さ け・ま す 資 源 管 理 セ ン タ ー
研究報告 第 4 号 13-18 頁
2001 年 12 月

Bulletin of the National Salmon
Resources Center, No. 4: 13-18
December 2001

RESEARCH NOTE
Variation in Lipid Content in the Muscle of Chum and Pink
Salmon in the Gulf of Alaska in May 1999
Tetsuichi Nomura*1, Katherine W. Myers*2, Christine M. Kondzela*3,
James M. Murphy*3 , Hiromi Honma*1, and H. Richard Carlson*3*1

Research Division, National Salmon Resources Center,
2-2 Nakanoshima, Toyohita-ku, Sapporo 062-0922, Japan.
(nomurat@salmon.affrc.go.jp)*2
School of Aquatic and Fishery Sciences, University of Washington,
Box 355020, Seattle, WA 98195-5020, USA*3
Auke Bay Laboratory, Alaska Fisheries Science Center, National Marine Fisheries Service,11305 Glacier Highway, Juneau, Alaska 9980-8626, USA

Abstract. − We report on a study of the total lipid content (TL) of chum and pink salmon in the
Gulf of Alaska in May 1999. Chum and pink salmon were caught by surface trawl net in the Gulf of
Alaska during a spring cruise of the F/V Great Pacific. TL was extracted from the muscle of 99
chum and 50 pink salmon by Folch's method using chloroform/methanol and measured
gravimetrically. A significant difference in the total lipid content by ocean age was observed inchum salmon. Younger chum salmon (ocean age-.1 and .2) had lower lipid content than older fish(ocean age-.3 and .4). Mean TL in pink salmon was 2.6% in females and 2.7% in males. Our results
suggest that low lipid content, previously observed in hig-seas salmon during the winter season, is
prolonged into the spring in young chum and pink salmon.
Key words: total lipid content, muscle, chum salmon, pink salmon, spring, Gulf of Alaska

Introduction
The quantity of lipid has been used as a biochemical index of trophic condition in a variety ofcontexts for both freshwater and marine fish (Novotony and Beeman 1990). Dietary lipids play an important role in providing energy in carnivorous fish
like salmonids due to their limited ability to utilize
carbohydrates as an energy source (Watanabe 1982).
Although there have been a large number oflipid studies on cultured fish and artificial food (Wilson 1991), little is known about high-seas salmonid
lipid content. Azuma et al. (1998) reported on thegrowth characteristics of Pacific salmon through examination of triglycerol and protein content, and nucleic acid ratios. In our previous paper, lipid content
Contribution A No. 24 from the National Salmon
Resources Center.
賛 2001 National Salmon Resources Centerand fatty acids were examined to investigate trophic
condition of chum (Oncorhynchus keta) and pinksalmon (O. gorbuscha) in the North Pacific Oceanin winter (Nomura et al. 2000). A low lipid content
in the muscle and a high percentage of docosahexaenoic acid in fatty acid composition of neutral lipid
were observed in chum and pink salmon in winter.
Information on the lipid content of salmonids
during high-seas migrations is useful to estimate
their trophic condition, growth, and survival. In general, it is supposed that salmonids resume feeding in
spring, and lipid content level in the muscle of thesefish may be higher than in winter. But there is noprevious report of lipid content in high-seas salmonids in spring. In this report, we studied lipid content in the white muscle of chum and pink salmoncaught in the Gulf of Alaska in the spring of 1999.

Materials and Methods
Chum and pink salmon were caught by surfaceさけ・ます資源管理センター研報 Bull. Natl. Salmon Resources Center, No. 4, 2001

14

Table 1. Sampling station, date, location, number of fish sampled by ocean age, and seawater temperature (ST) in the Gulf of
Alaska in the spring of 1999.

