3* b$d>@?%,

Sci. Rep. Hokkaido Salmon Hatchery, (45): 25-33 (1991)

Seasonal Changes in Seawater Adaptability of the Hatchery Reared

Juvenile Sockeye Salmon, Oncorhynchus nerka

Masatoshi BAN*' and Kohei YAMAUCHI*'

Abstract
Seawater (33%~) challenge test was performed to assess the development of seawater
adaptability in the underyearling and yearling sockeye salmon, Oncorhynchus nerha, from
July, 1989 to July, 1990. The body silvering were observed throughout the experimental
period, whereas the pigmentation of both dorsal and tail fin margins appeared duringfrom July to October, 1989, and from May to June, 1990. A survival rate of 100% was
observed on the 7th d a y after transfer into seawater in August and September 1989, andin May and June, 1990. Serum sodium contents after the 7th day of transfer into seawater
were low in August and September, 1989 and June, 1990. High gill Na+, K+-ATPase
activities were observed in August, 1989 and June, 1990. These results suggest that theunderyearling and yearling sockeye salmon develop seawater adaptability in August andin June, respectively.

Introduction
Smoltification (parr-smolt transformation) in salmonids is a very complex phenomenon
composed of morphological, physiological and behavioral changes ( H o a r 1976, 1988). In general, almost the salmonids smoltify in the river a f t e r hatching o u t , followed by migration tot h e sea. During smoltification, seawater adaptability developes simultaneously with the occurrence of both body silvering and pigmentation of dorsal and caudal fin margins (Kubo 1980 ;Gorbman e t al. 1982 ; Yamauchi e t al. 1984).
Sockeye salmon, Oncorhynchus nerha, display the m o s t varied and complex life histories
within genus 0ncodz.ynchus ; their life patterns a r e classified into three categories : sea-, riverand lake-types (Wood e t al. 1985). However, only the lake-type a m o n g them has been reported
in Japan. Recently, trials f o r the release of lake-type sockeye salmon h a s been performed inorder to produce a new resource of the fish. To improve the survival r a t e of the fish, informations on t h e physiological characteristics including the development of seawater adaptabilitya r e important.

This paper describes the seasonal changes accompanying t h e development ofseawater adaptability in hatchery-reared sockeye salmon.
JL.&iS S M

b $dxlLEj.tiffR%@%
328 7* 'Hokkaido Salmon Hatchery, Fisheries Agency of J a p a n , 2-2 Nakanoshima, Toyohira-ku, Sapporo
062 JAPAN ( H E@: 7k&Edk&S 3 I9 * b$AlL~:r)*2Faculty of Fisheries, Hokkaido Universlty, 3-1-1 Minato, Hakodate 041 JAPAN ( L l l l f 3 @ *7kEW3): jh&gAy

25

Materials and Methods
Fish : Eggs were obtained from adult sockeye salmon, Oncorhynchus nerka, caught in October,1988 from the Abira River, Hokkaido. They were transferred t o Chitose Branch, Hokkaido
Salmon Hatchery and reared in well water indoor ponds(7-8"C). After hatching out in Januaryof 1989, they were raised in outdoor well water ponds (7-8°C) under natural photoperiod until
July of the same year. The fish were transported t o another outdoor pond, and were samples
monthly until July, 1990.
Rearing water temperature and photoperiod during the period
sampled the fish were shown in Fig. 1. Food (dry pellet : Taiyo Jiryo) were supplied twice a
day during the experimental period.

J

A

S

O

c

N

D

J

F

M

-+o

A

M

J

J

I+1990

1989

Month

Fig. 1. Seasonal changes in day length () and watertemperature ( . - - .---.....) from July, 1989 to J u l y , 1990.
Water temperature was expressed as mean values of eachten days.
~

Seawater challenge : To determine seawater adaptability, seawater challenge test were performed (Clarke and Blackburn 1977). 50-100 fish samples collected randomly were transferred
into artificial seawater (33%, 11.O+l.O0C>. On the 1st and 7th day after the transfer, after

anesthetizing using tricaine rnethanesulfonate (MS2221, their fork lengths were measured (Fig.

