved oxygen level decreases, whereas concentrations of NH4 -N, NOz-N, and organic substances increase and thevalue of chemical oxygen demand elevates. To counteract dissolved
oxygen depletion. water wheels or other aeration systems withblowers must be used to accelerate the transfer of oxygen from theatmosphere. However, against the accumulation of NH4 -N,
NOrN, and organic substances and the elevation of the chemicaloxygen-demand value, no particular countermeasures are presently undertaken, except dilution through the introduction of freshwater. Special attention should be paid to the pollution load andsubsequent water quality deterioration in greenhouse ponds which
are highly loaded with inorganic and organic substances. However,the fact that eels still can be produced on a commercial scale undersuch water-quality conditions provides several suggestions for waterquality management in these fish ponds. On one hand, eels may
be relatively tolerant to water that contains appreciable concentrations of NH 4 -N, NOz-N. and organic substances. However, inorder to maximize production, it will be necessary to clarify theimportance of factors that affect feeding and growth of all fish
species cultured, when oxygen concentrations are kept above criticallevels.
In conclusion, further studies as described below are necessary
to improve pondwater-quality management in order to effectively
utilize water in fish culture:
1. Improvement of methods for effective oxygen transfer into
water;
2. Clarification of factors which have negative effects on fish
production under sufficient oxygen conditions, including theircritical values for normal growth and feeding;
3. Development of treatment procedures for culture effluents
which contain highly enriched organic matter, in order to avoid
water pollution in rivers, lakes, and the sea.

6

Citations_

Westin, D.T.
1974. Nitrate and nitrite toxicity to salmonid fishes. Prog. Fish Cull. 36:86-89.
Yamagata, Y., and M. Niwa.
1979. The toxicity of nitrite to eel. Aquiculture (Sendai) 27:5-11 (in Jpn.). See
Suisan Zoshoku (Fish. Cull.).
1982. Acute and chronic toxicity of ammonia to eel Anguilla japonica. Bull.
Jpn. Soc. Sci. Fish. 48:171-176.
Yamagata, Y., S. Oonaka, M. Harada, and M. Niwa.
1983. Influence of concentration of dissolved oxygen on the growth of Japaneseeel Anguilla japonica. Bull. Jpn. Soc. Sci. Fish. 49: 1335-1339.

Adelman, L.R .• and L.L. Smith.
1970. Effect of oxygen on growth and food conversion efficiency of northernpike. Prog. Fish Cull. 32:93-96.
Amano, H., T. Miyazaki, M. Ichikawa, M. Niwa, and S.S. Kubota.
1981. Occurrence of nitrite-induced methemoglobinemia in cultured eels. Bull.
Jpn. Soc. Sci. Fish. 47:823.
Chiba, K.
1965a. Freshwater fish culture from the viewpoint of stocking density.
Aquiculture (Sendai) 4:43-47 (in Jpn.). See Suisan Zoshoku (Fish. CUlL).
1965b. Studies on the carp culture in running water pond - I. Fish production
and its environmental condition in a certain fish farm in Gumma Prefecture.
Bull. Freshwater Fish. Res. Lab. (Tokyo) 15: 13-33.
1965c. A study on the influence of oxygen concentration on the growth ofjuvenile
common carp. Bull. Freshwater Fish. Res. Lab. (Tokyo) 15:35-47.
1980. Water quality as an environmental factor and growth of fi;h - V. Water
quality and eel production in the heated culture pond in greenhouse. Aquiculture(Sendai) 28:39-45 (in Jpn.). See Suisan Zoshoku (Fish. Cult.).
1983. Cycle of nitrogen, carbon and phosphorus in stagnant water eel pond.
In Proceedings, 12th annual meeting of eel culture research conference, p.
141-148 (in Jpn.).
EIFAC (Eur. Inland Fish. Advis. Comna.)
1973. Water quality criteria for EurJpean freshwater fish. Report on ammonia
and inland fisheries. Water Res. 7:1011-1022.
Herrmann, R.B., C.E. Warren, and P. DoudorotT.
1962. Influence of oxygen conc~nlration on the growth of coho salmon. Trans.
Am. Fish. Soc. 91: 155-167.
Hirano, R.
1967. Environmental condition in freshwater fish culture pond - I. DohyakuKenkyu 4, p. 12-16 (in Jpn.).
lIazawa, Y.
1971. An estimation of the minimum level of dissolved oxygen in the water required for normal life of fish. Bull. Jpn. Soc. Sci. Fish. 37:237-276.
Kawai, A., Y. Yoshida, and M. Kimata.
1964. Biochemical studies on the bacteria in aquarium with circulating system- I. Changes of the qualities of breeding water and baeterial population of theaquarium during fish cultivation. Bull. Jpn. Soc. Sci. Fish. 30:55-62.
Kawamoto, N.
1957. On the productivity of intensive carp culture pond. Suisangakushusei:
717-720. Tokyo Daigaku Shuppankai, Tokyo (in Jpn.).
Knepp, G.L., and G.F. Arkin.
1973. Ammonia toxicity levels and nitrate tolerance of channel catfish. Prog.
Fish. Cull. 35:221-224.
Mie Prefectural Inland Fisheries Experiment Slation.
1978. Survey of present eel culture situation. Report of effective water utilization for aquaculture, p. 1-26 (in Jpn.).
Nakamura, N.
1963. General problem of carp. Proceedings, Zenkoku kosho kasen yoshoku
kenkyu kai, No. 36, p. 25-41 (in Jpn.).
Shirabala, S.
1964. Problems of water quality in food trout production. Bull. Fac. Fish.
Nagasaki Vniv. 17:68-82.
Shizuoka Prefectural Fisheries Experiment Station, Hamanako Branch.
1978. Diurnal changes of water quality in "ayu-fish" culture pond. Proceedings, Ayu yogyo yosui kodo riyo kenkuykai, No.2, p. 23-27 (in Jpn.).
Smith, C.G., and W.G. Williams.
1974. Experimental nitrate toxicity in rainbow trout and chinook salmon. Trans.
Am. Fish. Soc. 103:389-390.
Siewart, N.E., D.L. Shumway, and P. Doudoroff.
1967. Influence of oxygen concentration on the growth of juvenile largemouthbass. 1. Fish. Res. Board Can. 24:475-495.
Tanaka, S.
1976. Studies on the recirculation system for fish culture - VI. Culture experiment with European eel. Saitamaken Suisan Shikenjo Kenkyu Hokoku, no. 35,
p. 62-64 (in Jpn.).
Tokushima Prefectural Fisheries Experiment Station, Naruto Branch.
1977. Effect of ammonium-nitrogen on the growth of ayu-fish. Proceedings,
Ayu yogyo yousui kodoriyo kenkyukai, no. I, p. 26-28 (in Jpn.).
1978. Present situation of "ayu-fish" culture. Proceedings, Ayu yogyo yousui
kodoriyo kenkyukai, no. 3, p. 32-35 (in Jpn.).

7

The technology for mass larval rearing of marine fishes has developed remarkably over the last 15 years. For example, 6.3 x 106
juvenile red sea bream, Pagrus major, and porgy, Acanthopagrus
schlegeli, 12.1-16.0 mm TL, were produced in a hatchery withina three-month period (Fushimi 1984). There have been several
reasons for the rapid and successful development of these techniques.
One of the most important is the introduction of the rotifer
Brachionus plicatilis as a food organism, and the development of
its culture (Fushimi 1984). Establishment of natural spawning intanks is another important factor. A female red sea bream of 1-1.5
kg spawns 2-3.5 X 106 eggs during a period of 1.5 months (Kitajima 1978, 1983). Furthermore, special attention to improving
environmental management for larval rearing and mass culture of
the rotifer promoted development of fry production techniques.
Thus, it has become possible to rear fry in large-scale 100-ton tanks,with a harvest of 106 juveniles of 10 mm TL, and mass culture
rotifers in 40-ton tanks, with a harvest of 152.4 x 108 rotifers, or
45 kg for 18 days (Fukusho 1979). This paper deals with the importance of environmental management in larval rearing of marine
fishes, illustrating the serious problem of lordosis in red sea bream
and the history of research aimed at its solution as an example ofsuccessful environmental management.
Lordosis, a vertebral abnormality frequently observed (30-50%)
in hatchery-reared red sea bream and other species such as the
porgy, A. schlegeli, and silver bream, Sparus sarba, is the mostserious of several kinds of deformities, i.e., scoliosis, incomplete
development of opercle bones, and pug head (Sumita 1977, Kitajima 1978, Takashima 1978, Fujita 1979, Fujita and Kitajima 1978).
Lordosis, causing a V-shaped vertebral column, is known to be induced in fish and uninflated swim bladders (Kitajima et al. 1977,
Papema 1978, Takashima et al. 1980, Iseda 1982). External
characteristics of lordosis will gradually appear in adults during
growth, although it is actually induced in the early larval stages.
Subsequently, the abnormal features of lordosis reduce the commercial value of red sea bream, despite the long-term farming effortsof the aquaculturists.
In a search for the cause of lordosis, three fields of study were
explored: I) genetics, 2) nutrition, and 3) environmental improvement.

Environmental managementof larval rearing of marine
fishes-A short historyof research to prevent
lordosis in red sea bream,
Pagrus major
KUNIHIKO FUKUSHONational Research Institute of Aquaculture
Fisheries Agency
Nansei, Mie, 516-01 Japan

CIDKARA KITAJIMA 1
Laboratory of Aquaculture
Nagasaki Prefectural Institute of Fisheries
Nomozaki, Nagasaki, 851-05 Japan

Genetic problems_

For the investigation of genetic factors, eggs were sent from one
hatchery to a second hatchery where lordosis had rarely been observed, and newly-hatched larvae from the same spawning werereared at the two hatcheries (Fujita and Kitajima 1978, Kitajima1978). Deformed individuals never appeared at the second hatchery, while lordosis was found at the first hatchery at a rate of
14.1-35.4% (Fujita and Kitajima 1978). The percentage oflordosis
varied among experimental tanks with eggs from the same parent
fish. Lordosis has occurred in almost all hatcheries in Japan, witha few exceptions. Thus, a genetic cause of lordosis might be ruled
out, although there are data to suggest that the deformity may becaused by prehatching factors, such as physiological condition of
the eggs and brood stock (Taniguchi et al. 1984).

'Current address: Fisheries Research Laboratory, Kyushu University, Tsuyazaki,
Munakata-gun, Fukuoka, 811-33 Japan.

9Figure 1
Deformed backbone (lordosis) of cultured red
sea bream, Pagrus major.

Figure 2
Lordosis in hatchery-reared red sea breamwell correlated with development of a swim
bladder. (Top) A deformed backbone with
undeveloped swim bladder. (Bottom) A normal backbone with a well inflated swim
bladder.

10Figure 3
Cross section of trunk in red sea bream. (Left) A nonnal fISh with a weU inflated swim bladder; (Right) An abnonnal
fish with undeveloped swim bladder.

Nutritional value of
initial larval feeds

investigation of their influence has not been conducted. The content of phosphorus in seawater was pointed out as an important factor
in bone formation. Larvae have been reared in various concentrations of phosphorus, but consistent results were not obtained.

_

Omega-3 highly unsaturated fatty acids (III3HUFA) such as 20:5 111 3
are important for survival and growth of marine fish larvae(Watanabe et al. 1983). Some rearing experiments suggest thatdevelopment of the swim bladder is affected by the quality of initialfeeds (Fujita and Kitajima 1978, Watanabe 1978). Rearing groups
fed on rotifers cultured with baker's yeast (III3HUFA deficient)
have a tendency to exhibit a higher ratio of juveniles with uninflated swim bladders. On the contrary, groups fed on rotifers
cultured with Chlorella, or special yeast with assimilated
1113HUFA, have lower ratios on abnormal swim bladders. Thus
nutritional improvement may reduce the deformations (Fujita andKitajima 1978, Watanabe 1978). However, the percentage oflordosis varies among fish groups given the same feeds.

Agricultural chemicals
and phosphorus

Handling of larvae and depthof rearing water_

Seed production of finfish can be divided into two phases: I) larval
or primary rearing (3-10 mrn TL fed mainly live food organisms
and held in concrete tanks), and 2) juvenile or secondary rearing(10-30 mrn TL fed mainly minced fish and held in fine-mesh net
cages hanging from rafts). Transfer of larvae into net cages fromconcrete tanks is hard and troublesome work sometimes involving
a siphoning method. Shocks to larvae during the siphoning process have been considered a cause of deformations; however, nodifference in occurrence of deformity was found among fish subjected to siphoning, provided there was careful handling with buckets
and continuous rearing in concrete tanks up to the juvenile stage
without transfer. Thus, shock through handling was ruled out asa cause of lordosis (Fujita and Kitajima 1978). The influence of
depth of the rearing tank was also examined, and a lower incidence
oflordosis was obtained in shallow water (18 cm) compared withdeeper water (87 cm) (Kitajima and Tsukashima 1982).

___

The influence of agricultural chemicals and other poisonous
substances in the rearing water (Seikai 1982) and in food organisms
such as Anemia salina (Bookhout and Costlow 1970, Fujita andKitajima 1978) were suspected of inducing lordosis, but precise11Relationship between aerationand deformation

Acknowledgments

We wish to express our sincere thanks to Warren D. Nagata and
Ryo Suzuki for their critical reading of this manuscript.

Optimal amounts of aeration for larval rearing were examined in
I-ton circular tanks. Lordosis was rarely found in fish groups rearedat an aeration rate of 50-100 mLlminute, while a high percentage
of deformity appeared in non-aerated tanks and with aeration greaterthan 500 mL/minute (lseda et al. 1982). Moderate and uniform water
currents led to lower percentages of lordosis and higher survival
rates, even without aeration; while survival rates and perc(:ntagesof fishes with inflated swim bladders were low in tanks without
aeration and current. Thus, it was found that moderate current,
suitable aeration, and weak sprinkling of water on the surface ofrearing water during the stage of mouth opening (4-6 days after
hatching) were effective methods of reducing the incidence oflordosis (lseda 1982).

