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Physiological changes in skeletal muscle by maturation-spawning of non-migrating female atlantic salmon, Salmo salar
Comp. Biochem. PhysioLVol. 101B,No. 3, pp. 299-301, 1992 Printed in Great Britain
0305-0491/92$5.00+ 0.00 © 1992PergamonPress plc
PHYSIOLOGICAL CHANGES IN SKELETAL MUSCLE BY MATURATION-SPAWNING OF NON-MIGRATING FEMALE ATLANTIC SALMON, SALMO SALAR A. VON DER DECKEN The Wenner-Gren Institute for Experimental Biology, University of Stockholm, S-106 91 Stockholm, Sweden (Tel: 46 8164131; Fax: 46 8152396) (Received 9 September 1991) Abstract--l. Physiological properties of epaxial muscle of non-migrating female Atlantic salmon (Salmo salar) were compared between non-spawning and spawning fish. 2. The rise in blood plasma vitellogenin, and liver and gonadal weights confirmed the maturationspawning condition. 3. In the spawning females DNA, glycogen and acid proteinase activity were elevated per g wet weight of muscle, while protein and RNA content of the sarcoplasmic fraction and RNA of the myofibrillar fraction were diminished. 4. The data suggest that characteristic changes occur in skeletal muscle by the process of maturation and spawning, which are independent of the physical load of upstream migration.
food components was, fat 19.6%, protein 49.1%, carbohydrate 10.5%, vegetable fiber 1.9%, ash 9.5%, water 9.4%. Digestible energy was 15 MJ/kg food. The fish were fed to satiety twice daily. In October 1990 roe was taken from the spawning fish. All fish were killed 2 weeks later. The blood was collected. The tissues were weighed and immediately frozen on dry ice and then kept at -80°C until analysis.
INTRODUCTION In Atlantic salmon (Salmo salar) maturation of the gonads is closely followed by upstream migration and spawning. A large a m o u n t of energy is required to support the biochemical and physical activities during the period of reproduction (for details see Love, 1970). Depletion of carbohydrates in liver and lipids in muscle indicates that these macromolecules are the predominant energy source (Love, 1970; Ng and Idler, 1983). The free amino acid pool in muscle and blood shows little change according to the stage of maturation (Cowey et al., 1962). During spawning migration the protein content in muscle decreases (Mommsen et al., 1980; A n d o et al., 1986). Maturation of the gonads may be the initial cause of the decrease observed, while later on, during the migratory journey, physical activity will accelerate the degradation of the muscle proteins. Rearing Atlantic salmon in net cages in seawater offers the opportunity for studying separately the effects of maturation and spawning on muscle composition without the additional load on body metabolism of migratory activity. The present study was undertaken to assess properties of the epaxial muscle in female Atlantic salmon. Non-migrating spawning fish were compared with female salmon who had failed to undergo gonadal maturation. MATERIALS AND METHODS
Animal treatment and sample handling Female Atlantic salmon (Salmo salar) in the 6th year were of the Lule-~ilven stock. The fish had been reared for 2 years in net cages of 200 m 3 in the Baltic Sea (63°30'N, 20°E, salinity 0.2-0.4%) with 20-30 fish in each cage. They were exposed to the ambient temperature and photoperiod. The fish were fed the Laktamin Ix) (Laktamin AB, Stockholm) standard salmon food. The percentage distribution of the
Sarcoplasmic and myofibrillar fraction of skeletal muscle The tissue was homogenized and separated into a sarcoplasmic and myofibrillar fraction (Nazar et al., 1991) but using a centrifugation time of 20 instead of 15 rain. Immunological assay The total homogenate of muscle was analyzed for myosin heavy chain by the ELISA technique using antibodies specific for that protein (Persson et aL, 1991). Vitellogenin was analyzed in blood plasma by the same technique using antibodies specific for vitellogenin from Atlantic salmon (Olin and yon der Decken, 1989; Olin et aL, 1989). Analyses Proteins were determined by the Coomassie Brilliant Blue method (Bradford, 1976) using bovine serum albumin as a standard. DNA was analyzed by the fluorometric method using salmon DNA as a standard (Setaro and Morley, 1976). RNA was analyzed by precipitating the cellular fractions in 0.4 M HCIO4, followed by extraction of the precipitate in 0.4M HC104 for 18rain at 70°C. The absorbance of the extract was measured at 260 nm and RNA calculated on the basis of 34.2 absorbance units/mg of RNA. Glycogen was analyzed (Harris et aL, 1974) and expressed as mg glucose obtained after enzymic degradation of glycogen. Acid proteinase activity in skeletal muscle was determined in the supernatant obtained after centrifugation for 30 min at 15,000g of the muscle homogenate (Momm~n et aL, 1980). Hemoglobin was used as substrate and the tyrosine released was determined by a fluorescent method (Ambrose, 1974). The results are expressed as nag tyrosine released from hemoglobin/hr.