2). Blood samples were obtained from the caudal vein using a capillary. Gill fillaments wereimmediately rinsed in ice-cold homogenizing solution (250 m M Sucrose, 6 m M EDTA-2Na; 20mM imidazole, pH 6.8) and frozen immersed in the solution (20 times volume) until Na+, K+
PATPase assay. Serum obtained by centrifugation a t 10,000 g for 5 min were stored at -40°C
until sodium content assay.
Serum sodium concentrations : Serum sodium concentrations in freshwater and seawater were
measured using an Atomic Absorption and Flame Emission Spectrometer (Shimadzu, AA-64013).
Na', Kf-ATPase activity : Gill fillaments were homogenated in lmk' of the above solution,
26

Ban and Yamauchi : Seawater Adaptability of Sockeye Salmon

160 'I

h

140

-

120

-

100

-

80

-

E

Y

r,
rn

C

Q)

3

0

OJ
1

.

J

1

A

1

S

1

O

1

N

1

D

1

J

1

F

1

M

1

A

1

M

1

J

1

J

-+1-+0+
1989

1990
MONTH

Fig. 2.

Seasonal changes in fork length of hatchery-reared
sockeye salmon from J u l y , 1989 to J u l y , 1990. The
vertical bars represent the m e a n i S E .

and 40 b(Le of the homogenated was incubated either in 160 ut? of reaction mixture A (250mM imidazole, 12.5 m M ATP2Na, 337.5 m M NaCl, 162.5 m M KC1, 50 mM MgC12) or 160
L L ~of reaction mixture B (reaction mixture A + 2 . 5 mM ouabain) f o r 20 min a t 37°C in ashaking incubator. The reaction was stopped by adding 4 d of iron TCA solution (100 g TCA,
10 g thiourea, 30 g ferrous anmonium sulfate in 1 liter), Free Pi was measured according t o
the method of Goldenberg and Fernandez (1966) and protein concentrations were determinedby the method of Lowry e t al. (1966).
Statistical analysis : The d a t a presented are expressed as m e a n s i S E M . One-way analysis ofvariance followed by the Student-Newman-Keul's multiple range test were conducted.

Results
External appearrance : Throughout the experimental period from June, 1988 t o June, 1990,
body silvering was observed. In contrast, pigmentation on the dorsal fin margins of under-

yearling and yearling fish was observed from July to October (1989) and from May to June
(199O), respectively.
Survival rate in seawater : Survival rate of fish on the 7th day after transfer t o seawater

was determined (Fig. 3). The survival rates in underyearling fish were 100% in August andOctober (1989). Thereafter the r a t e dropped to 33%, in November, followed by low survival
rates until February, 1990. In March, the survival r a t e of the yearling fish increased, andattained 100% in May and June, 1990, followed by dropping t o 51% in July.
Serum sodium contents : Serum sodium contents in underyearling freshwater fish showed

gradually increasing levels : from 1 2 7 . 6 t 5 . 9 mEq/C in July t o 154.9*1.3 mEq/t? in October
27

100

-

h

5 75-

-al

E

.->

50

-

25

-

2

=I

01

1

1

,

1

,

1

1

)

1

,

1

~

Fig.3. Seasonal changes in the survival r a t e on the 7th
d a y after transfer to s e a w a t e r ( 3 3 x 0 ) f r o m J u l y , 1989
to J u l y , 1990.

220

-

200

-

180

-

160

-

=
.
U

4 FW

Y

v)

c
.O

E

I

E

e

8

.-U5 140 0

5 120 v)

z

-

O J
.

J

A

1

S

,

O

,

N

1

D

,

J

,

F

M

,

,

A

,

M

,

J

-+1-+0+
1989

1990

MONTH
Fig. 4.

Seasonal changes i n s e r u m s o d i u m concentrationsof freshwater fish (-1and s e a w a t e r fish (-1o n the 7th d a y after transfer to s e a w a t e r (33x0) f r o m
J u l y , 1989 to J u l y , 1990. The vertical bars represent
the mean-+SE.