Demonstration of
air gulping theory

Citations_

Bookhout, C.G., and J.D. Costlow, Jr.
1970. Nutritional effect of Artemia salina from different locations on larval
development of crabs. Helgol. Wiss. Meeresunters 20:435-442.
Doroshev, S.I., and J.W. Cornaccbia.
1979. Initial swimbladder inflation in the larvae of Tilapia mossambica andMorone saxalilis. Aquaculture 16:57-66.
Dorosbev, S.I., J.W. Cornacchia, and K. Hogan.
1982. Initial swim bladder inflation in the larvae of physoclistous fishes and its
importance for larval culture. Rapp. P.-V. Reun. Cons. Int. Explor. Mer
178:495-500.
Fujita, S.
1979. Culture of red sea bream, Pagrus major, and its food. In StyczynskaJurewict, E., T. Backiel, E. Jaspers, and G. Persoone. (eds.), Cultivation ofFish and Its Live Food. Spec. pub\. 4, p. 183-197. Eur. Maricult. Soc., Belgium.
Fujita, S., and C. Kitajima.
1978. Occurrence of the lordotic deformity in larvae and juveniles of red sea
bream. Kaiyou-Kagaku (Mar. Sci. Monthly) 107:721-727 (in Jpn.).
Fukusbo, K.
1979. Studies on fry production of Japanese striped knifejaw Oplegnalhus
fascialus, with special reference to feeding ecology and mass culture of foodorganisms. Spec. rep. 6, Nagasaki Prefect. Inst. Fish., 173 p. (in Jpn., Engl.
summ.).
Fusbimi, T.
1984. The present status of seedlings technology for red sea bream and black
sea bream, and mechanization for their mass production. In Inoue, H., (ed.),The Present Status of Development and Researches in Technology of Fisheries,
p. 68-79. Guzyutu Joho-Center, Osaka, Japan (in Jpn.).
Iseda, A.
1982. Prevention of lordosis in the juvenile of red sea bream, Pagrus majorreared in ponds - III. Relationship between the initial conditions of rearing environment and gas content. Bull. Kumamoto Prefect. Inst. Fish. 2:25-45 (inJpn.).
Iseda, H., M. Ishihara, S. Sumita, M. Owaki, and S. Tabata.
1982. Prevention of lordosis in the juvenile of red sea bream, Pagrus majorreared in ponds - 11. Relationship between the initial rearing-conditions andthe lordotic deformity. Bull. Kumamoto Prefect. Inst. Fish. 1:9-17 (in Jpn.).
Kitajima, C.
1978. Aquisition of fertilized eggs and mass-culture of juveniles of red sea bream,
Pagrus major. Spec. rep. 5. Nagasaki Prefect. Inst. Fish., 92 p. (in Jpn., Eng\.
summ.).
1983. The present status of marine fish seed producing technique in Japan. In
Fuentes, H.R., J.G. GastilIoa, and L.H. Disalbo (eds.), International Symposium on Advanccs and Perspectives of Aquaculture in Chile, p. 375-390.
Universidad del Norte, Coquimbo, Chile.
Kitajima, C., H. Iwamoto, and S. Fujita.
1977. Relationship between curvature of vertebral column and hatchery-reared
undeveloped swimbladder in red sea bream, Pagrus major. Bull. Nagasaki
Prefect. Inst. Fish. 8: 137-140 (in Jpn.).
Kitajima, C., Y. Tsukashima, S. Fujita, T. Watanabe, and Y. Yone.
1981. Relationship between uninflated swim bladders and lordosis deformity
in hatchery-reared red sea bream Pagrus major. Bull. Jpn. Soc. Sci. Fish.
47:1289-1294 (in Jpn., Engl. summ.).
Kitajima, C., and Y. Tsukashima.
1982. Effects of depth of the rearing tank on the incidence of swim bladder inflation of larval red sea bream, Pagrus major. Bull. Nagasaki Prefect. Inst.
Fish. 8:137-140 (in Jpn.).
Nagaike, N., and Y. Sasaki.
1981. The mass production and breeding in hatchery reared red sea bream,
Pagrus major (Temminck and Schlegel) - I. Mass selection of fish with abnormal airbladder. Aquiculture (Sendai) 28: 196-201 (in Jpn.). See Suisan Zoshoku(Fish. Cult.).
Paperna, I.
1978. Swimbladder and skeletal deformation in hatchery bred Sparus surata.
J. Fish. BioI. 12: 109-114.

_

Rhythmical movements toward the surface by larvae at the mouthopening stage were observed by Yamashita (1963, 1982) and thesignificance of this behavior was evaluated in view of r.ormalorganogenesis. Also, the swim bladder was found to be inflated
for short periods at the size of 3.5 rum TL, 5-6 days after hatchingat a temperature of 18-22°C (Kitajima et al. 1981). According tothese facts, it was considered that the abnormally developed swim
bladder of larvae was due to a failure to gulp air at the surface during this early stage.
Rearing experiments were conducted to examine this hypothesis(Kitajima et al. 1981). One tank was sealed with a layer of liquidparaffin and the other left open as a control. Over 90% of the larvae had normal swim bladders at about 7 days after initial feeding(4.2 rum TL) in the control tank, whereas none were inflated in
the sealed tank. Thus, it has been shown that gulping air at the surface is essential for initial swim bladder inflation (Kitajima et al.
1981). This hypothesis was proved by histological observations during the development of the swim bladder (physostomous to physoclistous stages) (Takashima et al. 1980). The importance of air
gulping during the physostomous stage was also demonstrated inother species (Doroshev and Cornacchia 1979, Doroshev et al.
1981).

Larval rearing procedures forprevention of lordosis

_

_

_

Lordosis is rarely found in hatchery-reared red sea bream at present,
since environmental conditions in larval rearing tanks have been
well managed, with the application of information and techniques
obtained through previous research, i.e., to (I) supply a moderatecurrent and aeration (50-100 mLlrnin' ton), (2) clean the surface
so that air will penetrate into the rearing water, (3) supply waterwith a sprinkler on the surface of rearing water, (4) introduce newly
hatched larvae at fairly low stocking densities (1-2 x 104 individuals/m3), (5) select individuals with well developed swim bladders by the method of specific gravity (Nagaike and Sasaki 1981)
or phototaxis (Iseda 1982), and (6) feed the larvae with rotifers ofgood nutritional value.

12

Seikai, T.
1982. Acute toxicity of organophosphorous insecticides on the developmental
stage of eggs, larvae and juveniles of Japanese striped knifejaw, Oplegnathus
fascia/us. Bull. lpn. Soc. Sci. Fish. 48:599-603 (in lpn., Eng!. summ.).
Sumita, S.
1977. Deformations found in hatchery-reared red sea bream. Spec. rep. 46, Fish.
Exp. Stn., Kumamoto Prefect., p. 33-42 (in lpn., Eng!. summ.).
Takashima, F.
1978. Vertebral malformation in hatchery-reared red sea bream, Chrysophrys
major. Bul!. lpn. Soc. Sci. Fish. 44:435-443 (in lpn., Eng!. summ.).
Takashima, F., Y. Arai, and M. Nomura.
1980. Abnormal development of the swimbladder in hatchery-reared red seabream, Chrysophrys major. l. Tokyo Univ. Fish. 67:67-73 (in lpn., Eng!.
summ.).
Taniguchi, N., K. Azuma, and S. Umeda.
1984. Difference due to parents in incidence of vertebral malformation in artificially bred red sea bream. Bull. lpn. Soc. Sci. Fish. 50:787-792.
Yamashita, K.
1963. Fundamental studies on the culture of red sea bream, Pagrus major - 1.
Ethological observation of larvae in tanks. Aquiculture (Sendai) 11: 189-209(in lpn.). See Suisan Zoshoku (Fish. Cult.).
1982. Differentiation of the swimbladder structure in larvae of the red seabream
Pagrus major. lpn. l. lchthyo!. 29: 193-202 (in lpn., Eng!. summ.).
Watanabe, T.
1978. Nutritional value of food organisms in view of lipids. In Aquaculture andLipid in Feeds, p. 93-111. lpn. Soc. Sci. Fish., Koseisha-Koseikaku, Tokyo(in lpn.).
Watanabe, T., C. Kitajima, and S. Fujita.
1983. Nutritional value of live organisms used in Japan for mass propagationsof fish: A review. Aquaculture 34: 115-143.

13

In Japan, many kinds of bivalves have been used in a variety ofrecipes. These bivalves are supplied from fishing and aquaculture.
The latter is divided into two methods: hanging and sowing. In the
hanging method, bivalves are hung from a raft or line, and put into
an environment which is different from that of their natural habitat.
Thus, the species suitable for the hanging culture method must havean ability to tolerate the change of environment. In the sowing
method, the environmental conditions of the culture grounds arealso very important for the growth and survival of the planted
bivalves. Accordingly, knowledge of the physiological and ecological characteristics of bivalves, and their limits of tolerance forenvironmental conditions, must be accumulated in more detail forfurther development of management techniques and culture methods.
Previously, the relationship between habitat and osmoregulatory
ability of bivalves, with special reference to free amino acids foundin body fluids, was reported at the UJNR meeting in 1981 (Wada
1984). The present paper deals with shell-closing behavior of several
species of bivalves and their ability to tolerate salinity changes.

Salinity tolerances ofmarine bivalves
SHOJI FUNAKOSHITOHRU SUZUKI
KOJI WADA
National Research Institute of Aquaculture
Fisheries Agency
Nansei, Mie, 516-01 Japan

Materials and methods_

Experiments were carried out with II species of bivalves (commercial size) shown in Table I. After collection, the bivalves were
kept in basket nets at Ago bay, Mie Prefecture, for at least I week
before use. The samples of each species were divided into twogroups. One group was used for examining the behavioral responseof closing the shell valves tightly after salinity changes. In the second group, a plug was inserted between shell valves to allow theexternal medium to enter the mantle cavity freely; this group wasused for determination of salinity tolerance limits. The bivalves ofeach group were transferred into five containers filled with 25,50,
100 (full-strength), 150, and 200% seawater, and maintained for
2 days. All the media were changed every day. Lower salinity media
were prepared by diluting seawater with wellwater, and high salinity
media by adding instant ocean salts to seawater. The experiments
were conducted at water temperatures of 22-24 °C with the exception of 14°C for Patinopecten yessoensis, which lives in cold seas.

Determination of osmotic pressure
Mantle cavity fluid, hemolymph, and the seawater medium were
sampled at 2-4,24, and 48 hrs of exposure to each medium. Theirosmotic pressures were measured with a freezing-point depression
osmometer (Advanced Instruments, Inc., Model 3CII).

Determination of survival
Three to five individuals of the plugged group in each medium were
removed from the container to the basket net, and suspended froma raft at 2-4, 24, and 48 hrs of exposure. After one week, theirsurvival was determined.

15

Table 1
Survival (%) and osmotic pressure (mOsM/kg) of hemolymph at the lowest (min.) and highest (max.) concentrations without mortality
observed in the plugged bivalves aftel: 48 hrs of exposure to various concentrations of seawater.
Survival
Concentration of seawater(osmotic pressure)

Osmotic pressureof hemolymph

Species

25%
(240)

50%
(480)

75%
(730)

100%
1960)

150%
(1500)

200%(2000)

Crassostrea gigas
Mytilus edulis
Meretrix petechialis
Mytilus coruscus
Scapha rca broughtonii
Pinctada fucata
Mactra (M) chinensis
Chlamys (M) nobilis
Fulvia mutica
Patinopecten (M) yessoensis
Pecten (N) albicans

100
100
100
0
0
0
0
0
0
0
0

100
100
100
100
100
0
0
0
0
0
0

100
100
100
100
100
100
100
100
100
66
0

100
100
100
100
100
100
100
100
100
100
100

100
100
66
33
0
0
0
0
0
0
0

100
0
33
0
0
0
0
0
0
0
0

Results

_

Min.

Max.

300
310
420
470
510
710
720
720

2000
1460
960
960
960
960
960
960
960
960
960

no
960
960

of salinity tolerance could isolate themselves from the external
medium by tightly closing their valves for a longer time than thosewith a narrow range of salinity tolerance. Figure 1 indicates theresults of tests with bivalves with wide (Meretrix petechialis),
moderate (Mactra chinensis), and narrow (Pecten albicans) rangeof salinity tolerance.

Salinity tolerance
Table I shows the survival at 48 hrs of exposure to the experimental media, and the osmotic pressures of hemolymph at the lowest
and highest seawater concentrations which were tolerated. Species
in Table I are listed in order based on the range of salinity tolerance.
When the plugged bivalves were put in the experimental media,
their hemolymph and mantle cavity fluid soon reached osmotic
equilibrium with the external medium, but the mantle cavity fluidof the oyster, Crassostrea gigas, the edible mussel, Mytilus edulis,
and the clam, Meretrix petechialis, in the 25 and 50% seawaterremained hyperosmotic to the media to some extent, because theanimals prevented the medium from entering the mantle cavity byloosely closing the edges of the mantle palps.
Crassostrea gigas withstood the full range of the 25,50,75, 150,
and 200% seawater for 48 hrs. Mytilus edulis survived 48 hrs of
exposure to the 25,50,75, and 150% seawater, but all individuals
had died at 24 hrs in the 200% seawater. Meretrix petechialis survived for 48 hrs in the 25, 50, and 75 % seawater. The pearl oyster,
Pinctada fucata, the surf clam, Mactra chinensis, the scallop.
Chlamys nobilis, and the cockle, Fulvia mutica, withstood only 75%
seawater for 48 hrs, and all of them had died at 48 hrs in the 25,
50, 150, and 200% seawater. But the occurrence of mortality withtime in the 50% seawater was different interspecifically. At 24 hrs
exposure to 50% seawater, P. fucata showed 33% mortality, andC. nobilis, M. chinensis, and F. mutica showed 100 % mortality.
The scallop, Pecten albicans, could not withstand either diluted orconcentrated seawater even for 24 hrs.

Meretrix petechialis-At 2-4 hrs of exposure to the 25, 50, 75,
150, and 200% seawater, the clams isolated themselves from themedium by closing their valves tightly, and the osmotic pressuresof mantle cavity fluids were maintained at 940-960 mOsM/kg,
similar to that of 100% seawater (950 mOsM/kg), regardless ofthe osmotic pressure of the external medium. At 48 hrs, the mantle cavity fluids became almost isotonic to the external medium inthe 50 and 75% seawater; however, both in the 25 and 200%
seawater, the mantle cavity fluids were still kept hyperosmotic andhyposmotic to each external medium by closing the valves tightly.
Mac/rOo chinensis-In the 150 and 200% seawater, the mantle cavity
fluids became isosmotic to each external medium at 2-4 hrs. The
animals did not isolate themselves from these high-salinity media
even for 2-4 hrs by closing their valves. After 2-4 hrs of exposure
to the 75 % seawater, in which the clams could survive for at least48 hrs, the mantle cavity fluids became also isosmotic to the 75%
seawater. However, in the 25 and 50% seawater, the mantle cavity
fluids were hyperosmotic to the media at that time. The mantle cavity
fluids at 24 hrs of exposure to the experimental media were isosmotic
to each medium, with the exception of a slightly hyperosmotic state
observed in 25 % seawater.
Pecten albicans-In the 25, 50, 75, 150, and 200% seawater, themantle cavity fluids were isosmotic to the external media at 2-4
hrs of exposure, with one exception out of three scallops which
maintained a hyperosmotic state in the 50% seawater. Most scallops
could not close their valves tightly even for 2-4 hrs with the sudden salinity changes.