Station

Date

Longitude

Latitude

(W)

(N)

Chum

Pink

Ocean age

Ocean age

1

2

3

4

5

1

ST*
(oC)

May 4

166o38'54o06'

0

0

0

1

0

0

3.1-3.2

May 5

166 43'o

53 26'

0

0

0

3

0

0

3.2-3.4May 5

o

166 23'o

53 09'

0

0

0

1

0

0

3.3

4

May 5

o

166 07'o

52 51'

0

0

0

2

1

0

4.0-4.1

5

May 6

165o00'50o58'

0

0

1

4

1

0

3.3

May 6

165 00'o

49 59'

0

0

0

2

1

0

3.4-3.5May 6

o

164 59'o

49 02'

0

0

1

5

1

0

3.9

8

May 7

o

165 00'o

47 59'

0

0

0

3

0

1

4.7-4.89

May 7

165o00'47o00'

0

0

0

1

0

4

4.9

May 7

o

165 01'o

46 54'

0

0

2

2

1

4

5.0

11

May 7

o

165 00'o

46 23'

0

0

0

0

0

12

5.1-5.5

12May 8

164o59'45o00'

0

0

1

1

0

4

6.5-6.6May 8

o

164 59'o

43 58'

3

7

2

1

0

0

6.5-6.7

May 16o

144 59'o

42 34'

0

0

0

0

0

7

8.1-8.2

15

May 16o

144 58'o

43 00'

10

2

0

0

0

2

8.2-8.3

16

May 16145o00'43o51'

0

2

0

0

0

2

7.8-7.9

May 17o

145 00'o

45 01'

3

3

0

0

0

12

7.1-7.2

May 17o

145 00'o

46 00'

0

0

0

0

0

2

6.7

19

May 19o

145 00'o

50 57'

0

0

1

1

0

0

5.1-5.3

20

May 19145o00'52o54'

0

0

3

0

0

0

4.6-4.9

May 20o

144 58'o

54 31'

0

0

2

0

0

0

4.8-4.9

May 20o

144 59'o

55 00'

0

1

11

2

0

0

4.7-4.8

23

May 20o

144 59'o

55 31'

0

0

2

0

0

0

5.0-5.2

24

May 21144o59'56o00'

0

0

7

1

0

0

5.3-5.7

16

15

33

30

5

50

1
2
3

6
7

10

13
14

17
18

21
22

o

o

Total
*ST, Seawater temperature at head rope of trawl net.

trawl net in the Gulf of Alaska during a spring
cruise of the F/V Great Pacific (Table 1) (Carlson etal. 1999). Salmon ages were determined by examination of scale patterns. Ocean age was designated by
the European method, whereby a dot followed by anumber indicates the number of winters in theocean, for example, an age-.1 salmon spent one winter in the ocean. The fork lengths (FL in cm) andweights (BW in g) of the salmon were measured andused to calculate the condition factor (((BW)/(FL)3)
× 1,000). The white muscle was sampled from thedorsal muscle directly behind the head, and muscle
samples were frozen at -30oC until analyzed.
Total lipids (TL) in the white muscle were ex-

tracted with chloroform/methanol by the method of
Folch et al. (1957) and measured gravimetrically.
Lipids were extracted by homogenizing the whitemuscle (10 g) with 50 ml of methanol and 120 ml ofchloroform. The homogenate was filtered through alipid free paper into glass vessel. The crude extract
and water were mixed in a separatory funnel in the
proportions 8:4:3 by volume. The lower phase wascollected, and solvent was evaporated with rotary
evaporator.
The resulting values were tested for significant
differences using analysis of variance (ANOVA) followed by Turkey' multiple comparisons test
(p<0.05).

Nomura et al. − Lipids in spring chum and pink salmon

15

Table 2. Biological parameter and total lipid content of chum and pink salmon caught in the Gulf of Alaska in May 1999 byocean age.
No. ofFork length

Body weight

Condition

fish

(cm)

(g)

factor730.0 (1.63) *1

340 (60)

12.31 (0.58)

1.4 (0.47)

0.9-2.3 *2

Male

9

30.4 (2.12)

320 ( 51)

11.43 (0.96)

1.2 (0.96)

0.9-1.4

Female1038.9 (1.59)

640 ( 110)10.80 (0.80)

1.9 (0.91)

1.0-4.1

Male

5

39.6 (1.69)

650 ( 54)

10.41 (0.56)

1.6 (0.35)

1.3-2.2

Female2254.9 (4.53)

