Bulletin of the National Salmon
Resources Center, No. 3: 25 - 28
December 2000

RESEARCH NOTE
Effects of Photoperiod and Water Temperature on Smoltificationof Yearling Sockeye Salmon (Oncorhynchus nerka)
Masatoshi Ban
Reseal-ch Division, National Salmon Resources Center, Fisheries Agency of Japan,
2-2 Nakanoshima, Toyohira-ku, Sapporo 062-0922, Japan(dukehan~salmon.affrc.go.jp)

Abstl-ac,t.- The effects of photoperiod and water temperature on smoltification of yearling sockeye
salmon (0ncorlzync.husnel-ka) were investigated. Yearling sockeye salmon separated into six groups (Ato F) were reared under artificial photoperiod conditions from January to April. The photoperiods ofgroups A and D simulated natural day length. Groups B and E and groups C and F were kept at 13 hand 15 h of daylight, respectively. Throughout the experiment, groups A, B and C were supplied withriver water (3-5'C) and groups D, E and F were supplied with well water (7-8OC). The serum sodium
concentration 24 h after transfer to seawater in groups C and F decreased from 196 mEq/l in January tonearly 160 mEq/l in April. The gill Na',K'-ATPase activity of groups E and F showed a much higher
increase from nearly 3 pmols Pi/mg proteinh in January to 15 and 21 umols Pi/mg proteinh in April.
Fin margin blackening was observed in 6% of fish in group E and 45% of fish in group F in April. These
results indicate that smoltification of yearling sockeye salmon may be affected by increases in photoperiod and higher water temperature accelerates the parr-smolt transformation.

Key words: sockeye salmon, smoltification, photoperiod, water temperature

Introduction
The early life history of anadromous sockeye salmon(Oncorhynchus nerka) is characterized by smoltification preceding seaward migration. Under natural conditions, this phenomenon usually occurs in spring andthus environmental factors such as photoperiod and/or
water temperature may affect the developmental
process of smoltification. For example, underyearling
m a w salmon (0.masou) exposed to longer day lengths
than their natural photoperiod developed their seawater
tolerance unseasonably in autumn (Ikuta et al. 1987).
Juvenile chinook salmon (0. tshawytscha) reared at
17°C reached maximum seawater tolerance two months
earlier than those reared at 9°C (Clarke and Shelbourn1985). Duncan and Bromage (1998) reported that thetiming of the changes from long to short and short tolong day lengths in different photoperiod regimes
induced differences in seasonal profile of the various
parr-smolt changes in Atlantic salmon (Salmo salar). In
Contribution A No. 19 from the National Salmon
Resources Center.
0 2000 National Salmon Resources Center

this study, the effects of photoperiod and water temperature on seawater tolerance of yearling sockeye
salmon were investigated.

Materials and Methods
On January 12, 1 9 9 4 , 6 0 0 yearling sockeye salmon,
which were fertilized at the Chitose Hatchery, National Salmon Resources Center, were separated equally
into six groups (A to F-group) and moved to 100 1tanks.
They were reared under a uniform feeding ration of 3%
body weight per day until April 8, 1994. Throughout theexperiment, groups A, B and C were supplied with riverwater ( 3 5 ° C ) and groups D, E and F were supplied withwell water ( 7 4 % ) . All tanks were shielded with vinyl
cloth and daylight was controlled using two 20 w fluorescent lamps. The photoperiods of groups A and D
were gradually increased from 9.5 h in mid-January to12.5 h in early-April, which simulated the natural photoperiod (Fig. 1). The photoperiods of groups B and E,and groups C and F were fixed at 11 h and 13 h from
mid-January to mid-February, and 13 h and 15 h frommid-February to early-April, respectively. Natural day
length at the beginning of the experiment was 9.5 h in265 I? . 2 %e?%??B-ki 9 -43%
Bull. Natl. Salmon Resources Center, No. 3,2000

mid-January .
During the experimental period, these groups wereused for monthly seawater challenge tests. For eachseawater challenge test, 10 individuals were randomly

ples were drawn from fish in order to measure serum
sodium concentration using an Atomic Absorption
and Flame Emission Spectrometer (Shimadzu, AA640-13). At the same time, the gills for the assay ofcollected from each tank and transferred directly into