Shell-closing
Some bivalves can isolate themselves from unfavorable conditionsof the environmental medium by closing their valves. This behavior
was examined by measuring the osmotic pressures of the hemolymph, mantle cavity fluid, and external medium. Hemolymph wasusually at osmoequilibrium with mantle cavity fluid, with exceptions observed in some species at 2-4 hrs in the 25 or 200% seawater.
The results clearly indicated that the bivalves with a wide range
16

24 hrs

2-4 hrs

48 hrsM. petechialis
2000

MedY

7"
.
.
.
1000

C)

~

"oE
o

.§.

M. (MJ chinensis
2000

/

!

~

/

en
en

!Q.

~

/

..
CJ
.-

o

E
en

P. (N.) albicans

o

2000

1000
/

/

../

<illl$

~/

/
100

200

100

200

100

200

Concentration of sea water (0/0)
Figure 1
Changes in the osmotic pressure of the hemolymph (0) and the mantle cavity (+) of Meretrix petechialis, Mactra (M.) chinensis, and Pecten (N.)
albicans at 2-4, 24, and 48 hrs of exposure to 25, 50, 75, 100, ISO, and 200% seawater.

17

Discussion_

Citations

Marine bivalves are osmoconfonners. Their hemolymph is in osmoequilibrium with the external medium. They can adapt to environmental salinity changes by regulating the concentrations of ions andintracellular free amino acids (Robertson 1964, Somero and Bowlus
1983). The range of salinity tolerance, however, is different among
species and affected mainly by the size of the free amino-acid poolavailable for intracellular volume regulation (Gainey and Greenberg
1977).
When salinity changes occur in the environmental medium,besides the adjustment by metabolic regulation mentioned above,
bivalves can also close their valves tightly, retreat into burrows,
or escape from unfavorable salinity by swimming, depending on
their capabilities for movement.
The habitats of the bivalves used in this experiment are as follows.
Crassostrea gigas is common in the intertidal zone and attaches
to rocks. Mytilus edulis and Meretrix petechialis live from theintertidal zone to the upper part of the infralittoral zone where thesalinity is changeable. The former is an attached surface-dweller
and the latter a sandybottom burrower. Mytilus coruscus and Pinctada fucata live in the upper part of the infralittoral zone and are
surface dwellers. Chlamys nobilis is found in the upper part of theinfralittoral zone and lives freely or attaches only weakly to thebottom surface by byssus threads. Mactra chinensis, Scapharcabroughtonii, and Fulvia mutica are bottom burrowers in the upper
to middle part of the infralittoral zone. Patinopecten yessoensis andPecten albicans live freely on the bottom surface in the middle tolower part of the infralittoral zone.
Crassostrea gigas, M. petechialis, and M. edulis live in the intertidal zone or shallow water with changeable salinity. They can withstand a wide range of salinity, and were found to be able to close
the shell valves tightly for a long time. On the contrary, P. yessoensis and P. albicans were found to withstand diluted or concentrated seawater media poorly, due to lack of ability to close theirvalves tightly and continuously for a long time. Consequently, thefollowing conclusions were reached. Bivalves living in the intertidal zone and shallow water with changeable salinity can wait forrecovery of salinity by closing their valves tightly after sudden salinity change of ambient water, and can also adapt themselves to awide range of salinity by metabolic regulation. The bivalves, whichlive in the lower part of the infralittoral zone and can also swim
with well developed adductor muscle and mantle palps, have poor
metabolic abilities for osmoregulation, but they can escape from
unfavorable salinity conditions by swimming.
In a long evolutionary history, in which bivalves have dispersed
into various habitats, they have adaptively acquired the metabolic
function and behavior suitable for these habitats. The knowledgeof physiological and ecological characteristics will provide valuable
information for the development of culture techniques. For example, the abovementioned knowledge of behavior in the presence ofsalinity changes could be useful in the search for suitable culture
grounds and in the management of culture by the hanging method.
The knowledge about shell-closing ability has been used in brine
treatment (Waki and Yamaguchi 1964) to extenninate the mudworm, Polydora, which penetrates the shells of pearl oysters. An
outline of the treatment is as follows: The pearl oyster is first dipped
into freshwater for 15 minutes to make shell valves close tightly,
and then in 22 % brine for 20 minutes. By this treatment Pol)dora
is killed without any mortality of the pearl oyster.

_Gainey, J.F., Jr., and M.J. Greenberg.
1977. Physiological basis of the species abundance-salinity relationship in
molluscs: A speculation. Mar. BioI. 40:41-49.
Robertson, J.D.
1964. Osmotic and ionic regulation. In Physiology of Mollusca, Vol. I, p.
283-308. Acad. Press, NY.
Somero, G.N., and R.D. Bowlus.
1983. Osmolytes and metabolic end products of molluscs: The design of compatible solute system. In The Mollusca, Vol. 2, p. 77-100. Acad. Press, NY.
Wada, K.
1984. Osmoregulation in marine bivalves. In Sindermann, C. J. (ed.), Proc.
9th/10th U.S.-Japan Meetings on Aquaculture, p. 89-92. NOAA Tech. Rep.
NMFS 16 (Nat!. Oceanic Atmos. Adm., Natl. Mar. Fish. Serv.), Seattle, WA
98115.
Waki, S., and K. Yamaguchi.
1964. Extermination of mud worm, penetrating into the shell of the pearl oyster,by brine treatment. Kaiho 64: 15-25. Natl. Fed. Pearl Cull. Co-op. Assoc. (inJpn.).

18

Temperature preference ofimmature horse mackerel,
Trachurus japonicus, ina vertical temperature
gradient

In the past, there was concern in Japan that heavy mortality of fishes
inhabiting coastal waters might occur when large-scale fossil fueland nuclear power plants were constructed in order to meet the increasing demand for electric power, and huge amounts of thermal
effluent would be released into coastal areas. However, mortalityof fish caused by the thermal effluent has been found to be negligible in recent years. Therefore, research into thermal effects on
fishes has concentrated on behavioral studies.
One of the fish behavioral programs related to thermal effluent
from power plants is a study of the temperatures preferred andavoided by various fish species. The Marine Ecology ResearchInstitute is presently conducting studies of this kind using commercially important fishes which inhabit the coastal waters of Japan.
The research is conducted under laboratory conditions, with thefinancial support of the Japanese Government.
In the study reported here, behavior of horse mackerel, Trachurusjaponicus, an important coastal fish, was examined in a verticaltemperature-gradient aquarium.

ASTUSHI FURUKAWA 1
HIROSHI FUKATAKISHUJI TSUCHIDA
Marine Ecology Research InstituteCentral Laboratory
Iwawada, Onjuku Isumigun,
Chiba, 299-51 Japan

Materials and methods_

Immature horse mackerel, Trachurus japonicus (Temminck et
Schlegel), used in this study were of culture origin. Fish cultured
in fish farms in Shizuoka Prefecture were brought to the laboratory in October 1983. Fish were kept in 0.5 m3 indoor stock tankswith a continuous flow of sand-filtered seawater and fed a moist
diet prepared with commercial sea bream feed supplemented by
raw fish. Rearing temperature of the fish was not controlled. Holding mortality was negligible.
Prior to the experiment, the fish were randomly divided into threegroups. Each group was transferred from indoor stock tanks toacclimation tanks (3 m3) located in a rearing room and acclimatedto one of three temperatures (20, 25, and 28°C). Fish were acclimated to these temperature levels at a rate of 1°C per day andheld at the final temperature level for at least one week. During
this period, the fish were fed twice a day.
The vertical ternp~rature gradient device used in this study has
al ready been reported at the annual meeting of the Japanese Societyof Scientific Fisheries by Fukataki and Tsuchida (1986). This device
can be divided into three parts: experimental aquarium, temperature
control system, and monitoring and recording system. The experimental aquarium (Fig. I) (183 cm deep, 172 cm long, and 74
cm wide) was situated in a lightproof room. A plexiglass panel wasplaced in front of it through which the fish were observed by amonitoring video camera. Horizontal lines were drawn on the backpanel to delineate observational zones of equal width (15 cm). These
were numbered from I to II in order of decreasing depth. Total
seawater volume in the aquarium was approximately 1,485 liters.
Light was supplied by three pairs of 40-watt fluorescent lamps
suspended over the center of the aquarium.
The temperature-controlled water entered the experimental aquarium through eleven water inflow pipes arranged at intervals of IS
cm vertically on the left side of the aquarium, and flowed out througheleven water outflow pipes on the right side of the aquarium.
The desired thermal gradient in the aquarium was determinedby the temperature-control computer system (Fig. 2). Vertical watertemperature profiles were measured with a series of eleven platinumlPresent address: Yokohama-shi, Isogo-ku, Mori, 1-5-21-1036 Japan.

191---------- 1720 - - - - - - - - - - l..,...
a-".!..

H},.-t-_ ......... ""................ - ""'-_/}

Figure 1
Schematic diagram of vertical temperature-gradient tank.

Procedure_

Thermometer (11 units)
for temperature control

At the beginning of each experiment, the initial water temperaturein the experimental aquarium was adjusted to correspond with theacclimation temperatures (20, 25, and 28°C) of the particular test
group. Five fish were chosen at random from one of the acclimation tanks, transferred to the experimental aquarium of the sameacclimation temperature, and held there for about 24 hours. Thisacclimating period was necessary for fish to adjust to the newcondition.
Control observations were made to evaluate fish response toabsence of a temperature gradient. The vertical position of eachfish was recorded and put in the computer at 3-minute intervals
for I hour (designated a "unit"). Then a desired temperature
gradient was established by circulating seawater supplied througheleven water inflow pipes of the temperature-control system following the orders of the computer. Two sets of temperature differences(20 and lO°C) between surface and bottom of the aquarium wereapplied in this study. The temperature gradients set in the experimental aquarium were shown as 20°C1150 cm and WOC/150 cm,
respectively, because the water depth in the aquarium was 150 cm.
A practical process of changing water temperature in the aquarium was shown in Figure 3. This process was repeated in six setsof experiments and was usually divided into eight periods as follows.

Heat exchanger\(11 urnts),.---------::::--l

Pump (11 units)
Vertical gradient tank=---------------=::JThermometer(11 unitsl
for recording

Figure 2
Schematic diagram of temperature~ontrolsystem and the circulation of seawater.

resistance thermometers set in the eleven water outflow pipes. The
temperature data obtained were entered in the computer.
The positions of fish in the aquarium were monitored by video
camera set up in front of the aquarium, and data were entered in
the computer by means of a digitizer. The thermal gradient in theaquarium could be shifted up or down by adjustment of the ':emperature-control system.

Isothermal period (IP)
1st temperature shifting period (TSP)-desired temperature
gradient and range were formed.
1st stable temperature gradient period (STGP)-"20°C gradient" and the desired temperature range continued for I hour.

20

....... .................................................
.
.
:..::..:.>..........................................::.::'::-..-.- - - - - - - - - - - - - - - - - - - i.............................................................
.'. '. .
..................................

E--------""...........................................................................::::::::::::::::::::::::::::::::::::::::::::::::::------t................
1s t

T. S . P.... ,'········f~·~···········fi~~·:·~·~·~··f 2 nd ~~~ . G . P 3 r J ~.~~...~.:~.: G . P

E-------------S . T . G. P

2

T.S.P

4

5

Time

( hours

3

T.S.P

6

7

8

9

Figure 3
Process of temperature change in each zone. IP = isothermal period; TSP = temperature shifting period; STCP = stable temperature gradient period. Arrows
indicate period boundaries.

Results and discussion

2nd stable temperature gradient period-same conditions as thatof 1st STGP continued for about I hour.

_

Sizes of fish used in this study are shown in Table I. During theisothermal period, fish distributions were not consistently symmetrical (Fig. 1). This suggests that the conditions in the aquarium
were not homogeneous for all fish groups. As mentioned earlier,
three pairs of 40-watt fluorescent lamps were suspended over thecenter of the aquarium and the light intensity at the water surface
was 60-80 lux. It has been reported that rainbow trout, Salmo
gairdneri, at 220 and 2200 lux displayed a definite affinity for theupper part of the tank during the first 4 months of life (K wain and
McCauley 1978). Although experiments on the effect of illumination on the distribution of horse mackerel in isothermal conditions
were not carried out in the present study, no remarkable change
in distribution of fish was observed. Based on these results, theoverhead illumination was used throughout the experiment without
special consideration.
A summary of observations on preferred temperature of horsemackerel at three acclimation temperatures (20, 25. and 28°C) isshown in Table I. The maximum range of water temperature
occupied by fish acclimated to 20°C at the stable temperature gradient period (keeping watertemperature at 15-35°C) was 17-30°C;
in the case of the 25°C acclimation temperature, the maximum range
was 20-31 °C; and in the case of28°C, it was 18-31 °c. From theseresults, the temperature range occupied by immature horse mackerel
was thought to be fairly wide. This fact agrees well with the wide
distribution of horse mackerel in natural habitats.
Temperature appeared to be the dominant factor influencing fish
distributions in a vertical temperature gradient aquarium, since theposition of the mode of distributions moved in accord with the location of preferred temperature (Fig. 5).
Usually, preferred temperature has been defined as the temperature most frequently occupied when fish are held in temperature
gradient conditions for a long time. On the other hand, Ingersoll

2nd temperature shifting period-desired temperature gradientand range were formed.
3rd stable temperature gradient period-"lOoC gradient" andthe desired temperature range continued during this period.
3rd temperature shifting period-temperature range was shiftedto another desired range leaving" WOC gradient."
4th stable temperature gradient period-desired conditions continued during this period.
In temperature selection experiments, six sets of observations weremade to evaluate response to a thermal gradient. The position ofeach fish and water temperature in the aquarium were recorded at
3-minute intervals throughout the experimental period, but only dataobtained from each stable temperature gradient period were used
to determine the thermal behavioral response of fish.
The average temperature and its standard deviation in each zone
during the stable temperature gradient periods were calculated from20 temperatures and stored in the computer.
The role of temperature as the main factor controlling the distribution of fish in an aquarium was recognized through the observation of changes of the temperature gradient and shifts in fish
distribution. Fish distributions in the aquarium were shown aspercentage frequency distribution of the observational zone occupied by fish during a unit (5 fishx20 times = 100 observations).
These frequency distributions were then compared with the temperature gradient to determine the temperature preferred by the fish.
After the experiment, body length and weight of each fish were
measured.

21

Table 1
Summary of observations on the temperature preferred by horse mackerel at three acclimation temperatures.
Experiment no.

Body length (em)
(0C)

Mean

SD

Period no.

Temp. range
in aquarium
(OC)

20

20.8

1.8

1st
2nd
3rd
4th

20

20.4

1.5

25

19.5

25

Acclimation temp.
(Group no.)