299
300
A. VON DER DECKEN
Table I. Body weight, liver and gonadal wet weight as % of body weight and blood plasma proteins in non-spawning and spawning salmon Per ml of plasma Fish Body weight HSI* GSl? Protein (mg) Vitellogenin (rag) Non-spawning (14) Spawning (21)
2875 5: 240" 2660 5: 200"
1.16 _+0.04* 1.26 5:0.03 b
0.51 5:0.05 s 1.13 5:0.06 b
43.02 _+2.12' 53.11 5:3.45 b
< 10- 3, 9.57 5:1.69 b
*Liver wet weight as % of body weight; ?gonadal wet weight as % of body weight. The results are the means 5: SEM. The numbers of fish are given in parentheses. Means with different superscript letters within a column are significantly different, P < 0.05. Table 2. Content of protein, DNA, and sarcoplasmic and myofibrillar protein and RNA in the muscle of non-spawning and spawning salmon Per g wet weight of muscle RNA (rag)
Protein (mg) Fish Non-spawning Spawning
Total
Sarcoplasmic
MyofibriUar
Sarcoplasmic
Myofibrillar
DNA (rag)
129.3 + 3.3' 116.8 + 3.6b
60.2 + 1.7' 53.4 + 2.5b
65.1 + 2.0' 65.0 + 2.0'
0.369 + 0.012' 0.285 + 0.009 b
0.388 + 0.012" 0.336 + 0.009b
0.747 + 0.025' 0.661 + 0.025 b
The results are the means + SEM of 10 fish per group. Means with different superscript letters within a column are significantly different, P < 0.05.
Statistical evaluation
DISCUSSION
The results are expressed as means + SEM. Data were analyzed using one-way analysis of variance followed by Student's t-test (Snedecor and Cochran, 1980).
RESULTS
Table 1 shows that the weights of liver and gonads per 100 g body weight (hepato- and gonadosomatic indices) were significantly higher in the spawning group compared with the non-spawning fish of similar age and body weight. The maturation process was noticeable also as a mg level of vitellogenin in the plasma and an elevated plasma protein content (Table 1). Total protein content per g wet weight of muscle decreased in the spawning group (Table 2). The decrease was confined to the sarcoplasmic and not the myofibrillar proteins. With the decrease in total protein and the unchanged myofibrillar protein content the protein myosin heavy chain was expected to rise per mg of total protein. Myosin heavy chain/mg of total protein was 0.225+0.010 and 0.240 + 0.009 for the non-spawning and the spawning group, respectively. The differences between the groups were not significant. RNA content was diminished by 23% in the sarcoplasmic and 13% in the myofibrillar fraction of the spawning group, and the level of DNA per g wet weight increased significantly (Table 2). The event of spawning evoked a 1.7-fold increase in acid proteinase activity, and a significantly increased accumulation of glycogen by 25% (Table 3). Table 3. Glycogen content and acid proteinase activity in the muscle of non-spawning and spawning salmon Fish Non-spawning Spawning
Per g wet weight of muscle Acid proteinase activity* Glycogen? 0.254 5:0.008 s 0.442 + 0.016b
6.49 5: 0.27' 8.17 5:0.21 b
*Acid proteinase activity is given as mg tyrosine released from the added substrate hemoglobin per hour. ?Glycogen is expressed as mg glucose. The results are the means + SEM of 10 fish per group. Means with different superscript letters within a column are significantly different, P < 0.01.