2,062 (505)

12.15 (1.06)

4.0 (2.08)

1.2-10.9

Male11

58.8 (3.34)

2,452 (490)11.90 (1.29)

3.9 (2.10)

0.9-7.4

Female1657.5 (2.18)

2,290 (271)

11.97 (1.10)

4.9 (3.33)

1.4-15.6

Male

14

60.0 (3.53)

2,605 (727)

11.75 (1.42)

3.1 (1.80)

1.0-6.4

Female358.2 (3.71)

2,120 (380)10.68 (0.67)

3.6 (0.76)

2.7-4.2

Male2

61.6 (4.95)

2,950 (1,060)

12.31 (1.55)

5.1 (5.57)

1.1-9.0

Female1535.9 (3.04)

480 (110)10.22 (0.94)

2.6 (1.29)

0.8-6.5

Male

35

36.5 (3.33)

509 (128)10.36 (1.03)

2.7 (1.34)

1.1-6.2

Species

Ocean age

Sex

Chum

1

Female

2

3

4

5

Pink

1

Total lipid content (%)

1* mean (SD)* 2 range

Results
Chum salmon
TL in female and male age-.1 fish was low andincreased with increasing ocean age (Table 2, Fig. 1).
There was a significant difference in TL between
ocean age-.1 and .4 female chum salmon. In female
chum salmon, a significant difference in TL wasalso observed between ocean age-.2 and .4 fish. TL
in ocean age-.1 male chum salmon was significantly
lower than in ocean age-.3 male fish.
A positive relationship between body weight andTL was observed in ocean age-.4 male fish (Fig. 2).
There was no significant relationship between bodyweight and TL in other ages and sexes of fish. A
positive relationship between condition factor andTL was observed in ocean age-.2 female, age-.3
male, and age-.4 male fish. There was no significant
relationship between condition factor and TL inother ages and sexes fish.
Pink salmon
All pink salmon in the samples were ocean age.1. TL was 2.6% in female and 2.7% in male (Table2). There was no significant difference in the average of TL between female and male pink salmon(p>0.05). There was a negative correlation(R2 =0.176) between body weight and TL in the maleFig. 1. Total lipid content in the white muscle in chumsa lmon caught in the Gulf of Alaska in May 1999 by oceanage. Sample sizes are shown in Table 2. Bars are means, andlines are SD. Letters at the top of each bar summarize the result of Turkey's multiple comparison (ANOVA). Data points
sharing the same letter are not significantly different(p>0.05).

fish, and a positive correlation (R2=0.162) between
condition factor and TL in male pink salmon (Fig.
3).

さけ・ます資源管理センター研報 Bull. Natl. Salmon Resources Center, No. 4, 2001

16

Fig. 3. Relationship between total lipid content in the whitemuscle of pink salmon and body weight (upper) or condition
factor (lower). Open and close circles indicate female (n=15)
and male (n= 35) fish, respectively. The regression lines weredrawn with a solid line for female a nd broken line for male.

Fig. 2. Relationships between total lipid content in the whitemuscle of chum salmon and body weight (left) or condition
factor (right) by ocean age . Open and close circles indicate female (n=58) and male (n=41) fish, respectively. The regression lines were drawn with a solid line for female and broken
line for male.

Discussion
In this study, we found a significant differenceby ocean age in total lipid content in the white muscle of chum salmon caught in the Gulf of Alaska inspring. We conclude that the effect of age must be
taken into consideration when examining lipid levels in salmon in offshore waters. The average TL
content in winter was 1.1% in chum salmon and1.7% in pink salmon (Nomura et al. 2000). Present
results for TL content of ocean age-.1 and .2 chumsalmon, and pink salmon in spring were similar to
those in winter, indicating that lipid levels had notincreased in early spring. Younger chum and pinksalmon still had lower lipid levels than older salmon
in spring, and the starved condition observed by Nomura et al. (2000) in winter seemed to be continued
even in spring in the Gulf of Alaska.
Ocean environmental conditions, especially water temperatures, play an important role in the regulation of metabolism in marine fish. Bioenergetic
models show that high-seas salmon expend more energy for metabolism at high temperatures than at
low temperatures (Davis et al. 1998; Walker et al.
2000). Sea surface temperature (SST) was lower
than 4 oC at many stations where chum salmon werecaught in our study, but the ocean age-.1 and .2 fish
were primarily caught at SSTs between 6.5-8.3o C(Table 1). The surface water layers along the survey
transects were well-mixed to a depth of a least 100
m (Carlson et al. 1999), so that young salmon would
have had to migrate substantial horizontal or verticaldistances to find cooler water temperatures. Morestudies are needed to reveal effects of annual andseasonal variation in ocean conditions on lipid content in young chum and pink salmon.
Our results cannot explain the reason for the observed low lipid content of young chum salmon inNomura et al. − Lipids in spring chum and pink salmon