Range

Mean

SD

15.6-34.9
15.6-35.0
18.6-27.6
15.3-24.7

18.7-24.8
20.8-26.9
19.9-23.0
19.4-22.4

23.0
23.6
22.4
21.3

1.5
1.1
0.8
0.8

1st
2nd
3rd
4th

15.1-34.7
15.1-34.7
18.3-28.2
15.7-24.3

17.1-27.0
18.6-24.0
21.0-24.1
19.5-23.1

22.9
23.3
22.9
21.1

1.8
1.2
0.8
0.8

1.0

1st
2nd
3rd
4th

15.0-35.2
15.1-35.2
18.2-27.9
18.2-28.0

20.9-31.3
20.9-29.4
19.7-26.7
19.7-26.7

25.6
25.4
24.5
24.9

1.5
1.4
1.6
1.0

20.4

0.7

1st
2nd
3rd
4th

15.2-34.9
15.1-34.9
18.7-27.5
22.5-31.9

21.0-29.2
23.5-29.2
22.4-26.6
23.4-27.3

25.2
25.5
25.2
25.6

1.7
1.3
0.9
1.1

28

20.8

1.0

1st
2nd
3rd
4th

15.1-35.0
15.2-35.0
18.2-27.9
18.2-28.0

21.0-27.0
18.8-29.3
21.1-27.0
21.0-27.0

25.5
25.3
24.9
24.8

1.4
1.5
1.3
1.2

28

23.2

1.6

1st
2nd
3rd
4th

15.3-35.0
15.3-35.0
23.2-32.7
23.1-32.7

18.5-31.1
21.1-28.9
24.3-27.9
24.3-27.0

24.4
24.8
25.0
24.8

1.8
1.3
0.8
0.7

(I)

II

(2)

111
(I)

IV

(2)

V
(I)

VI

Temp. occupied by fish (0C)

(2)

Acknowledgments

and Claussen (1984) used two methods to determine preferredtemperature of laboratory animals: the acute thermal preferendum(obtained within 2 hours or less after animals have been placed ina gradient) and the final temperature preferendum (obtained after
24-96 hours in a gradient). The preferred temperature was obtained
within l hour in our study. Therefore the result is considered toshow the acute thermal preferendum rather than the final temperature preferendum.
The relationship between acclimation temperature and mean
preferred temperature (mean of occupied temperatures in Table I)
is shown in Figure 6. Immature horse mackerel acclimated to l4,
20, or 25°C preferred temperatures higher than the acclimation
temperature, while fish acclimated to 26 or 28°C selected temperatures lower than the acclimation temperature. The data were best
fitted by the equation_

We would like to express appreciation to the Ministry of International Trade and Industry for funding and use of laboratory facilities.
We also would like to thank Miss K. Matsumoto for her assistancein preparation of the manuscript.

Citations_

Fukataki, n., and S. Tsuchida.
1986. Structure and efficiency of the new vertical temperature gradient device.
Spec. rep. I, p. 47-72. Mar. Eco!. Res. Inst., Chiba, Japan.
Kwain, W., and R.W. McCauley.
1978. Effects of age and overhead illumination on temperatures preferred byunderyearling rainbow trout, Salmo gairdneri, in a vertical temperature gradient. J. Fish. Res. Board Can. 35:1430-1433.
Ingersoll, C,G., and D.L. Claussen.
1984. Temperature selection and critical thermal maxima of the fantail darter,
Etheosroma flabellare, and johnny darter, E. nigrum, related to habitat andseason. Environ. Bio!. Fish. II (2): 131-138.
Yamada, T.
1969. On the distribution and the fishing ground of horse mackerel in Japan
Sea. Bull. Fac. Fish. Nagasaki Univ. (28)111-130.

Tp = 1.33TA - 0.03TA 2 + 7.37 (R2 = 0.82),

where Tp is preferred temperature, and TA is acclimation temperature. The acute thermal preferendum, the point where Tp = TA,
was 24.9°C.
The range of all preferred values obtained from three acclimation temperatures was wide (17-31 0c) and included the range oftemperatures found in coastal area habitats (l5-26°C) and fishinggrounds for the immature fish (I6-25°C) (Yamada 1969).

22

'C
30,--------------------"

60
Acclimation level 28° C
Isothermal condition 28° C

50
40
30

25
<lJ

20

'-<

:l

.w

10

'lJ

'-<
<lJ

~

0

20

<lJ

~

50

Acclimation level 25° C
Isothermal condition 25° C

"..
>,

<lJ
U

c:

40

<lJ

0

c

Q)
~

'-<

~

30

0'

...
Q)

"-

15

<lJ

'-<

20

0..

10

10 "'---10

0
60

.l.-

--l..---l..-

15

20

25

Acclimation Temperature

--l

30'C
TA )

50

Figure 640

Relation of preference temperature to acclimation temperature in horse mackerel.

30
20
10
0

Figure 4
Percentage frequency-distribution of zone occupied by fish in the isothermal period. Unshaded bars are group I and shaded bars are group 2.

Surface

35

10

33

33

9

31

31

0
N

l

7

27

6

25

5

23

4

J

~

29

I

28

I

31

26

29

30

>

I

25

I

I

25

~23

r

22

20

2

17

17

19

1

15

15

18

20

Frequency

60

40

%

U
20

Frequency

40%

Figure 5Distribution of horse mackerel corresponding to the temperature shift in aquarium.

23

I

26

24

19

40

27

25

19

%

28

21

3

20

29

n

23

21

Frequency

I

24

21

Bottom

32

h"

27

I

'C

'C

'C

35

8
<lJ
C

'C

11

23
22

20
Frequency%

The king crab (Paralithodes camtschaticus) , Hanasaki crab (Paralithodes brevipes) , horsehair crab (Erimacrus isenbeckii), and snow
crab (Chionoecetes opilio) are the main species of coldwater crabs
for which mass-cultivation of larvae and postlarvae is being studiedin Japan. The king crab is one of the most important fisheries inJapan, and studies of techniques of cultivating larvae and propagation have been conducted since 1940 (Kaai 1940, Sato 1958, Kurata
1959, Nakanishi 1976, Omi 1980, Nakanishi and Naryu 1981). The
snow crab is also one of the most important fisheries in Japan, andthere have been several reports on the fisheries and resources (Ogata
1974, Kon 1980). However, studies on rearing of larvae and propagation of snow crab and other coldwater crabs have been conducted
mainly since 1970. Such mass-cultivation is being conducted atMarine Cultivation Centers under prefectural management and withthe cooperation of the Japan Sea Farming Association. At present,
the numbers of seedlings of king crab and Hanasaki crab exceed
200,000, and there are about 1,000 seedlings of snow crab.
When larvae and postlarvae are cultured, it is important to know
the effects of the environment. One of the most important environmental variables affecting marine organisms, especially those livingin the cold sea, is temperature. In culturing the larvae of coldwater
crabs, it is necessary to maintain the ambient seawater at a lowtemperature (8°C or lower). But in order to culture these larvae
for a rapid growth rate and at low cost, it would appear advantageous to culture them in warm water. However, there is little information about temperature effects on the success of masscultivation of crab larvae and postlarvae. Thus, this report mainly
concerns the effects of water temperature.

Effects of environment
on seedlings of the king crab,
Paralithodes camtschaticus
TAKASHI NAKANISHI
Japan Sea Regional Fisheries Research Laboratory
5939-22, 1 Suido-cho,
Niigata, 951 Japan

ABSTRACT
In order to determine optimum environmental conditions for the mass-cultivationof eggs, the effects of temperature, hypoxia, and salinity on the survival rate,
growth, and respiration of king crab larvae and postlarvae were studied. Optimum temperature from fertilization to the zoea egg stage is 3-8°C, and 3°C
from this stage to batching. The optimum temperature for mass-cultivation oflarvae and postlarvae is 8°C. The optimum condition of oxygen saturation is morethan 80%, and of salinity is 26.8-40.2.

Life history_

Eggs adhere to abdominal pleopods of king crabs where they arebrooded for about 300 days until they hatch. There are fourplanktonic zoeal stages. After approximately 30 days at 8°C, zoeae
molt to glaucothoe that are able to swim but whose morphology
is crab-like. The glaucothoe stage molts to become a young, bottomdwelling crab that cannot swim. In this discussion, the egg stage
is abbreviated as "E" (e.g., the egg stage at 100 days after spawning is shown as E-l00), the zoeal stage as "Z," the glaucothoe
stage as "G," and the young crab stage as "C."The change in size from egg stage (the embryo) to the young
crab stage is indicated by wet weight (Fig. I-A). It increased exponentially with time (days). The regression line was bent at C-3,
and the gradient of the weight declined. The king crab molts more
frequently, but the growth rate is slower than that of the snow crab.
At Z-4, G, and C-l, there were large morphological and ecologicalchanges, but the dry weight, wet weight, and carapace length at
Z-4, G, and C-I were nearly the same (Nakanishi et al. 1974); inother words, there may be no growth during these stages.
Oxygen consumption also increased exponentially with time, andthe regression line was bent at C-3 (Fig. I-B). The oxygen consumption at E-300, Z-I, Z-2, G, C-I, and C-2 was under the regression line.

25

ImgJ

O2 com.
( JlP/hr. indo )

1000

1000

100

100

10

10

'11.'11.

·C2
G.C,

"i4

·Z3
·Z2

·e~J~
0.1

0.1

·egg2
0.0 I • egg I

O.QI

A

B

0.00 I L-_..L-_..L-_...I...-_..L-_..L-_--'--_..L-_..L-_-'o 100 200 300 400 500 600 700 800 900

0.00 I ' - - _ ' - - _ ' - - _ ' - - _ ' - - _ ' - - _ - ' - - _ - ' - - _ - ' - - - - - - Jo100
200 300 400
500 600 700 800 900(days)( days)Figure 1(A) Relationship between wet weight (WW, mg) and the term (days) at 3°C at egg stage and at SoC at larval stage, and (B) relationship between
oxygen consumption {jALih per individual) and the term (days) at SoC.

Egg stage_

the survival rate at 5 weeks was 100% at -1.8,3, and 8°C, 20-70%
at 13°C, and 20-30% at 18°C. At E-I66, the survival rate at 5 weeks
was 100% at -1.8,3,8, and 13°C, and 90% at 18°C. At E-258,
the survival rate decreased with increasing water temperature. Fifty
percent of the eggs died 4 weeks later at 8°C, 3 weeks later at 13°C,
and 2 weeks later at 18°C.

The effect of water temperature on the survival and development
rate at E was studied by cultivating egg-bearing females at approximately 3°C and 8°C in fiberglass flow-through (I L/min.) tankswith a sand filter. Frozen squid, shrimp, and sardines were supplied for food. The experiment started with four crabs at 3°C andwith three crabs at 8°C.
Egg clutch volumes at 8°C decreased rapidly from E-40 and were
under 10% at E-70, while egg clutch volumes at 3°C decreased
gradually, and were 10-80% when the larvae hatched (Fig. 2-A).
The yolk volume at 8°C decreased rapidly from E-120, while thatat 3°C decreased slowly from E-150 (Fig. 2-B). The egg-bearing
females mated in the laboratory were cultured at 3°C, and the developmental stage of their eggs (Fig. 2-c-d) was regarded as a standard egg development in order to compare with the developmental
stages of the eggs between 8°C and 3°C. The developmental stagesof eggs at 3°C were the same as the standard. But those at 8°C
were faster than the standard, and there were many fluctuationsin the morphological development. The egg development of E-170
at 8°C was the same as that ofE-270, i.e., E-3oo at 3°C (Fig. 2-C).

Egg development
Comparisons of egg development between experimental and standard groups are discussed in the same way as reported previously
for long-term cultivation of egg-bearing females (Fig. 4). Growthrate increased with the increase in water temperature, but at E-23
the growth rate at 13°C was higher than that at 18°C. The sizeof embryos cultured at higher temperatures at E-23 , E-57, and E-166
was smaller than embryos cultured at 3°C. At E-258, there wasno morphological change even when the water temperature increased, and many larvae hatched out with the increase in watertemperature. However, the survival rate at the larval stage was notsatisfactory .

Hatching rate
Survival rate

The effect of water temperature on the hatching rate of eggs wasstudied. Eggs were removed from females' pleopods at 4 and 18
days before the larvae would have hatched normally at 3°C. These
eggs were cultured at -1.8, 3, 8, 13, and 18°C in bacteria-freepetri dishes with 30 mL seawater for 6 days, and the hatching rateof eggs at each water-temperature condition was observed daily.

In order to know the effects of water temperature on development
and survival rate at the egg stage, eggs removed from the females'
pleopods at E-23, E-57, E-166, and E-258 were cultured at -1.8,
3,8,13, and 18°C (Fig. 3). Culturing was done in a bacteria-freepetri dish with 30 mL seawater for 5 weeks. At E-23 and E-57.
26

W. T. 3 't

ratio
(%)

W. T. 8 t

100......... _------------' ...

d

'. b

A 50
. . . . . ------, a
a

'.. b

O~--'---'---'----'---'-----JL..J---'----L-..L----'--'-'---'

100

B 50
a

o L-.....J..-J'----'-_.1...--l.__.1.!.L.'_.1...-....1-_-'----'---'-.........

b

100

a

C 50
OL-__'__.....:L.___L___'___'__U---'-___L___'____'_.....u---'

150

300
12 I 2 318 23 2013

(days) 0

month 4 5 6 7
day

21 18 15

8

20 21

9

10 /I
25 1721

o

150

4 5

6

7

8

9

21 18 15 20 21

25

300
10 II
17 21

12 I
8 23

Figure 2(A) Egg clutch volumes (100% at the start ofexperiment), (B) ratio of volumes of yolk (byobservation of fresh samples), and (C) relationship between egg development at each experimental condition and the standard (c-d) atwater temperatures (WT) of 3° and 8°C.

W.T.

<'C)
1 8

~

13

~~

!lO
0

8

100

3
-1.8

,.
13

A

B

100

~

•
3
-1 .•

100

c
2

3

4

5

2

27

3

4

D

Figure 3

5 (weeks)

Effect of water temperature on survival rate of
eggs. Days post-spawning: (A) 23 days, (B) 57
days, (C) 166 days, and (D) 258 days.

ratio
("!oj

100

A
80

60
13(Cl
18

40

~

B

18("C)

13
8

--:-~
3
•
d;-1.820

3-1.8-----l-

100

0

C

----

80

60

18

C

181C)
13
8

.-- ------::::::;:; ~3 ("C )

!__

3

__e

-1.8

3
--1.8

40

20
L--L_-L_---L_---L_---l....2
3
4
5

2

3

4

5

Weeks later

Figure 4
Effect of water temperature on egg development compared with standard development (dotted line).
Days post-spawning: (A) 23 day" (B) 57 days, (e) 166 days, (D) 258 days.