~J

Ban and Yamauchi : Seawater Adaptability of Sockeye S a l m o n(19891, followed by fluctuating values between 140.013.4 m E q / t and 155.2k1.1 m E q / luntil May (Fig. 4 ) . In June and July, 1990, the levels dropped again to 136.4+2.7 and 139.3
1 3 . 4 mEq/k, respectively. In contrast, the concentrations of serum sodium in seawater underyearling fish were low in August (165.5+2.2 m E q / t ) and September (169.5k3.1 m E q / t ) ,showing good seawater adaptability, followed by a gradual decrease in adaptability. After thepeaked levels in February (19901, the sodium levels began to decrease, and attained lower value(157.5k1.9 m E q / t ) in June (1990).
In underyearling fish in August, 1989 and yearling fish in June, 1990, time course changes
in serum sodium concentrations were investigated on the 1 s t and 7th day a f t e r transfer t o
seawater (Fig. 5 ) . Serum sodium levels of August underyearling fish in freshwater was 140.9
k 1 . 9 mEq/k. The sodium concentrations increased t o 184.0k3.9 mEqM on the 1st day a f t e rtransfer t o seawater, which decreased t o 165.5+2.2 mEq/k on the 7th day a f t e r transfer t o
seawater. In contrast, serum sodium concentrations in June yearling fish in freshwater showed
136.4k2.7 mEq/k'. The levels on the 1st day after transfer t o seawater increased to 1 6 4 . 6 k
6.3 mEq/t which were lower in comparison with t h a t in August underyearling fish. The sodium
levels on the 7th day after transfer t o seawater showed low levels, 157.5k1.9 mEq/t.
Na+, K+-ATPase activity : In the freshwater fish, gill Na+, K+-ATPase activity peaked inAugust, 1989 (16.6k2.0 umoles Pi/mg pro./hr.) (Fig. 6 ) . Thereafter, the activity decreasedt o 5.5+0.6 umoles Pi/mg pro./hr., and maintained the same levels (5-6 umoles Pi/mg pro./hr.) until April (1990). In June, the activity peaked again ( 1 6 . 3 i 0 . 7 umoles Pi/mg proJhr.1.
On the other hand, the Na+, K+ -ATPase activity in seawater fish showed similar patterns t o

--

FW

200

A

1dinSW

W
Lu

T

0 7dinSW

180
Q)

.-c0

T

L

r

160

0)

'

0

r

.-E,

140

U
0
Q)

E

120

3

%

v)

100

AUG (1989)
O+
Fig. 5.

JUN (1990)

I+

Time course changes i n seruni sodium
concentrations o n the 1st a n d 7th day after
transfer to seawater (33%0) in underyearling(August, 1989) a n d yearling fish ( J u n e ,1990). The vertical bars represent the m e a n
kSE.
29

B

]
0

1

1

J

1

A

,

S

1

O

1

N

1

D

1

J

1

1

F

M

.

A

1

M

1

J

1

J

@
1989

Month

1990

Fig. 6. Seasonal changes in gill N a f , K f - A T P a % activities
in freshwater fish (M)and seawater fish (-1on the 7th d a y after transfer to seawater (33%0). The
vertical bars represent the m e a n k S E .

those of freshwater fish. However, the activity in seawater fish between October (1989) and
April (1990) were relatively higher (10.81kO.6-11.710.5 fimoles P i / m g pro./hr.) than thoseof freshwater fish.

Discussion
In general, salmonids a r e known t o change in external appeamance, such as body silveringand pigmentation of the dorsal and caudal fin margins during smoltification(Hoar 1976,1988).

In the present s t u d y , sockeye salmon showed body silvering throughout the experimental period
during between J u l y (1989) and July (19901, whereas pigmentation of the dorsal and caudal
fin margins was observed f r o m July t o October, 1989, a n d f r o m M a y t o June, 1990. The
occurrence of the pigmentation coincided with the development of seawater adaptability which
will be described in the following discussion. Hence, the pigmentation of dorsal and caudal fin
margins seems to be a good criteria t o determine the development of seawater adaptability insockeye salmon.
Aside f r o m changes in t h e external appearrance, salmonids undergo physiological changes
during smoltification. Among t h e m , seawater adaptability developes during smoltification(Hoar 1988). I t is reported t h a t gill N a f , K+-ATPase

activity increases during smoltifica-tion in coho salmon (Zaugg and Wagner 1973 ; Folmar and Dickhoff 19801, steelhead trout(Zaugg and McLain 1 9 7 1 ) , Atlantic salmon (Boeuf e t al. 1985) and masu salmon (Ban e t
al. 1987a, b). Therefore, gill N a f , K+-ATPase

activity is known t o be one of indicators ofthe development of seawater adaptability in salmonids ( H o a r 1976, 1988). In the present study,
high gill Naf, Kf -ATPase activities were observed in underyearling and yearling fish, coincidedwith the high survival r a t e in seawater. Furthermore, serum sodium concentration on the 7 t h30

Ban and Yamauchi : Seawater Adaptability of Sockeye Salmon

a f t e r transfer to seawater decreased with a concomitant increase in the gill N a f , K+ PATPase
activities.
Furthermore, seawater challenge test is useful t o assess the development of seawater
adaptability in salmonids (Clarke and Blackburn 1977).