The major differences in epaxial muscle constituents between non-spawning and spawning females in the absence of migration were focused on the proteins and RNA of the sarcoplasmic fraction, protein degradation, glycogen and DNA content, as well as the expected rise in plasma vitellogenin and protein levels. The elevated DNA content per g wet weight of muscle in the spawning group suggested a diminished amount of other constituents. During the shift from sea to fresh water the moisture content of muscle decreases by 4% (Cowey et al., 1962). This would not be sufficient to account for the 13% increase in DNA in the spawning females. The rise in DNA could partially be attributed to the decline in sarcoplasmic proteins. The lipid content of muscle decreases drastically during spawning migration (Love, 1970; Ando et al., 1985; Sargent et al., 1989). It has been reported that an inverse relationship exists between the lipid and water content of the fish whereby catabolized lipid is replaced by an equal volume of water (Sargent et al., 1989). If the water is retained in muscle its moisture content will increase, and the loss of lipids cannot be made responsible for the apparent rise in DNA observed here. In Oncorhynchus nerka not all the lipids in muscle are used for energy purpose (Idler and Bitners, 1960). Part of the lipids are transferred from muscle to the gonads and therefore are not replaced in muscle by catabolic water from the lipids. In the Argentine hake (Merluccius hubbsi) energy content in muscle decreases during the period of gonadal growth confirming an energy transfer from one tissue to another (Montecchia et aL, 1990). The elevated level of muscle glycogen indicated that the carbohydrate was not utilized as a major energy source during the maturation-spawning season. The rise in glycogen pointed towards an increased uptake of glucose, as gluconeogenic enzyme activities in fish muscle appear to be low (for review see Suarez and Mommsen, 1987). It has been reported that acid proteinase activity increases during spawning migration of salmon (Mommsen et ai., 1980; Ando et ai., 1986). A close relationship between proteinase activity and the hormone condition of fishes has been demonstrated (Ando et al., 1986). When immature salmon is treated with 17-~ estradiol acid proteinase activity is elevated
Spawning and non-spawning female salmon (Olin et al., 1991). In the present work acid proteinase ' activity increased in the spawning group and might have led to the diminished content of the sarcoplasmic proteins. These results support the notion that protein degradation in muscle is related to the process of maturation and spawning. However, the physical activity of upstream migration will add to the event of protein degradation (Ando et aL, 1986). The sarcoplasmic reticulum controls the relaxation-contraction mechanism of muscle by controlling Ca 2+ levels in the sarcoplasm. R N A content is an indirect measure of the capacity for protein synthesis. The decrease in concentration observed in the sarcoplasmic fraction suggested a fall in protein synthesis activity leading to the conclusion that the sarcoplasmic protein content was affected by a low synthesis as well as an elevated degradation (Ando et al., 1986). The diminished R N A content of the myofibrillar fraction suggested a decrease in protein synthesis activity. The moderate but significant changes observed in muscle were insufficient to explain the inability of the non-spawning females to trigger the events of vitellogenesis. Maturation and spawning did not influence the physiological functions of muscle to such an extent as would lead to the often-occurring death observed after spawning. The additional load of upstream migration of the fish is required to evoke pronounced changes in muscle and impair the metabolic processes of the body. In conclusion, in the absence of upstream migration, maturation and spawning together led to changes in muscle constituents which were controlled by the metabolic processes of reproduction. In contrast to the myofibrillar cell compartments, the sarcoplasmic constituents responded readily to the metabolic demands of maturation and spawning. Bearing in mind the upstream migration that occurs under natural conditions in the wild, the myofibrillar proteins must be saved to later support the physical exertion during the migratory journey. Acknowledgements--The work was supported by the Swedish Council for Forestry and Agriculture, Project No. 0851/89 V 82:3. The Center for Environmental Research in UmeA, Sweden, supported the farming and feeding of the fish. The competent technical assistance of Ms Solveig Sundberg is gratefully acknowledged.