Egg-bearing females cultured at 3-8°C

In the experiment using eggs removed 18 days before normal hatching, there was no hatch at -1.8 and 3°e for 6 days, but larvae
hatched 4-5 days later at 8°e, 3 days later at l3oe, and 2 days
later at 18°e (Fig. 5-A). In the experiment using eggs removed
4 days before normal hatching, larvae hatched 3 days later at 8°e
and 1-2 days later at 13 and 18°e (Fig. 5-b). Raising the temperature was an easy method of ensuring equal growth rate. However,the survival rate of postlarvae was low; therefore it was dangerous
for eggs to be exposed to warmer temperatures just before hatching.

These data suggest that the temperature from 3 to 8°e represents
an optimum temperature for the development to the zoea egg stage(about 200 days after spawning at 3°C), and 3°e represents an optimum temperature after the zoea egg stage. So egg-bearing females
were cultured at 8°e and at 6°e from E-120 to the zoea egg stage,
and from this stage, the rearing-water temperature was decreased
gradually to 3°e. Egg-bearing females were cultured at 3°e until
the larvae hatched (Fig. 7). The egg clutch volume was 80% when
the larvae hatched, and the survival rate of postlarvae was 20-30%.
This rate was similar to survival rates of postlarvae hatched fromthe egg-bearing females cultured at 3°e. This method of controlling the temperature was more energy-efficient than keeping it at
3°e in summer, and hatching could be advanced by 2 months.
Therefore, the same tank could be used twice or three times toculture larvae. The first mass-cultivation was conducted with eggbearing females cultured at 3-6-8°C. The second group of larvae
hatched from the egg-bearing females cultured at 3°e or caught
in the field.

Survival rate in the air
The survival rate of the eggs at E-250 in the air (100% humidity)
was conducted at -1,3,8, and l3 e (Fig. 6). They survived forover 10 days at -I and 3°e, but 50% died 32 hours later at 8°e.
0

28

w.r.
t"c )
18
13

8

3

-1.8

A
3

2

6

5

4

18

'I (I (

~

13

~

8

3

-1.8

Figure 5
B

5

4

3

2

90
70
50
30
10

6 (days)

Effect of water temperature on the hatchingrate of eggs, 13 to 19 March. (A) Normal
hatching at 31 March and 13-19 March; (B)normal hatching at 17 March.

ratio

TLM

(%)

( hrsl

100 I
I
I
I
I

50

I
I

,,
,

I

\

W.T. (C)

\
\

40

\

10""

",

32 -

• • •

'.
"'" ,

24 ,...
16 I-

"

'.

o

81I

-I

I

I

3

8

•

"--",,-----. L_.

1 ---l.---JL----'-----'-.--J'
L--....L1_.L...-....L...--1_....L...-_...........

(days) 0150
month 4 5 6 7 8 9 10 II
day 21 18 15 20 21 25 1721

I

13

W.T. (tl

300
12 I
18 23

Figure 6

Figure 7

Effect of exposure to air (100% humidity) on the survival rateof eggs at 250 days after spawning.

Egg development reared at 8-6-3°C; (a) egg clutch volumes, (b) volumes of yolk,
compared with (c) standard development.

29

Larvae and postlarvae_
100

Survival and growth rate
The experiment to determine the effect of water temperature on
the survival and growth rate was conducted in polyethylene tanks(47x30x20 cm depth) with 5 liters seawater at -1.8,3, 8, 13,
and 18°C. Four tanks were used for each temperature: two tankswith 20 zoeae and the other two tanks with 40 zoeae. When 50%of the zoea developed to the next stage, the former stage wasregarded as terminated.
The survival rates at Z and G at 8 and 13°C were higher thanthose at 3 and 18°C (Fig. 8). The glaucothoe molted to C-l at 8
and l3°C, but all glaucothoe at 3 and 18°C died before molting
to C-1. The survival rate from Z-I to C-l was 25 % at 8°(: and5% at l3°C. It took 40 days from Z-I to Z-2 at -1.8°C, and all
zoeae died before molting to Z-3.
The relationship between the time (days) of each stage and watertemperature could be expressed by the formula logy=blogx+a(y=time (days) and x= water temperature (0C» with a high correlation (Fig. 9). The variable b was roughly equal to 1; therefore,
these regression formulas were regarded as "the total integrated
temperature" (xy= C) which was approximately 350°C days at Z.

z,

Z2

~

•c

10

G
15

Figure 8

Carapace length at young crab stage

Effect of water temperature on survival rate (%) of larvae.

The relationship between water temperature and growth rate ofyoung king crabs in some reports (Kurata 1961, Nakanishi et al.
1974, Omi 1976 and 1977 in Omi 1980) gave the formulalogy=a+bx (y=carapace length (mm) and x=stage) with a highcorrelation (Fig. 10). I replaced these regression formulas with thehighest value of b (in other words, with the highest growth rateduring each stage) (Table I). The environmental conditions pro-ducing these results were shown from the highest value of b as
follows: more than C-4 at 8-9°C > less than C-5 at 8-9°C > morethan C-4 at 3°C. The growth rate was higher for higher watertemperature and older crabs.

(Days)

100
80
60
40

logY = -0.9697 logX + 5.7439(r = -0.9794)
logY = -0.9369 logX + 5.3504(r = -0.9946)
logY = -0.8275 loqX + 4.6506(r = -0.9779)

20

10
8

logY = -0.9601 l09X + 4.4189(r = -0.9974)(without 0.02 'C)

0.01

20

W.T.

0.1

6

8

10

15 20

Figure 9
Relationship between water temperature and growth rate (days) of larvae.

30

W. T.

('C)

From E-20, E-loo, and E-2oo, oxygen consumption (VO z) increased, but VOz at E-2oo and E-3oo was the same. Oxygen
consumption at 13°C was the highest, the lowest was at 3°C, andthe intermediate at 8°C. Oxygen consumption at Z-l was about ten
times that at E, and from Z-l to C-I at 3°C was almost the same.
Oxygen consumption at Z-3 peaked at 8°C and then decreased fromthis stage.

Oxygen consumption
Oxygen consumption at E-20, E-loo, E-200, and E-3oo, Z, G, andC-I was measured at 3,8, and 13°C (Fig. II). The specimens wereplaced in syringes held in a temperature-controlled water bath. Twowater samples (about 0.2 mL each) were taken from the syringe
at zero time, and two more samples from 30 minutes to 4 hours
later depending on the temperature and the developmental stage.
Oxygen concentration was calculated from oxygen pressure measured by an oxygen meter (Instrumentation Laboratory Co.). Fivesyringes were used, each containing 20-100 eggs or a single larva.

Food consumption
Experiments to determine the effect of water temperature on thenumber of brine shrimp nauplii eaten was conducted at -1.8, 3,
8, 13, and 18°C from Z-I to C-l (Fig. 12). Larvae were put intoa petri dish with 100 brine shrimp nauplii in 30 mL of seawater,
and the number eaten was counted under a stereoscopic microscope
24 hours later. The number eaten at Z gradually increased withthe developmental stage and the increase in water temperature, but
its increase at Z-4 stopped at 8°C. The number eaten decreased
sharply at G and C-I. Perhaps brine shrimp are not a good preyfor postlarvae, since in other experiments with five kinds of foodat G, no food could be found in their stomachs. Perhaps the G does
not feed.

C. L.
(mm)
X

10 l918 l-

•

X

•

7 l-

51-

C

(!)

413 I~

2 I-

~
I-

~ &

•9X

0

0

A

A

i

C

0

C

0

A

0

A

A

0

Cl
Cl

@~

0

Cl

(!)

<!J<

61-

@
@

Movement and activity at young crab stage
When seedlings are released into the field, they are exposed to conditions of rapidly changing temperature. Therefore, the effect ofwater temperature on the movement at C was studied in an experimental tank (180 x40 x40 cm depth) that had six partition walls
inside the tank to make a wide water-temperature gradient. Warm
(16.5°C) and cold (3°C) seawater was put into each corner ofthis
tank (Fig. 13-B). Young crabs at C-4 or C-5 cultured at 3,8, and13°C were released into the tank at 3,8, and 13°C, respectively.
The movements of these crabs were observed for 15 minutes at intervals of 30 seconds. In each experimental condition, five crabs
were used.
The young crabs that were cultured at 3°C and released at 13°C
moved the longest distance 15 minutes after their release (Table
2A). Crabs cultured at 3°C and released at 8°C moved an intermediate distance. The difference between distances moved at 3 and
8°C was large. Young crabs cultured at 13°C and released at 3°C
could not move, and seemed paralyzed. Those released at 8 or 13°C
moved actively. They had no tendency to move to the same watertemperature where they had been cultured, but they distributed
themselves throughout locations of various temperatures (Table 2B).

A

A

II-

0.1 L..-_L-1---,-_,,---1---,-_,,--1_,,--1---,-1_-,-1_-,-1_-,-1_-,1

2

3

4

5

6

7

8

9

10

II

Stage
Figure 10
Relationship between stage and carapace length (CL mm) of young king crab.
• (water temp. 8 DC); 0 (water temp. 3°C); O· x (Omi 1980); 6· D (Kurata1961).

Table 1
Relationship between stage and carapace length of each experiment [log (CL=a+b(STAGEllj. Asterisks indicate p=O.OS.
No.
1
2
3
4
5
6
7
8
9
10

Experiment

Stage

(DC)

Omi 1980
Omi 1980
Nakanishi et al. 1974
Omi 1980

>=C5
>=C5
C8-12
CI-3
=<C4
=<C4

8.0
9.2
9.2
11.4
9.2
8.0

CS-IO
<C8

3.0
9.0
13-17

Kurata 1961
Omi 1980
Kurata 1961

2
0
0

*
*
*
*
*
*
*
*

*
*
*
*
*
*
*
*

*
*

4

5

6

7

8

9

10

b

*

*
*
*
*
*
*
*
*
*

*
*
*
*
*

*
*
*
*
0*

*
*
*
*
0*

0
0

0

*
*

*
*

*
*
*
*
*
*
*
*
*

*
*
*
*
*
*
*
*
*

0.12360.10540.0991
0.09500.08790.07820.07780.07330.05700.0523

0
0

0

*
*
*
*
*
*
31

*
*
*
*
*
*

0

*
*

02com./(.,I/ind)

//

1.0,

I,
I

0.5 ~

Figure 11
Effect of water temperature on oxygen consumption CJ;Llh per individual) at egg, larval, and posUarval stage. Days post-spawning:
Egg I, 20 days; Egg 2, 100 days; Egg 3, 200 days; and Egg 4, 300 days.

I 11 I ~I I] B @J
I I @] @]I
I

11 B ~ ~I~rol
L~ @] -@J

G

Z4

Z3

18

13

8

3

-1.8

Z2

Figure 12
Effect of water temperature on the numbers of brine shrimp nauplii (individuals) eaten by larvae and posUarvae. (Right) birds-eye view of three-dimensionalgraph (left); denser lines indicate high values in the upper graphs.

ourFigure 13
Apparatus to determine the effect of temperature on the movements of young crab. (Aa) warm seawater (16.5°C) flow; (Ab)cold seawater (3°C) flow; (T) thermometer; (B) one example ofwater temperature in the experimental tank.

32

Effect of salinity - - - - - - - - - - -Table 2A
Mean and standard deviation (SD) of the total movement (em) of young kingcrab for 15 minutes in an experimental tank.

The effect of water temperature and salinity on survival rate wasstudied. Eggs that would hatch in about 30 days, Z-I and Z-2, Z~3
and Z-4, G and C-I, were used in this experiment (Fig. 14). Ten
eggs or ten larvae were placed in a I-liter beaker, and the survival
rate after 24 and 48 hours observed. The experimental temperatures
were -1.8,3,8,13,18, and 23°C, and at II salinity conditions
ranging from 0 to 67, at intervals of 6.7. There were 6 x 11 =66
experiments with paired observations. In Figure 14, the area
representing the 100% survival rate at 48 hours was shown fromthe largest area as follows: Z-I and Z-2 > Z-3 and Z-4 > G =eggs (about 30 days before hatching) > C~ I. The tolerance to thechange of water temperature and salinity is the highest at Z, and
it is the lowest at C. The thermal tolerance in 33.5 seawater (ap~proximately the same salinity as natural seawater) was between-1.8° and 18°C. The eggs, larvae, and postlarvae have a large
short-term thermal tolerance.

Rearing water temperature before experiment

x

x

n

SO

29.3 13.00 5
30.2 24.03 5
31.7 16.48 4

3°C
8°C
l3°C

13°C

8°C

3°C
Water temperature(young erab put in)nSO

16.5 7.68 5
43.8 26.37 5
63.5 30.01 4

x

SO

n

3.7 3.32 5
30.2 24.03 5
36.3 18.57 4

Table 2B
Water temperature (OC) occupied by young king crabs 15 minutes after releasein a temperature gradient.
Rearing water temperature before

Effect of hypoxia
on oxygen consumption

experiment
Water temperature(young crab released)

8°C

3°C

l3°C

3.8
4.0
4.0

3.5
4.0

3.9
4.0
3.0

3.6
3.1

3.0
3.0

3.0
3.0

8°C

9.8
8.4
8.1

16.3
8.7

7.6
15.3
2.7

4.8
7.5

9.0
8.4
4.5

9.0
5.0

13°C

9.2
13.9
12.0

11.5
14.0

14.5
15.0
16.1

16.5
16.5

12.9
7.9

7.1
15.5

3°C

T~e same methods used in the experiment on oxygen ~onsumption(VO z) were used to study the effect of hypoxia on VOz at 3, 8,
and 13°C (Fig. 15). Different degrees of oxygen saturation (Paz)were obtained by passing nitrogen gas through seawater. At 3°C,
value for paz where VOz was maintained at a level similar topaz of 90-100% wa.s the lowest at E~ 100 and the highest at G.
The normal rate of VOz at lower paz suggested that there might
be a physiological adjustment for taking up oxygen. A homeostasisof oxygen consumption at E was observed at oxygen saturation
higher than 50 %, and homeostasis of oxygen consumption at Z,
G, and C~ I was observed at paz of 70-80 %, but the gradient at
C-I was above those at Z and G. The effect of water temperatureon oxygen consumption under hypoxia conditions had the sametendency except at G at 3°C.

Discussion

..