spring 1999. At the time of capture, most young
chum salmon appeared to be actively feeding on awide variety of zooplankton prey, and percentagesof fish with empty stomachs were lower and stomach contents weight as a percentage of body weight
were higher than in chum salmon samples collectedfrom the same region in July 1999 (Carlson et al.
1999; Myers et al. 2000). During their ocean migrations salmon use much energy for movement andcontrol of metabolism. Lipid is an important energy
source for fish, and thus low lipid content in young
chum salmon indicates that there was not enough intake of dietary lipid, or that they expended much
lipid on growth. A negative correlation between triacylglycerol content and RNA:DNA ratio demonstrates that juvenile chum salmon slow down their
growth rate to maintain their energy reserve (Azuma
et al. 1998). Low lipid content in young chum andpink salmon in spring may have a significant effecton their ocean growth and survival.
There are many papers discussing the association of lipid levels with maturation (Kiessling et al.
1991; Thorpe et al. 1991; Kadri et al. 1996; Shearer
and Swanson 2000). We did not evaluate the relationship between maturation and lipid levels inchum salmon, because we judged maturation only
by visual examination of gonads. Pooled-years
analyses of historical high- seas salmon data (19561971) have shown that older, maturing chum salmon
tend to be distributed farther to the north than
younger, immature chum salmon in the spring North
Pacific Ocean (Neave et al. 1976). We observed little overlap in the distribution of immature and maturing chum salmon during our May 1999 survey,
and maturing chum salmon, caught in northern areas
along the transect, had higher stomach content
weights as a percentage of body weight than immature chum salmon, caught in southern areas (Carlson
et al. 1999). The lack of overlap in spring high seas
distribution of immature and maturing chum salmon
may serve to maximize the growth potential of maturing fish and minimize intra specific competitive
feeding interactions, perhaps at the expense of reduced growth rates of younger age groups. Further
investigation of seasonal changes and annual variation in lipid content of each age and maturity groupof chum salmon will be important for understanding
their ocean survival, growth, and fecundity.

17

Acknowledgements
The authors thank the U.S. National Marine Fisheries Service, Alaska Fisheries Science Center,
Auke Bay Laboratory, Juneau for inviting the seniorauthor (T. N.) to participate in the F/V Great Pacificcruise in the spring of 1999. We would like to express our appreciation to the captain, Charles Bronson, and his crew on board the F/V Great Pacific for
their help in collecting samples during our researchcruise.

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1999 年 5 月にアラスカ湾で採集されたサケとカラフ
トマスの筋肉脂質含量
野村哲一・K. W. Myers・C. M. Kondzela・J. M. Murphy
本間裕美・H. R. Carlson
1999 年 5 月にアラスカ湾でトロール網で採集されたサケ 99 尾とカラフトマス 50 尾の筋肉脂質含量について検討した．サケでは海洋年齢 1 年および 2 年
魚の筋肉脂質含量は 3 年魚および 4 年魚より有意に低い値を示した．カラフトマスでもサケと同様の低い脂質含量であった．海洋年齢 1 年および 2 年魚の平均脂質含量は，越冬期のサケやカラフトマスの含量とほぼ同様の値であり，越冬期に観察された飢餓状態が若齢魚では春季にも継続していることが示唆された．海洋生活期のサケやカラフトマスの脂質含量を検討する際は年齢の影響を十分考慮する必要がある．