REFERENCES
Ambrose J. A. (1974) Fluorometric measurement of tyrosine in serum and plasma. Clin. Chem. 20, 505-510. Ando S., Hatano M. and Zama K. (1985) Deterioration of chum salmon (Oncorhynchus keta) muscle during spawning migration. I. Changes in proximate composition of chum salmon muscle during spawning migration. Comp. Biochem. Physiol. 80B, 303-307. Ando S., Hatano M. and Zama K. (1986) Protein degradation and protease activity of chum salmon
301
(Oncorhynchus keta) muscle during spawning migration. Fish Physiol. Biochem. 1, 17-26. Bradford M. M. (1976) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Analyt. Biochem. 72, 248-254. Cowey C. B., Daisley K. W. and Parry G. (1962) Study of amino acids, free or as components of protein, and of some B vitamins in the tissues of the Atlantic salmon, Salmo salar, during spawning migration. Comp. Biochem. Physiol. 7, 29-38. Harris R. C., Hultman C. and Nordesj6 L.-O. (1974) Glycogen, glycolytic intermediates and high-energy phosphates determined by biopsy samples of musculus Quadriceps femoris of man at rest. Methods and variance of values. Scand. J. clin. Invest. 33, 109-120. Idler D. R. and Bitners I. (1960) Biochemical studies on sockeye salmon during spawning migration. IX. Fat, protein and water in the major internal organs and cholesterol in the liver and gonads of the standard fish. J. Fish. Res. Bd Can. 17, 113-122. Love R. M. (1970) The Chemical Biology of Fishes, Vol. 1, pp. 97-125. Academic Press, London. Mommsen T. P., French C. J. and Hochachka P. W. (1980) Sites and patterns of protein and amino acid utilization during the spawning migration of salmon. Can. J. Zool. 58, 1785-1799. Montecchia C. L., Crupkin M. and Trncco R. E. (1990) Seasonal variations in biochemical and physicochemical properties of actomyosin and energy content of the liver, gonads and muscle of mature Argentine hake, Mercuccius hubbsi Marini. J. Fish Biol. 37, 837-843. Nazar D. S., Persson G., Olin T., Waters S. and yon der Decken A. (1991) Sarcoplasmic and myofibriUar proteins in white trunk muscle of salmon (Salmo salar) after estradiol treatment. Comp. Biochem. Physiol. 98B, 109-114. Ng T. B. and Idler D. R. (1983) Yolk formation and differentiation in teleost fishes. In Fish Physiology (Edited by Hoar W. S., Randall D. J. and Donaldson E. M.), Part A, Vol. 9, pp. 373-404. Academic Press, New York. Olin T. and yon der Decken A. (1989) Yolk proteins in salmon (Salmo salar) oocytes, eyed eggs, and alevins differing in viability. Can. J. Zool. 68, 895-900. Olin T., Westman A. and yon der Decken A. (1989) Time and temperature dependent appearance of vitellogenin in Golgi vesicles and serum after estrogen treatment of salmon (Salmo salar). J. exp. Zool. 249, 213-220. Olin T., Nazar D. S. and yon der Decken A. (1991) Response of epaxial muscle and liver to 17-~ estradiol in fed and starved Atlantic salmon (Salmo salar). Aquaculture 99, 179-191. Persson G., L6fberg E. H. A. and yon der Decken A. (1991) Antigenicity of myosin heavy chain from skeletal muscle of fish species and humans as determined by the ELISA technique. Biochem. Arch. 7, 1-11. Sargent J., Henderson R. J. and Tocher D. R. (1989) The Lipids. In Fish Nutrition (Edited by J. E. Halver), pp. 153-217. Academic Press, San Diego, CA. Setaro F. and Morley C. G. D. (1976) A modified fluorometric method for the determination of microgram quantities of DNA from cell or tissue cultures. Analyt. Biochem. 71, 313-317. Snedecor G. W. and Cochran W. G. (1980) Statistical Methods, 7th Edn, pp. 54-56. The Iowa State University Press, Ames, IA. Suarez R. K. and Mommsen T. P. (1987) Gluconeogenesis in teleost fishes. Can. J. Zool. ~ , 1869-1882.