In the present study, serum sodium

concentrations which were investigated 7 t h day a f t e r transfer t o seawater decreased in accord
with the increase in gill Na+, K+ -ATPase activities. Therefore, gill N a f , K+ -ATPase activities, a n d serum sodium concentrations a f t e r transfer t o seawater seem t o be good indicatorst o determine the development of seawater adaptability in sockeye salmon as well as in othersalmonids.
The results on the survival r a t e a f t e r transfer t o seawater, seawater challenge test andgill N a f , Kf -ATPase activity suggest t h a t the seawater adaptability develop in both underyearling fish and in yearling fish in August, 1989, and June, 1990, although a d a p t a t i o n toseawater in t h e underyearling fish w a s slightly poorer, compared with t h a t of the yearling
fish. Baggerman (1960) and McInerney (1964) described t h a t seawater preference observed in
the sockeye salmon f r y a f t e r hatching o u t was maintained until June, followed by a decrease,which developed again in May-July of t h e following year. Similarly, in hatchery reared sockeye
salmon, Kaeriyama e t al. (1987) described t h a t yearling fish showed seasonal changes in seawater adaptability. These findings may indicate t h a t the development of seawater adaptability
occur seasonaly in both the underyearling and yearling fish.
Occurrence of smoltification in salmonids including sockeye salmon is judged f r o m t h edevelopment of seawater adaptability and changes in external appearance (Hoar 1976). In
general, a l m o s t all of t h e sockeye salmon smoltify as yearling fish(Mc1nerney 1964 ; Kaeriyama
e t al. 1987 ; Wood e t al. 1987). As described earlier, August underyearling fish as well as June
yearling fish developed seawater adaptability concomitant with the pigmentation of dorsal a n dcaudal fin margins. Since environmental factors affect smoltification (Wedemeyer e t al. 19801,
i t seems likely t h a t hatchery-reared sockeye salmon as underyearling fish smoltify underrearing condition adopted. To ascertain this, f u r t h e r investigations a r e required.
In conclusion, under artificial rearing condition used in the present study, underyearlingsockeye salmon may smoltify as well as yearling fish. This finding may explain the occurrenceof t h e varied and complex life histories in the sockeye salmon.

Acknowledgements
We wish t o express our appreciation t o Dr. Osarnu Hiroi, Hokkaido Salmon Hatchery f o r
encouragement of this study. Thanks also due t o s t a f f of Chitose Branch, Hokkaido Salmon
Hatchery f o r their e f f o r t rearing and supplying the experimental fish. This work was supported
in p a r t by Grant-in-Aid f r o m the Ministry of Education, Science and Culture, and Agriculture,
Forestry and Fisheries Research Council, the Ministry of Agriculture, Forestry and Fisheries,
Japan.

31

References
Raggerman, B. (1960) : Salinity preference, thyroid activity and the seaward migration of four
species of Pacific salmon (Oncorhynchus). J. Fish. Res. Bd. Can.17 (31, 295-332.
Ban, M., K. K a s a h a r a , and K . Yamauchi (1987a) : Physiological changes in the hatchery-reared
yearling m a s u salmon ( Oncorhynchus masou) during smoltification. Sci. Rep. Hokkaido
Fish Hatchery, (42), 27-35. (in Japanese with English abstract)Ban, M., K. K a s a h a r a , and K. Yamauchi (1987h) : Physiological changes i n the hatchery-reared
underyearling masu s a l m o n ( Oncorhynchm masou) during smoltification. Sci. Rep.
Hokkaido Fish Hatchery. (42), 19-26. (in Japanese with English abstract)
Boeuf, G . and P. Prunet (1985): Measurements of gill ( N a + -K+> -ATPase activity and p l a s m a
thyroid hormones during smoltification in Atlantic salmon ( S a l m o salar L.) . Aquaculture,45, 111-119.
Clarke, W . C. and J. Blackhurn (1977) : A seawater challenge test to measure smolting in juvenile
salmon. Fish. Mar. Seru. Tech. R e p . , (7051, 1-11.
F o l m a r , L. C. and W. W . Dickhoff (1980) : The parr-smolt transformation (smoltification) a n dseawater adaptation in salmonids. A Review of selected literature. Aquaculture. 21, 1-37.
Goldenberg, H. and A. Fernandez (1966) : Simplified method for the estimation of inorganic
phosphorus in body fluids. Clin. Chem., 12, 871-882.
G o r b m a n , A., W. W.Dickhoff, J. L.Mighel1, E. F.Prentice, and F. W. Waknitz (1982): Morphological indices of developmental progress i n the parr-smolt coho s a l m o n , Oncorhynchus

kisutch. Aquaculture. 28, 1-19.
H o a r , W . S. (1976) : Smolt transformation : evolution behavior and physiology. J. Fish. Res. Bd.
Can. 33, 1234-1252.
H o a r , W. S. (1988) : The physiology of smolting salmonids. In Fish physiology. (W. S. H o a r and