)

670
53.6
40.2
26.8

CI

,
I

I
I

",

+

"'-.-----/-t_

These results suggest that there is little negative effect of 8°C
seawater on eggs until the zoea egg stage (about 200 days after
spawning at 3°C), and that 8°C water increases growth rate of eggs
and reduces the rearing cost (Fig. 16). However, from the zoea
egg stage, a temperature of 8°C affected the survival rate, and 3°C
was the optimum water temperature.
The zoeae had a large thermal tolerance, but from the viewpointof growth rate and survival rate, 8°C was the optimum watertemperature. Glaucothoe had the same characteristics. The thcr~
mal tolerance at C was smaller than that of the larvae, and the growthrate suggested that an optimum water temperature for the cultiva~tion was 8°C. The thermal tolerance of king crab was greater thanthat of Hanasaki crab (Nakanishi 1981), and the optimum temperature was lower than that of snow crab (Kon 1980). It seemedthat this characteristic might be one reason for the limitation of themain distribution of the king crab to more northern parts of Japan
than that of the snow crab.

S.l.
(~

_

G

.........~--

13.4

o "---1-'-.8 -...1.3--'8--13'---18'----2.Y3 e99
W. T. I'C)

Figure 14
Effect of salinity (SL) and water temperature on the survival rate of egg, larval,
and postlarval stages.

33

rate

-F:::;t::::;:t:::::;:r=J~

1.0

I

C.l

I

G.

I
I

05i

_IJ~-----,-------:,

95

Z. 2-3
Z.l
Egg4
993
Egg2
9'::5--'--.L-6=-'::5--L-.L-=,-::-L--'-~5
Egg 1
O 2 (%),,---~--r

65

65

95

35

C.1
G.
Z.2-3

Z.1
Egg4

Egg3
Egg2

o

50

100

o

°2(%)

B-2

Figure 15
Effects of hypoxia on oxygen consumption at egg, larval, and postlarval stages. (Lower) birds-eye view of upper three-dimensional graphs; denser lines indicate higher
values in the the upper graphs. Egg I, 20 days; Egg 2, 100 days; Egg 3, 200 days; and Egg 4, 300 days after spawning.

23
18

~
~

13

8
3

-2

Stage E I

E2

E3

E4

ZI

Z2

Z3

Z4

G

CI

Figure 16
Optimum water temperature for egg, larval, and postlarval stages. (1) Survival rate at 48 hours is 100%; (2) survival rate at 30 days at the egg stage is 100%,and juvenile can molt to the next stage; (3) normal cultivation is possible; (4) optimum temperature for mass-cultivation.

34

Acknowledgment_

I wish to express my thanks to Mrs. Naganuma for preparing thefigures.

CitationsKaai, T.
1940. The culture of young crab of the king crab. Hokkusui-shi Junpo 469:3-4(in Jpn.).
Kon, T.
1980. Studies on the life history of the zuwai crab, (Chionoecetes opilio) (0.
Fabricius). Spec. Pub!. Sado Mar. Bio!. Stn. Niigata Univ. 2: 1-64 (in Jpn.,
Eng!. summ.).
Kurata, H.
1959. Studies on the larva and post-larva of Paralithodes camtschatica. I. Rearing of the larvae with special reference to the food of the zoea. Bull. HokkaidoReg. Fish. Res. Lab. 20:76-83 (in Jpn., Eng!. summ.).
1961. Studies on the larva and post-larva of Paralithodes camtschatica. 4.
Growth of the post-larva. J. Hokkaido Fish. Exp. Stn. 18:1-9 (in Jpn., Eng!.
summ.).
Nakanishi, T.
1976. Rearing larvae and post-larvae of the king crab (Paralithodes camtschatical. Proc. FAO Tech. Conf. on Aquaculture, Kyoto, Japan.
1981. The effect of temperature on growth, survival and oxygen consumptionof larvae and post-larvae of Paralithodes brevipes (Decapoda;Anomura). Bull.
Jpn. Sea Reg. Fish. Res. Lab. 32:49-56.
Nakanishi, T., Y. Kuwatani, and H. Kahata.
1974. The relationship between carapace length and body weight of the larva
and post-larva of Paralithodes camtschatica. Bull. Hokkaido Reg. Fish. Res.
Lab. 40:32-37 (in Jpn., Eng!. summ.).
Nakanishi, T., and M. Naryu.
1981. Some aspects of large-scale rearing of larvae and post-larvae of the kingcrab (Paralithades camtschatica). Bull. Jpn. Sea Reg. Fish. Res. Lab. 32:39-47.
Ogata, T.
1974. The studies on the resources ofZuwai crab (Chionoecetes opilio) in Japan
Sea. Nippon-Suisansigenhogo-Kyokai Tech. Rep. 26, 66 p. (in Jpn.).
Omi, H.
1980. Report on the experiment of aquaculture of king crab, 1975-1979.
Tarabagani-zousyokugi jyutu-kaihatushiken-houkoku, 64 p. (in. Jpn.).
Sato, S.
1958. Studies on larval development and fishery biology of king crab,
Paralithodes camtschatica (Tilesius). Bull. Hokkaido Reg. Fish. Res. Lab.
17: 1-102 (in Jpn., Eng!. summ.).

35

It was more than 20 years ago that we heard "toru gyogyo kara
tsukuru gyogyo e" (from the hunting to the cultured fishing). At
that time, Japan was eager to increase maricultured products suchas sea algae (Porphyra tenera), oyster, pearl oyster, and yellowtail.
Thus, techniques that would increase such production, related toenvironmental control, have been expected to be developed. An
example is increasing seawater exchange to improve the water
quality of a farming area in a bay.
Fisheries engineering must concern itself, in the short- or longterm, with the life cycle of marine organisms, from "womb totomb." It must also be interested in favorable conditions for marine
life and dispersion processes of larvae. Engineering problems canbe divided as follows: responses of the animals to the physiochemical environment, dispersion control, imprdvement of water quality,
improvement and construction of habitats, and aquacultural facilities.
This paper reviews some of the methods that can control theaquatic environment as it is related to aquaculture.

Some methods of water-flow
control for mariculture
TOSHIFUMI NOMA
Aquacultural Engineering Division
National Research Institute of Fisheries Engineering
Ebidai. Hasaki-machi
Ibaraki Mz. 314-04 Japan

Water quality control_

To rear a marine organism, the existence of seawater is inevitable;
however, its mere existence is not sufficient for the life of theorganism. Seawater must have a motion that results in an exchangeof the seawater for food or nutritious salts, a supply of dissolved
oxygen, or removal of animal wastes. Energy such as tidal force,sea current, wave, or in some cases, motor power, is needed toprovide proper motion of the seawater.

Improvement of tidal inlets
In Japan, to avoid damage from storm surges, mariculture is performed in a bay well closed by topography. This can result in thedeterioration of water quality because of deficiency in seawater interchange. If there is a tidal motion, a less opened basin causes a waterlevel difference or phase difference of tidal level between the outersea and the inner basin, due to the flow resistance of bottom andside friction of the inlet.
Interchange flow rate q between two waters is expressed byq =± CA y2g!:J.h

C = [1.4 + 0.02 lID413j-1/2

(I)
(2)

where A = cross-sectional area of flow, I!.h = water level difference, I,D = length and depth of the inlet, and g = gravitational
acceleration. Coefficient of discharge, C, depends on length andshape of the inlet. Changes in the tidal inlet may result in improvement of C. This depends on reducing the length and revising thewater depth, D, of the inlet.
Interchange flow, Qmax, can be obtained graphically with tidal
ranges of outer sea and inner basin, ~, (, surface area of innerbasin, S, tidal period, T, and river flow rate, q, (Nakamura and
Hagino 1977).

37

Qmax

ACg

TQr/SsI'"00.5
0
0

G: O

~

:----..
0.5

I'-

~

1.0
1.5

"
"""

...02 . 0...0~...........

0.5

0Q.1

"\.

~

r-....~--...........

\ "I'-.

1\'\ 1\
1'\ f\

\

\

1\

\

-

1\

""

.~

1\

2.5

"1\

1\

"\. 1\

10.0

0.5

50

(ASCY

gr IIII

I Tq r/Ss

-

0.0

1

0.1

0.5

1.0

Outer lTidal~
sea inles Inner basin
River

t

Q~x

S

-qr-

C
T~
1
j

2.5

\1

1

10

\1.0

---- --

r-- i'\t-

\

3.0

1

5

\

\

1\ \~.O

\

2.5

~

1\

\

~ ~

~

'"

1.0

1\

i'-.

--- 0.1--...........

:::::: ~I-"'"
0.05

0.0

1

~

I--"

discharge~0.0-5,.0

outer sea

tidal inlet

inner sea~~':

tidal range
Qmax : maximum flow rate
T : tidal periodA : cross-sectional
area of the flow
C : coefficient of
disctarge

S :tidal range
surface area

Figure 1
Maximum interchange now rate.

Interchange by internal tideIn stratified liquid, there can be an internal wave. When an internal
wave has a period comparable to a tidal period, it is called an internal tide. The propagating velocity of a long wave of an internal
tide is so small that a resonance happens in a bay that has a length
ofless than 10 Ian. Propagating velocity of an internal tide, C, andsurface tide, Cs' are expressed by

x=o

x=a

x

I

AtsL

~~====3=====:::t-P
ITh

T , '"~

Ul

1..,j -s
L_~-::':'----,-lRr--t --.~U
f
(_.
A

(3)

L

-

-

-

+1

(4)
P2 -

PI

E=---

(5)

P2

range at t he bay mout hinternal tidal range

where h = layer thickness, P = water density, and suffix 1 and2 represent the quantities of upper and lower layer, respectively.
A nondimensional density difference, E, has an order of less thanom, soul(6)tidal flow velocity without
internal tide
Figure 2

Symbols and synoptic presentation of nows due to internal tide.

that causes the resonance in bays with short lengths (Nakamura and
Hagino 1980). The resonance results in increased wave amplitude,
so there can be a large amplitude of internal tide. A large amplitude38

of tide induces a large flow velocity in the bay. Flow rates of upper and lower layers ql and q2 are calculated by,. (2n-I)nTl x

sm2aT
ql = 4asinat(2n-I)TI

cos(2n-l)nTI
2T
(7)

.
sm

A2
(2m-I)T2

cos(2m-I)nT~1
2aT(2m-I)nT2
2T. (2m-I)nT~sm
q2 = (2m-I)T2

(8)

2aT

4aA2sinatcos(2m-I)nT2
2T

and the velocities by,
(9)

(10)

and

2n
a =T
4a

4a
T2 = - - - c2(2m-I)

(11)

(12)

where a = length of the bay, T = period of internal tide, A2 , Al
= amplitudes of internal tide and surface tide at the bay mouth,t = time, and m,n = modes of internal and surface tide. T1 meansa proper oscillation period of the bay by surface tidal wave, andT2 , by internal tide. For example, in Norni Bay at Kochi, 20 m
deep, 4 Ian long, the calculated u' by surface tidal range in Figure
2 was about 1 cm/s, but observed upper and lower layer velocities
were about 20 crn/s, and they are compatible with the equations.
This is a phenomenon accompanied by the internal tide. For application, Le., locating and setting of the maricultural facilities, thisphenomenon should be considered.

39

Tidal current control by training wall
The training wall, being located in reciprocal tidal currents where
the flow energy is sufficient, can control flows (Nakamura et al.
1976). On an inlet where the training walls are located, the coefficient of discharge, C, is changed by flow conditions; the differenceof C induces the tidal residual reciprocal flow. Coefficient ofdischarge, Cn , of the defined normal flow, downward in Figure
3, is larger than Ci , upward.
Flow rate is generally expressed by equation (1), the flow rate
in normal flow, qn, becomes larger than the inverse one, qi' Thatcauses the flow path at flood tide in Figure 4 to be larger than thatat ebb tide.

ill! inverse
lliE flow"+ ,I'" \ IIII(\\ I ( '

,
I

\

I

\
\

I

Utilization of wave energy for maricultureI

ifJi
ili asymptote

In deep water, the motion of seawater is circular due to wave action. In a shallow sea, its orbital motion is deformed due to thefriction of the sea floor. As the wave nears shore, its height becomeslarger and a water particle is transported in the propagating direction (shoaling). Shoaling can be used to raise the mean water level
and to induce the water flow (Nakamura and Noma 1977).
Concentrated by the configuration of the intake channel, a wave
travels to the upper end of the slope and over the level beyond.
The flow rate is related to the configuration of the inlet and theincident wave. Noma (1982) reported the design detail and thedeployed example at Taneichi.

II~

*Jl!

VIE

Figure 3
Configuration of training wall.

Sea water exchange
exmtrol by training L......+,.6
wall.-.-,..,..........- -Sea water exchange
control by turnplate

Figure 4
Tidal current control by training wall.

40\

normalflow

Overtopping

Suppression to backwash
by vertical contraction~__ :':'. T ,1\

~
[/
---..

__

......

~.,

I

II

( r\

~---

/fT\

~n?----

Differentiation of flow
coefficient by plane contraction

Differentiation of flow
coefficient at orifice

Figure 5
Mean water level raised by wave energy.

Destratification by air bubble curtain (ABC)
II

II

III

It is desirable that maricultural waters have no thermal or density
stratification for the sake of water quality conservation. To improve
the water quality by destratification, ABC is one of the methods
used with mechanical power. The flow pattern by ABC is as follows.
The lifted water from the lower layer with greater density entrains
the upper layer water, falls down to an appropriate density layer,
and forms a third layer that flows away from ABC. Another upperand lower layer move toward the ABC. When the third layer collides with the end wall in a basin, it is divided into two ways, upperand lower, and they form another upper and lower layer. Thus theupper layer decreases in thickness and the lower increases (Noma1980).
Destratification by ABC may be defined as a change of the thickness of the upper or lower layers, and a change of density of thelower layer. Its terminal phase is that the lower layer reaches tothe surface and the density difference diminishes.
The change of lower layer thickness is expressed by

III

(13)

where Qa = flow rate of supplying air, t = time, and {3 = coefficient of experiment ({3 = 0.125).

Figure 6
Wave energy concentration and breaking of wave.

41

Dispersion control
before operation I under operation

Marine organisms spend their early larval stage floating, and thelarvae are wholly transferred by the motion of seawater. This may
result in a wider distribution of the species, and on the other hand,
may result in a critically high mortality rate at that stage. Dispersion control aims to limit the motion of seawater, including the larvaeof target species, to stay in the planned area. At the same time,seawater should not be stagnant, it is expected to circulate, but toremain in an area. Circulation can be independent of a general flow
and can prevent dispersion.

L

hI

h

he

'V

-~

ha h

U

PI

:Y ~{q,lPI = PI•• , - - r.'"'---------./"'- P?

"/PIII,A. H.C.

J

_

PII

/

I this part is not

Wave-induced circulation

destratifiedql

In a sea with waves, the alignment of a submerged dike induces
circulation. The mechanism is as follows. On the submerged dike,a water particle is transported in the propagating direction by shoaling, it flows back through the portion where there is no submerged
dike, i.e., deeper waters, and that makes a circulation. Intensityof the circulation depends on incident wave height, transmitted wave
height, wave period, water depth, water depth on the dike, and coefficient of frictional resistance (Toda and Nakamura 1981). The flow
velocity along the stream line around the submerged dike is principally calculated byentrainment rate~rom upper layer

Figure 7
Synoptic presentation of the destratification by ABC.