0305-0491/92$5.00+ 0.00 © 1992PergamonPress plc
PHYSIOLOGICAL CHANGES IN SKELETAL MUSCLE BY MATURATION-SPAWNING OF NON-MIGRATING FEMALE ATLANTIC SALMON, SALMO SALAR A. VON DER DECKEN The Wenner-Gren Institute for Experimental Biology, University of Stockholm, S-106 91 Stockholm, Sweden (Tel: 46 8164131; Fax: 46 8152396) (Received 9 September 1991) Abstract--l. Physiological properties of epaxial muscle of non-migrating female Atlantic salmon (Salmo salar) were compared between non-spawning and spawning fish. 2. The rise in blood plasma vitellogenin, and liver and gonadal weights confirmed the maturationspawning condition. 3. In the spawning females DNA, glycogen and acid proteinase activity were elevated per g wet weight of muscle, while protein and RNA content of the sarcoplasmic fraction and RNA of the myofibrillar fraction were diminished. 4. The data suggest that characteristic changes occur in skeletal muscle by the process of maturation and spawning, which are independent of the physical load of upstream migration.
food components was, fat 19.6%, protein 49.1%, carbohydrate 10.5%, vegetable fiber 1.9%, ash 9.5%, water 9.4%. Digestible energy was 15 MJ/kg food. The fish were fed to satiety twice daily. In October 1990 roe was taken from the spawning fish. All fish were killed 2 weeks later. The blood was collected. The tissues were weighed and immediately frozen on dry ice and then kept at -80°C until analysis.
INTRODUCTION In Atlantic salmon (Salmo salar) maturation of the gonads is closely followed by upstream migration and spawning. A large a m o u n t of energy is required to support the biochemical and physical activities during the period of reproduction (for details see Love, 1970). Depletion of carbohydrates in liver and lipids in muscle indicates that these macromolecules are the predominant energy source (Love, 1970; Ng and Idler, 1983). The free amino acid pool in muscle and blood shows little change according to the stage of maturation (Cowey et al., 1962). During spawning migration the protein content in muscle decreases (Mommsen et al., 1980; A n d o et al., 1986). Maturation of the gonads may be the initial cause of the decrease observed, while later on, during the migratory journey, physical activity will accelerate the degradation of the muscle proteins. Rearing Atlantic salmon in net cages in seawater offers the opportunity for studying separately the effects of maturation and spawning on muscle composition without the additional load on body metabolism of migratory activity. The present study was undertaken to assess properties of the epaxial muscle in female Atlantic salmon. Non-migrating spawning fish were compared with female salmon who had failed to undergo gonadal maturation. MATERIALS AND METHODS
Animal treatment and sample handling Female Atlantic salmon (Salmo salar) in the 6th year were of the Lule-~ilven stock. The fish had been reared for 2 years in net cages of 200 m 3 in the Baltic Sea (63°30'N, 20°E, salinity 0.2-0.4%) with 20-30 fish in each cage. They were exposed to the ambient temperature and photoperiod. The fish were fed the Laktamin Ix) (Laktamin AB, Stockholm) standard salmon food. The percentage distribution of the
Sarcoplasmic and myofibrillar fraction of skeletal muscle The tissue was homogenized and separated into a sarcoplasmic and myofibrillar fraction (Nazar et al., 1991) but using a centrifugation time of 20 instead of 15 rain. Immunological assay The total homogenate of muscle was analyzed for myosin heavy chain by the ELISA technique using antibodies specific for that protein (Persson et aL, 1991). Vitellogenin was analyzed in blood plasma by the same technique using antibodies specific for vitellogenin from Atlantic salmon (Olin and yon der Decken, 1989; Olin et aL, 1989). Analyses Proteins were determined by the Coomassie Brilliant Blue method (Bradford, 1976) using bovine serum albumin as a standard. DNA was analyzed by the fluorometric method using salmon DNA as a standard (Setaro and Morley, 1976). RNA was analyzed by precipitating the cellular fractions in 0.4 M HCIO4, followed by extraction of the precipitate in 0.4M HC104 for 18rain at 70°C. The absorbance of the extract was measured at 260 nm and RNA calculated on the basis of 34.2 absorbance units/mg of RNA. Glycogen was analyzed (Harris et aL, 1974) and expressed as mg glucose obtained after enzymic degradation of glycogen. Acid proteinase activity in skeletal muscle was determined in the supernatant obtained after centrifugation for 30 min at 15,000g of the muscle homogenate (Momm~n et aL, 1980). Hemoglobin was used as substrate and the tyrosine released was determined by a fluorescent method (Ambrose, 1974). The results are expressed as nag tyrosine released from hemoglobin/hr.