Na',K'-ATPase activity were taken from other 10 indi-

artificial seawater at 33 salinity for 24 h. Blood sam-viduals in each freshwater groups. The ATPase activity was measured according to the method of Ban andYamauchi (1991). This was done after measuring fork
lengths and confirming fin margin blackening. Seawater tolerance was assessed by gill Na+,K'-ATPase activity and serum sodium concentration 24 h after the transfer of fish to seawater.
The data were subjected to one-way analysis of variance (ANOVA) followed by Student t-test to determine
significant differences of monthly changes in the gillNa',K'-ATPase activity and serum sodium concentration. A probability level of less than 0.01 was considered significant.

15h5u 13.-0LQ)

P

5011cn9+ Group-C,F I

I-Jan-rn Jan-I Feb-e Feb-rn Feb-l Mar-e Mar-rn Mar-I Apr-e

MonthResults and Discussion

Fig. 1. Experimental designs for changing photoperiod. Groups
A, B and C were kept at 3-5OC and groups D, E and F were kept
at 7-8'C. The photoperiod of groups A and D simulated the natural day length. The e, m and 1 in month show early, middle andlate, respectively.

The mean fork length of fish in each six groups
increased from 106- 1 10 mm in mid-January to 112-131
mm in early-April. All fish transferred to seawater at
each challenge test survived for 24 h. The serum sodium concentration of fish in groups C and F decreased

20018055 160WEY.-c

140

2cg0

120
200

JanFebJanFebMar

Apr5 180G0u)

E20160v)

140

120

MarMonthFig. 2. Changes in serum sodium concentration in groups A-Fof sockeye salmon transferred in seawater for 24 h monthly fromJanuary to April. The groups A, B and C were kept at 3-5OC (upper), and groups D, E and F were kept at 7-8'C (lower).
Bars indicate SE.

JanMarFebAPrMonthFig. 3. Changes in gill Na',K+-ATPase activity in groups A-Fof sockeye salmon reared in fresh water from January to April.
Groups A , B and C were kept at 3-5°C (upper) and groups D, Eand F were kept at 7-8°C (lower). Bars indicate SE.

27

Ban ‑ Smoltification 0f yearling sockeye salmon

from 195.5 and 196.7 mEq/1 ;n mid‑January

to 160.0

seawater adaptability 0f the hatchery reared juvenile

and 157.8mEq/1 tnearly‑Apri1,respectively.
Groups B,sockeye salmon, Oncorhynchus nerka. Sci. Rep.

D and E and group A had serum sodium concentrations
Of 164.9‑168.0 mEq/1 and 180.9 mEq/1, respectively(Fig. 2). These reductions without group A were sig‑
nificant (p<0.01). While seawater‑challenged fish tn all

HOkkaido Salmon Hatchery, 45: 25‑33.
Clarke, W. C., and J. E. Shelboum. 1985. Growth anddevelopment Of seawater adaptability by juvenile fallchino0k salmon (Oncorhynchustshawytscha) ;n rela‑tion to temperature.
Aquaculture, 45: 21‑31.
Duncan, N. J., and N. Bromage. 1998. The effect ofdifferent periods Of constant short days On smoltifi‑
cation in juvenile Atlantic salmon (Salmo salar).
Aquaculture, 168: 369‑386.
Duston, J., and J. D. E. Knox. 1992. Acclimation ofAtlantic salmon (Salmo salar) pan‑ to seawater inautumn:stimulatory effect Of a long photoperiod.

showedareduction fn theserumsodium

con‑centration during the experimental period, fish fn thegroups
C and F showed much lower levels than othergroups. These data suggest that increases Ln photope‑riod are involved in the development ofhyp0‑0smoreg‑

ulatoryabilityfn yearlingsockeye salmon.This result
supports previous findings fn Atlantic salmon (Dustonand Knox 1992; Sigholt et a1. 1998). Furthermore, pre‑sent data suggest that longer daylight had an enhanced
effect On development Of seawater tolerance.
The gill Na@K+‑ATPase activity Of fish tn all groups
increased continuously and showed significant differ‑ences (p<0.01) between mid‑January
and early‑April(Fig. 3). HOwever, groups E and P showed a muchgreater increase tn enzyme
activity from 3.4 and 3.5
umols Pi/mg protein/h ;n mid‑January to 14.9 and 20.9
umols Pi/mg protein/h fn early‑Apri1. The enzyme
activity 0f groups B, C and D and group A were ?.4‑
8.2 umols Pi/mg protein/h and 5.1 @mols Pi/mg pr0‑