1 2/ 3
u=-h
n

(Mil)

1/2

(14)

(15)

where MI = water level difference by wave set-up, h = water depth,
I = length of the stream line, hd = water depth on the dike, n =Manning's coefficient of roughness, Sf' ST = radiated stresses by
waves in front of and behind the dike, and W o = unit weight ofseawater.

general flow

Figure 8
Synoptic presentation of wave-induced circulation.

42

t%2 63nysec windwave

H~ =44 em

T Y3 =8.2seesea currento/dir. :SE

D
'-

..
(J

water depth

h = 18 cm

flow velocity= 2.9 cm/s
h d = :3 cm
Udepth on the dike
wave
flow

H

5 cm

T

1.2 s

"',0 () a8from left to right

Figure 9

Figure 10

Wave-induced circulation under uniform flow in test basin.

Field investigation of wave-induced circulation by drifting buoys.

Dye concentration in a wake
Behind a submerged structure under uniform flow, there exists a
wake. Dimensional analysis of the wake has been performed. The
size of the wake has been determined; the height is I. 6 X barrierheight, and the length is 10-15 x barrier height. In a wake, there
is a circulation that can detain dissolved substances. Changes inconcentration of such substances can represent larvae, and they correspond well with the velocity field. The area behind the barrier
is classified into three regions (Toda 1982, 1983):
Region I: region of potential flow, where the mean velocity isstrong and turbulence is small; the dye transport, for example, ismainly done by advection.
Region II: intermediate region between I and ill, where the vortex
generated at the edge of the barrier passes.
Region ill: region of the wake, where the mean velocity is weak
and turbulence is large; the dye transport is mainly done bydiffusion.

e -at

u

t - - L'mh--~height and 1/Jidth of thebarrier

The dye concentration change in the wake is expressed byC

region I

h
kU=-U
h-hb

(16)

Q

exchange flow rateL

length of tre VTcl.ke
Figure 11

Definition sketch of the substance exchange behind wall.

where C = the dye concentration at t=t, Co = the initial dye concentration, a = diffusion coefficient. For example, water depth
h = 5 m, barrier height h B = 1 m, flow velocity U = 0.3 mis,a in this case is experimentally given 0.0056. The detention timethat the dye concentration ratio CICo becomes 10% is 411 seconds;
on the other hand, if there is no barrier, the transit time of dye
through 10 times the barrier height is 33 seconds.

43

Conclusions

l.°r.~

height frombottomThe above-mentioned methods are being adopted in coastal fisherygrounds in Japan. Selection of the methods, from the viewpointof the engineer, should be considered in terms of quantity and qualityof energy. Energy sources in coastal water include tides, ocean currents, waves, internal waves, and wind. The quantity and qualityof energy differ from site to site due to topography. The topographical condition and existing energy sources must be examined
before adoption of any method.

60 ~m

"'
0.0

s::
o

oM
.p

co

--=--...,------__..: 00
200

Jrt
D.D

~

.p

o

·jO emll----=~......._----_+_,
o
:00
200

s::

1.:1

CJ

"'IOO~yfi\,
__
-~-_~

OJ

s::
o
t>

OJ

:>

I

>om

+-I-='----~--+-----'==~......o
100

200

::J

,A
'm
oJL~~
o

100

_

Nakamura, M., and S. Hagino.
1977. Study on the sea water interchange. Bull. Nat. Res. Inst. Agric. Eng.
15:99-109.
1980. Study on sea water exchange by internal tide. Bull. Nat. Res. Inst. Fish.
Eng. 1:\-7.
Nakamura, M., S. Hagino, and T. Noma.
1976. Study on the tidal current control for water quality improvement and application of its measure to Seto Inland Sea. Bull. Nat. Res. Inst. Agric. Eng.
14:201-221.
Nakamura, M., and T. Noma.
1977. Study of the induced inlet flow by the concentrated wave. Bull. Nat. Res.
Inst. Agric. Eng. \5:87-98.
Noma, T.
1980. On air bubble curtain (A.B.C.) as a water quality improving method. Bull.
Nat. Res. Inst. Fish. Eng. 1:9-32.
1982. Enhancement of seaweed and sea urchin by utilization of wave energy.
Conference Record, 11th Meeting U.S.-Japan Marine Facilities Panel, p. 28-36.
Toda, S.
1982. On the characteristics of water exchange in the wake. Bull. Nat. Res.
Inst. Fish. Eng. 3: 13-24.
1983. On the characteristics of water exchange in the wake. (IT) Non-<limensional
expression of the coefficient of exchange. Bull. Nat. Res. Inst. Fish. Eng.
4:43-57.
Toda, S., and M. Nakamura.
1981. Experimental study on wave-induced circulation related to offshore structures. Bull. Nat. Res. Inst. Fish. Eng. 2: I-II.

.....
, _ . - -.__
. . c...::=_==p=
! 00
'200

r:! /~
0.0

Citations

20rm

o

oM
.p

_

200

time ( sbaTTier height 20 em
measur:lng point 20 em
from the barrier
Figure 12
Change of dye concentration behind wall at different heights.

44

Production of cultured pearls in Japan dates back to the early 1900s.
The amount of production has increased steadily since the start ofculture, and remarkable development occurred during the 1950s,
with Japanese pearls becoming world famous. Production dropped
rapidly after 1967, however, due to a decrease in demand for pearls.
Production of cultured pearls has been gradualIy rising again since1975 with about 58 tons in 1983 (Fig. I). Japanese fisheries statistics
for 1983 report that pearl production is principally from thesouthwest coast of Japan, in Mie, Ehime, Kumamoto, and Nagasaki
Prefectures (Fig. 2).
As a result oflong-time use of the same areas as culture grounds,
high density of culture, and eutrophication of coastal areas, pearl
farms have been faced with environmental problems which sometimes lead to low productivity of culture areas, decrease in pearl
quality, and mass mortality of cultured oysters. In this review,
general environmental conditions in the pearl culture grounds andsome environmental problems wilI be described. Details of culture
techniques will not be described here, since they are available
elsewhere (Cahn 1949, Kafuku and Ikenoue 1983, Mizumoto 1979).

Environmental conditions
in pearl oyster culture
grounds in Japan
KOVICHIOHWADA I
HARUHIKO UEMOfO
National Research Institute of Aquaculture
Nakatsuhama, Nansei
Mie, 516-01 Japan

Cultured organisms_

Five species of bivalve molIuscs, Pinctada Jucata, P. maxima, P.
margaritifera, Pteria penguin, and Hyriopsis schlegeli, are generally
used in the pearl culture industry. Pinctada Jucata is the species
most commonly used for pearl culture in Japan. The culture techniques which produce spherical pearls have been developed
primarily with this species. Most of the pearl production using
P. maxima is in Australia. This species makes the larger round or120

o~~~m..~,""",m,.I'TT'T'l'TTT'l'TTTT'T'TT1""""'I'TT'I"'rTT'l'"1'T""
1925

35

45

55

65

75

YfJar

Figure 1'Present address: Ocean Research Institule, University of Tokyo, 15-1, I Chome,
Minamidai, Nakano-leu, Tokyo, 164 Japan.

Annual produclion of cultured pearls (Ions) in Japan (from Japanese Ministryof Agriculture, Forestry and Fisheries).

45

half pearls having a maximum diameter of 18 mm and a silverwhite color. P. margaritifera, the' 'black pearl oyster," is mostsuitable for the production of steel black pearls and half pearls.
Pteria penguin, known as "mabe" in Japan, is cultured to obtainlarge-sized half-round pearls. Hyriopsis schlegeli is a freshwater
mussel, and pearl culture with this organism is done in Lake Biwa.

20
10

~

Culture and environmental conditions
required for culture grounds

ton

..£ZL

o

For pearl oyster culture, the hanging method with raft or long line
is most commonly used. Standard size of a raft, which is composedof cypress or cedar logs, is about 6.4 X 5.5 meters, and four floats
are attached underneath the raft. For the long-line method, a ropeis attached to spherical plastic floats. This system, which is stronger
than rafts in rough weather, is used at the entrance or outside abay or inlet. Cages of synthetic netting with vinyl-eoated wire frames
are hung under the raft or the long line.
A year-round process of pearl culture with Pinctada fucata isshown in Figure 3. Natural spawning of pearl oysters begins at atemperature of around 20°C with maximum activity between 22
and 25°C. When collected shells grow to 5-10 mm in shell height,
they are removed from the collector and are placed in baskets for
hanging culture. Young pearl oysters are cultured in cages underrafts for about a year before being sold to pearl cultivators. During
this cultivation period, cleaning of fouling organisms and extermination of the parasite, Polydora ciliata, are necessary to keep
the oysters in good condition. In spring of the third year of life,
the operation of nuclear insertion into the cultured mother shells

0
Figure 2

Distribution of cultured pearl production (tons) by Pref~ctures in 1983 (fromJapanese Ministry of Agriculture, Forestry and Fisheries).

JAN I

I r~AR I APR

FEB

f!JAY

I JUN I JUL I AUG

SEP[~ Natural spawning season---:;:"OCTI NOV I DEC

Raise ITDther shell

IeSettlec.>: spat collection------7

Use ~edar branches as collector

+-'

~

1<

>1

Young pearl oysters are placed in cage

I~

Raise ITDther shell
Maiiltenance

"E

N

o

Cleaning of fouling organismsoExtermination of Polydor~ ciliata

Sale

~

Classify by "",ight and quality

I
I Pearl cultivators purchase7 - 10 tirres a year

the ITDther shells andculture them in cages~"::3' ~at~on at nuclear msert10n

1-

-- -

CuIture in cage

Cleaning of fouling organisms (Hydroides oorvegica,
Harvestingetc.) using high pressure water jet
operationo Extermination of Poll{dora ciliata (inmerse in(small size pearls)
saturated NaCl solutwn)
o Keep away fran water of low oxy:jen concentration andhydrogen sulfideoMaintenanceE'"
I--lWintering)_

Culture>Harvesting operation(large size pearls)

L

+-'
.=r

Figure 3
A year-round process of pearl culture with Pine/ada fUCa/a.

46

begins. Operations are conducted in spring and summer when thewater temperature is above 15°C. During the operation, a nucleus
and a piece of mantle are inserted into a part of the gonad of themother shell. Operated shells are put into cages and cultured again
in the water, under rafts or long lines. It takes 6-8 months for thesmall-sized pearls to be produced by the mother shells. For the larger
sized pearl (6-9 mm in diameter), culture of an additional year isnecessary.
Pinctada fucata is a temperate-zone species. Natural habitat iscoarse sand, gravel, or rock bottom of inner bays, at a depth ofless than 10 meters. Environmental conditions which permit survival of a pearl oyster are of primary importance in the culture
grounds. These conditions are summarized from Kobayashi and
Watabe (1959), Seki (1972), and Uemoto (1981a) as follows:

A
u
:J

300

M

J

A

S

0

N

St. Hl

E
>.

200

L.

U

01

1 00

(Jl

:J..
C
T"

>.
.J::.
0.
.J::.
0.
0

Temperature Basal metabolism of this species increases linearlywith increase in temperature from 13 to 27°C. Above 2rC, it showsa sudden increase in metabolism. Below l3°C the metabolic ratedrops remarkably and hibernation begins. In winter, it is a common practice among growers in the areas where water temperature decreases below l2°C to place oysters in warmer water to keep
their physiological condition normal. Sudden changes in temperature (3-4°C of change during several hours) lead to exhaustionof energy.

0
200
1 00

QJ

ru

.J::.

0....

0
200
, 00

Salinity Salinity of above 18°/00 is required for normal growth.
For the production of pearls of good quality, 21°/00 or higher isnecessary.
e---G

Oxygen Low oxygen concentration itself is not critical to the pearl
oysters. They can tolerate relatively long periods at low oxygen
concentrations, unless the level becomes extremely low (0-1.0mg/L).

0 - 0.5 em- - - 0.5-3.5em()..--() 3.5-&5 em

Current Metabolic rate increases proportionately with increaseof water current up to about 15 cm/sec at a given temperature. Water
current is important for the constant supply of food and oxygen,but a current in excess of 20 cm/sec results in an upset in metabolic
rhythm.

Figure 4
Seasonal changes of phaeophytin contents of muds (J.g/g dry mud) at the threestations in the innermost parts of Ago Bay in 1968 (Uyeno et al. 1970a).

and efforts for their improvement have been studied and summarized by Kusuki (1981).
From 1965 to 1967, when cultured pearl production was highest
in Japan, 48,000 raft units were registered for use in pearl culture
in Ago Bay, the most active culture ground in Japan (Seki 1981).
Assuming that about 5,000 oysters were hung and cultured undera raft unit, then 240 million pearl oysters were estimated to i:'>ecultured in the bay. Average water space occupied by a raft unit
was less than 200 m2 in the innermost part of the bay. In the summer stagnation season, accumulated organic matter and reduced mixing of water led to high consumption of oxygen from the bottom
water and at times even to hydrogen sulfide poisoning. Mass mortalities of cultured pearl oysters occurred at that time (Sawada et al.
1958).
Phaeophytin content of the mud, a degradation product of cWorophyll, is a good indicator of accumulated substances in pearl oyster
grounds (Sawada and Uyeno 1966, Sawada and Taniguchi 1968a,
Uyeno et a!. 1970a) (Fig. 4). Sawada and Taniguchi (1969) andTakimoto (1984) have quantified the degree of deterioration of
sediments using correlations between phaeophytin and organiccarbon content, and between phaeophytin and organic nitrogen,respectively. Sawada and Taniguchi (1969) suggested a reductionof raft numbers in Ago Bay to a level at which one raft unit would

Food The amount of suspended matter required for growth andreproduction of a pearl oyster is estimated to be about 100 grams
dry weight per year. Suspended matter composed mainly of diatoms,
such as Chaetoceros, Thalassionema, Bacteriastrum, Skeletonema,
and Melosira, is preferable for good growth.

Some environmental problems in
the culture grounds

J_

Effect of high-density and repeated culture
Most of the pearl culture grounds in Japan are in relatively enclosed
parts of bays, with a neritic environment. Water circulation in suchareas is not strong enough to remove deposited substances fromthe culture area. High-density pearl oyster culture for long periods
has resulted in accumulation of organic substances in the bottom
muds which mainly consists of dead phytoplankton and faeces. Itoand Imai (1955) reported the decline in productivity of oyster beds
by repeated culture, due to accumulation of organic matter in thesediments and toxic effects of hydrogen sulfide released from thesediments into the water. Deteriorated conditions of oyster beds
47

occupy at least 848 m2 of cultured area, so that normal nutrient
circulation could be continued in the bay.
Through detailed observations of culture area, Uyeno et al.
(1970b) proposed an equation for estimating the bottom fouling asfollows,
12

J
II

Table 1
Estimation of deposited matter and fouling organisms per one raft unit,
holding 100 cages, in a year. Culture period is counted as 245 days from May
to December. Cultured oysters are transferred to another place for hibernation in remaining days of a year (Uemoto 1981b).