D. J. R a n dell, ed.), pp. 275-343. Academic press New York.
K a e r i y a m a , M., I. Shimizu, and H . Kakizakl (1987) : Seasonal changes i n seawater adaptation ofsockeye s a l m o n reared in the freshwater. Sci. Rep. Hokkaido Salmon Hatchery, (411,129-135. (in Japanese with English abstract)
Kubo, T. (1980) : Studies on the life history of "Ma su " s a l m o n (Oncorhynchus m a s o d in Hokkaido.

Sci. Rep. Hokkaido S a l m o n Hatchery, (341, 1-95. (in Japanese with English abstract)
Lowry, 0. H., N. J. Rosebrough, A. L. Farr, and R . J. Randall (1951): Protein measurementwith the F o h n phenol reagent. J. Biol. Chem., 193, 265-275.
Mclnerney, J . E. (1964) : Salinity preference : a n orientation mechanism in salmon migration. J.
Fish. Res. Bd. Can., 21 (51, 995-1018.
Wedemeyer, G . A., R . I,. Saunders, and W. C. Clarke (1980) : Environmental factors affecting
smoltification and early m a r i n e survival of a n a d r o m o u s salmonids.

Marine Fisheries

Reuiew. 42 (61, 1-14.
Wood, C. C. and B. E. Riddell, a n d P. T. Rutherford(1985): Alternative juvenile life histories ofsockeye salmon ( Oncorhynchus nerka) and their contributlon to production i n the Stikine
River, Northern British Columbia. p. 12-24. In H. D. Smith, L. Margolis, and C. C. Wood(ed.) Sockeye s a l m o n ( Oncorhynchus nerka) population biology and future management.
32

Ban

Can.
Yamauchi,and: Seawater

Adaptability 0f SOckeye Salmon

Spec. Pub1. Fish. Aquat. Sci., 96.
K., N. KOide, S. Adachi, and Y. Nagahama

and

b100d

thyroxine

chus

mason,

andconcentrations

smolt

transformation

during smoltification

H. I1. Wagner

migration

rature.

COmp.

Of themasu

salmon,(1971): Changes In gill ATPase

activity

gairdneri), coho

tn steelhead trout (Salmo

Oncorhyn‑associated

with

parr‑

salrnon (Oncorhynchus(0. tshawytscha.) J. Fish. Res. Bd. Can.

(1973): Gill ATPase

adaptability

rhodu.rus. Aquaculture, 42, 256‑274.

fn steelhead trout (Salmo

kisutch) and spring chino0k salmon
Zaugg, W. S. and(1984): Changes fn seawatersalmon, Oncorhynchus

amago

Zaugg, W. S. and L. R. McLain

andYamauchi19, 167‑171.

activity related to parr‑smolt transformation

gairdnert): influence 0f photoperiod

andtempe‑

Biochem. Physio1., 45B, 955‑965.

べ二ザケ幼魚、 における海水適応能の 季節変化

伴

頁

俊 ・山

内

略

平

べ二ザケの0 年魚から l 年魚にかけての海水適応能を生理学的に調べるために， l989 年 7 月からl990 年
7 月までの問 ， 月 l 回の海水移行試験を行なった．悔水移行 7 日日まで全個体が生残できたのは，l989 年
8 月および9 月とl990 年 5 月および6 月のみ/‑ った．冬季間の生展率は， 30% 前後まで下がった． また，
海水移行後の魚の血中ナトリウム量が淡水レべル(約 l50mRq/g)

まで ド がったのは，1989 年 8 月および9 月と @990 年 6 月だった．冬季
問は，海水移行
7 日日まで生残した個体でも，血中ナトリウム呈が 200mEq排泄に関与する
鰹のNaを越えた． さらに，血中ナトリウムの

十

， K+‑

ATPaSe爪

は ， @989 年 8 月およびl990

年 6 月に最高値に達した．
， 池中で飼育したべ二ザケの幼魚は， 0 年魚の8 月およびl 年魚の6 月に海水適応能
これらの結果からが高まることがわかった

33