tein/hin early‑Apri1,
respectively(Fig.3).Fin margin
blackening was observed fn 6% Of fish fn group E and
45% Of fish fn group F. Fish fn other groups did notshow any change fn fin color. These results show that
increases fn photoperiod together with higher watertemperatureacted to induce development
Of the gill
Na@K@‑ATPase activity and fin margin blackening.
SOlbakken ct a1. (1994) also suggested that elevatedtemperature advanced the development Of gill Na¥IC‑
ATPase activity fn Atlantic salmon. HOwever, deve1‑
opment0f hyp0‑0smoregulatory
ability and elevation
Of the Na@K@ATPase activity were not synchronizedcompletely fn this study. TO investigate the seawater
tolerance Of sockeye salmon, examination Of not only
the gills,but also other osmoregulatory organs such as
the urinary bladder (RichmanIII et a1. 1987) orbranchial mantle (Talbot et a1. 1982) may be necessary.

Aquaculture, 103: 341‑358.
1kuta, K., K. Aida, N. Okumot0, and 1. Hanyu. 1987.
Effects 0f sex steroids 0n the smoltification Of masu
salmon, Oncorhynchus
masou.
Gen. COmp. End0‑

crino1.,65:99‑110.
Richman II1, N. H., S. Taidediaz, R. S. Nishioka, P.
Prunet, and H. A. Bern. 1987. Osmoregulatory
andendocrine relationships with chloride cell morpho1‑
0gy and density during smoltification fn coho salmon(Oncorhynchus kisutch).
Aquaculture, 60: 265‑285.
Sigholt, T., T. Asgard, and M. Staumes. 1998. Timing
Of parr‑smolt transformation ;n Atlantic salmon(Salmo salar): effects Of changes ;n temperature andphotoperiod. Aquaculture, 160: 129‑144.
SOlbakken, V. A., T. Hansen, and S. 0. Stefansson.
1994. Effects Of photoperiod and temperature
ongrowth and parr‑smolt transformation tn Atlanticsalmon (Salmo salar L.) and subsequent perfor‑mance
fn seawater. Aquaculture, 121: 13‑27.
Talbot, C., F. B. Eddy, and J. JOhnston. 1982.
Osmoregulation・groupsin salmon

andsea

口長と水温がべ 二ザケ ] 年 魚の スモ ルト化に与える影響
伴 真俊

Acknowledgements
wish to express our appreciation to the staff ofthe Chitose Branch, National Salmon Resources Cen‑ter for theireffortsupplying the experimental fish.
Thanks also to Dr. JillB. K. Leonard for revision Or thisWemanuscript.

べ二ザケ l年魚を 100 個体ずっ 6 群 (A‑F 群) に分け， l月から 4 月まで人工的にコントロ―

ル した異なる日展と水温条件で 飼育した． 日艮は ，A 群と D 群を日外口長と同じに設定し ，B，c 群を 3‑5 。C ，D，E，F 群を ?‑8 。C に設定した．実験終了時の 4 月に， スモルトの特長であ るつ
まBan, M., and K. Yamauchi. 1991. Seasonal changes tn

B 群と E 群を 3 時間明朝 口 時間 暗期 ， C 群と F 群を 15 時間明朗 9時間 暗期に設定した．水温は， A ，References

trout alevins

Exp.BioL, 101:61‑70.

黒 を発現し ，最も顕者な 鯉の Na" ， K"‑ATPase

上昇を示したのは E 群と F 群 だった ．

活性のまた，海水移刊

28

さけ・ます安源管理センター研報 Bul1. Nat1.SalmonResourcesCenter,No

24 時間後の血中ナトリウム 濃度は， C 群と F 群が最も低い値を示した． この結果から ，口長の増加が スモ

ルト化の引き 金となること ，水温が高いほどスモ ルト化が加速されることが 示唆された ．

． 3， 2000