12

B =

J +
II

C

1)

(I)

FI2 - Ftl

Average dry weight of deposited matter from culturing pearl oysters:
4.6 g X 100 cages X 245 days = 112.7 kg

2) Average dry weight of deposited matter from fouling organisms on cages:
3.6 g X 100 cages X 245 days = 88.2 kg
3) Average dry weight of deposited matter from fouling organisms on floats:

where

21.2 g X 4 floats X 245 days = 20.8 kgorganic substances accumulated on the surface
of bottom mud from the time t 1 to t2

4) Average dry weight of fouling organisms on cages (cleaning is conducted oncea month):493 g X 100 cages X 8 months = 394.4 kg

amount of effluent organic substances from the
mud surface during t I to t2=

Deposited matter
Fouling organisms
Totalamount of decomposed organic substances inthe superficial bottom mud during t I to t2= amount of organic substances at t I= amount of organic substances at t2.

221.7 kg
394.4 kg
616.1 kg

Table 212f

Amount of deposited matter from one raft unit in a year expressed as cl!emical(COD) and biological (BOD) oxygen demand, organic nitrogen, and organiccarbon.

C can be expressed as follows,

II

f

II

12

C = (Os -0ob)12 .

f

COD
BOD
O-N
O-C
- - - - - - - - - - - (kg) . - - - - - - - - - -(2)
Deposited matter from oysters
Deposited matter from foulingorganisms on cages
Deposited matter from foulingorganisms on floats

where Os= theoretical solubility of oxygen00b
observed oxygen concentrationf = a factor characteristic of the area associated withthe decomposed organic substances between t 1 andt2 represented by phaeophytin.

Total

11.6

3.9

1.2

9.3

5.1

1.0

0.6

4.6

l.l
.17.8

0.4

0.1

0.9

5.3

1.9

14.8

-

Then the following equation can be obtained,
12

12

fA
"

f

II

B = (Os -0ob)12 .

f + Ftl -F '2

Eutrophication of coastal waters(3)

Seki (1981) and Uemoto (l981a) reviewed the present status of
eutrophication of pearl oyster grounds in various localities. They
showed that long-term effects of eutrophication of coastal waters
would gradually appear in the bottom quality, and as changes in
the flora and fauna in the water and sediment, rather than in theapparent nutrient levels in the water. For example, Uemoto (l98Ia)
could not find clear changes in nutrient levels in the water of Ago
and Uwajima Bays from 1959 to 1977. Yamamura (1972), however,observed a succession of marine fouling communities in Ago Bay
between 1958 and 1967 (Table 3). Increasing concentrations of total
sulfide and organic carbon in the sediments of the innermost partof Ago Bay have been observed (Seki 1981) (Fig. 5). Occurrencesof red tides caused by dinoflagellates have been increasing in
Gokasho and Ago Bay areas (Seki 1981) (Fig. 6). Honjo et al. (1984)
observed the virtual disappearance from the water of diatom communities, which are good food for the cultured pearl oyster, forabout a month during June 1984, while Gokasho Bay was attacked
by red tide caused by Gymnodinium nagasakiense.
According to the Environmental Division, Mie Prefecture, total
sewage wastes around the Ago Bay area amounted to about 2 tonsof biological oxygen demand and 0.78 tons of nitrogen per day in
1973, namely 730 tons of biological oxygen demand and 285

Thus if the data on water temperature, salinity, dissolved oxygen,and phaeophytin in the superficial bottom mud are available, thenthe extent of bottom fouling can be ascertained rather easily. It would
then become possible to calculate the optimum number of cultured
pearl oysters per unit area from the viewpoint of water quality andbottom fouling.
Uemoto (1981 b) estimated the amount of deposited matter andfouling organisms per unit of raft in a year in Ago Bay as shownin Table 1 Amount of ~otal deposited matter from cultured pearl
oysters and fouling organisms was estimated to be 221.7 kg in ayear if 100 cages (each cage holding 50 oysters) have been cultured.
The total amount of fouling organisms, which had been removed
hy the cleaning process, was estimated to be 394.4 kg in a year.
Estimation of this amount as chemical and biological oxygen demand, organic nitrogen, and organic carbon is shown in Table 2.
Similar results have also been reported in Uwajima Bay, Ehime
Prefecture (Takimoto 1984). Uemoto (1981b) further estimated thetotal amount of discharge by pearl oyster culture into Ago Bay in1975, assuming that 30,000 units of rafts were used, as 530 tons
as chemical oxygen demand, 160 tons as biological demand, 54
tons as organic nitrogen, and 440 tons as organic carbon.
48

Table 3
Comparison of dominant species of fouling organisms in Ago Bay in summer (July-August) between 1958 and 1967,
modified from Yamamura (1972).
1958*

1967

Species*'INo. per1,600 m2%

Species"INo. per1,600 m2%

Dexiospira foraminosus
Balanus variegatus tesselatus
Dakaria subovoidea

14,214
1,769
694

84.2
10.5
4.1

Hydroides norvegica
Balanus variegatus tesselatus
Musculus senhousia
Dexiospira foraminosus
Balanus improvisus

4,149
2,169
354
313
146

53.2
28.1
4.5
4.0
1.9

16,889

Total

--

7,803

Total

'Data cited from Kawahara and lijima (1960).
"Only dominant species are presented.
ITotal number of individuals attached to the surface of the concrete blocks immersed at four different depths (0, 2, 3.5,
and 5 m).

25

4..-...

-- 3
(Jl

( Jl

E
........
IJ)

20

2

I
~

>. 15
u

1966

0

c

0-.0

~

OJ

OJ'?!

CT

OJ

9)(.....

50

-

...X

;;;,

'-

10

~,'

o I

0/

-- 40 1966
(Jl
( Jl

E
u 30

,,X
I

5

~

I
0

20
1973
J FMAMJ J A

SOND

75

77

79

Figure 6
Occurrence of red tide in Gokasho and Ago Bay areas (Seki 198\).

M on t h
Figure 5
Seasonal changes of total sulfide (ToS) and organic carbon (O-C) contents in thesediment at the innermost part of Ago Bay for different years (Seki 1981).

tural activIties. Among these, utilization for finfish culture has
been most prominent. Discharge of organic material into the surrounding environment from yellowtail culture has been studied by
Sakamoto (1976). He estimated higher organic loading of the surrounding waters by yellowtail culture than by waste discharge fromthe land area. Finfish cultural activities as well as sewage waste
would also contribute to eutrophication of coastal pearl oyster culture
grounds where finfish and pearl oyster culture arc:' located close
together.

tons of nitrogen per year (Demoto 1981 b). Even though all theamount has not been discharged into the bay, the total was significantly higher than the discharge from pearl oyster culture in
the bay.
The coastal enclosed bay areas which used to be mostly utilized
for pearl oyster culture are now used for various other aquacul-

49

Approach to improve deteriorated
bottom quality

1968b. Studies on the underwater blasting of reef in the pearl culture ground(11). IV. On the changes of environment of the pearl culture ground by the underwater blasting. Bull. Nall. Pearl Res. Lab. 13:1703-1711 (in Jpn.).
1969. The oceanographical studies on the pearl culture ground. VI. On the relation berween the raft density in pearl culture ground and the contaminated degreeof bottom mud. Bull. Nall. Pearl Res. Lab. 14: 1719-1734 (in Jpn.).
Sawada, Y., M. Taniguchi, Y. Wakazono, T. Ogawa, and M. Nakano.
1968. Studies on the explosion ploughing of the bottom mud in the superannuated pearl culture ground. Bull. Natl. Pearl Res. Lab. 13: 1241-1247 (inJpn.).
Sawada, Y., and F. Uyeno.
1966. Studies on the acetone extracts from marine mud and faeces of pearl oyster(Pincrtuln manensl). L On the absorption spectra of acetone extracts. Bull. Nall.
Pearl Res. Lab. 11:1298-1307 (in Jpn.).
Seki, M.
1972. Studies on environmental factors for the growth of pearl oyster, Pincrtuln fucara, and the quality of its pearl under the culture condition. Bull. Mie
Prefect. Fish. Exp. Stn. 1:32-149 (in Jpn.).
1981. Present status of eutrophication in pearl culture grounds and their improvement. Bull. Jpn. Soc. Sci. Fish. Oceanogr. 38:38-41 (in Jpn.).
Seki, M., and N. Shibahara.
1967. Effects of sprinkling ferric oxide on the bottom sediments for the improvement of pearl culture ground. Annu. Proj. Rep. Mie Prefect. Fish. Exp. Stn.
for 1965, p. 221-228 (in Jpn.).
Takimoto, S.
1984. Studies on the organic loading into culture farm by pearl oyster culture.
Aquiculture (Sendai) 32:77-82 (in Jpn.). See Suisan Zoshoku (Fish. Cult.).
Vemoto, H.
1981a. Long term changes of nutrient levels and succession of pearl oyster culture
grounds. Bull. Jpn. Soc. Sci. Fish. Oceanogr. 38:28-37 (in Jpn.).
1981b. On the depositing matter in the pearl culture grounds. In The processof settling and sedimentation in bay and coastal region, p. 126-138. Jpn. Fish.
Resour. Conserv. Assoc. (in Jpn.).
Uyeno, F.
1964. Relationships between production of foods and oceanographical condition of sea water in pearl farms. II. On the seasonal changes of sea water constituents and bottom condition, and the effect of bottom cultivation. J. Fac.
Fish. Prefect. Univ. Mie 6: 145-169 (in Jpn.).
Uyeno, F., S. Funahashi, and A. Tsuda.
1970a. Preliminary studies on the relation between faeces of pearl oyster(Pincrtuln manensi) and bottom conditions in an estuarine pearl oyster area.
J. Fac. Fish. Prefect. Univ. Mie 8:113-137 (in Jpn.).
Uyeno, F., K. Kawaguchi, N. Terada, and T. Okada.
I 970b. Decomposition, effluent and deposition of phytoplankton in an estuarine
pearl oyster area. J. Fac. Fish. Prefect. Univ. Mie 7:7-41 (in Jpn.).
Yanlamura, Y.
1972. Ecological studies of marine fouling communities in pearl culture ground.
n. Seasonal changes in the constitution of marine fouling communities at various
depths in Ago Bay. Bull. Natl. Pearl Res. Lab. 16:2038-2051 (in Jpn.).

_

Improvement of deteriorated environmental conditions ca-Jsed by
red tides has been studied by the Fisheries Agency (Fisheries Agency1983). Several attempts have also been made to improve deteriorated
bottom conditions in the enclosed areas of pearl oyster grounds,
such as cultivation (Sawada and Taniguchi 1967, Uyeno 1964) and
explosive ploughing of the sediment (Sawada et al. 1968), underwater blasting of obstacles (Sawada and Taniguchi 1968b), bottom
aeration (Mie Prefect. Fish. Exp. Stn. 1966), and sprinkling ferricoxide on the bottom sediment (Seki and Shibahara 1967). A recent
approach of liming the bottom sediment seems to be successful for
preventing hydrogen sulfide formation in the deteriorated bottom
areas (Nishimura and Seki 1983). The amount of lime required isestimated to be 100-200 grams/m2 .

Citations_

Cahn, A.R.
1949. Pearl culture in Japan. Nat. Resour. Sect. 122, GHQ, 91 p.
Fisheries Agency.
1983. Manual of the projects on developing techniques for protection fromdamage by red tides in mariculture grounds, 51 p. (in Jpn.)_
Honjo, T., K. Ohwada, N. Tanaka, S. Toda, A. Asakawa, and H. Uemoto.
1984. On the red tide causing major damage to cultured fishes and shellfishes
in Gokasho Bay_ Natl. Res_ Inst. Aquacult. news 8:5-9 (in Jpn.).
lto, S., and T. lmai.
1955. Ecology of oyster bed. L On the decline of productivity due to repeatedcultures. Tohoku J. Agric. Res. 5:251-268.
Kafuku, T., and H. lkenoue (eds.).
1983. Modern methods of aquaculture in Japan. Developments in aqJaculture
and fisheries science, vol. II. Elsevier Sci. Publ. Co., 216 p.
Kawamura, T .• and H. Iijima.
1960. On the constitution of marine fouling communities at various depths in
Ago Bay. Rep. Fac. Fish. Mie Univ. 3:582-594.
Kobayashi, S., and T. Watabe.
1959. Studies on Pearls. Gihodo Publisher, 280 p. (in Jpn.).
Kusuki, Y.
1981. Fundamental studies on the deterioration of oyster growing grounds. Bull.
Hiroshima Fish. Exp. Stn. 11:1-93 (in Jpn.).
Mie Prefectural Fisheries Experimental Station.
1966. Effect of aeration of bottom sediment on the improvement of pearl culture
grounds. Annu. Proj. Rep., Mie Prefect. Fish. Exp. Stn. for 1964, p. 144-148(in Jpn.).
Mizumoto, S.
1979. Pearl farming in .Japan. In Pillay, TV. R., and W. A. Dill, (eds.) Advances in Aquaculture, p. 381-385. Fishing News Books, Ltd.
Nishimura, A., and M. Seki.
1983. Effects of lime on the improvement of mariculture grounds. Bull. Jpn.
Soc. Sci. Fish. 49:353-358 (in Jpn.).
Sakamoto, 1.
1976. Assessment of the load caused by pisciculture to the environment. Rep.
Environ. Sci. Mie Univ. I: 181-203 (in Jpn.).
Sawada, Y., M. Tange, and M. Seki.
1958. The oceanographical studies on the pearl culture ground. L On theoceanographical observation of unusual death of pearl oyster at Tategami-ura
in Ago Bay in July 1958. Bull. Nall. Pearl Res. Lab. 4:347-355 (in Jpn.).
Sawada, Y., and M. Taniguchi.
1967. The oceanographical studies on the pearl culture ground. IV. On theseasonal changes of bottom conditions and the improvement method of bottom
mud in the superannuated pearl farm. Bull. Nall. Pearl Res. Lab. 12:1~79·1408(in Jpn.).
1968a. The oceanographical studies on the pearl culture ground. V. On theseasonal changes of organic matter and phaeophytin c"ntents in bott~m mudof the superar;nuated pearl culture ground. Bnll. Natl. Pearl Rts. Lab.
13:1689-1702 (in Jpn.).

50