299
300
A. VON DER DECKEN
Table I. Body weight, liver and gonadal wet weight as % of body weight and blood plasma proteins in non-spawning and spawning salmon Per ml of plasma Fish Body weight HSI* GSl? Protein (mg) Vitellogenin (rag) Non-spawning (14) Spawning (21)
2875 5: 240" 2660 5: 200"
1.16 _+0.04* 1.26 5:0.03 b
0.51 5:0.05 s 1.13 5:0.06 b
43.02 _+2.12' 53.11 5:3.45 b
< 10- 3, 9.57 5:1.69 b
*Liver wet weight as % of body weight; ?gonadal wet weight as % of body weight. The results are the means 5: SEM. The numbers of fish are given in parentheses. Means with different superscript letters within a column are significantly different, P < 0.05. Table 2. Content of protein, DNA, and sarcoplasmic and myofibrillar protein and RNA in the muscle of non-spawning and spawning salmon Per g wet weight of muscle RNA (rag)
Protein (mg) Fish Non-spawning Spawning
Total
Sarcoplasmic
MyofibriUar
Sarcoplasmic
Myofibrillar
DNA (rag)
129.3 + 3.3' 116.8 + 3.6b
60.2 + 1.7' 53.4 + 2.5b
65.1 + 2.0' 65.0 + 2.0'
0.369 + 0.012' 0.285 + 0.009 b
0.388 + 0.012" 0.336 + 0.009b
0.747 + 0.025' 0.661 + 0.025 b
The results are the means + SEM of 10 fish per group. Means with different superscript letters within a column are significantly different, P < 0.05.
Statistical evaluation
DISCUSSION
The results are expressed as means + SEM. Data were analyzed using one-way analysis of variance followed by Student's t-test (Snedecor and Cochran, 1980).
RESULTS
Table 1 shows that the weights of liver and gonads per 100 g body weight (hepato- and gonadosomatic indices) were significantly higher in the spawning group compared with the non-spawning fish of similar age and body weight. The maturation process was noticeable also as a mg level of vitellogenin in the plasma and an elevated plasma protein content (Table 1). Total protein content per g wet weight of muscle decreased in the spawning group (Table 2). The decrease was confined to the sarcoplasmic and not the myofibrillar proteins. With the decrease in total protein and the unchanged myofibrillar protein content the protein myosin heavy chain was expected to rise per mg of total protein. Myosin heavy chain/mg of total protein was 0.225+0.010 and 0.240 + 0.009 for the non-spawning and the spawning group, respectively. The differences between the groups were not significant. RNA content was diminished by 23% in the sarcoplasmic and 13% in the myofibrillar fraction of the spawning group, and the level of DNA per g wet weight increased significantly (Table 2). The event of spawning evoked a 1.7-fold increase in acid proteinase activity, and a significantly increased accumulation of glycogen by 25% (Table 3). Table 3. Glycogen content and acid proteinase activity in the muscle of non-spawning and spawning salmon Fish Non-spawning Spawning
Per g wet weight of muscle Acid proteinase activity* Glycogen? 0.254 5:0.008 s 0.442 + 0.016b
6.49 5: 0.27' 8.17 5:0.21 b
*Acid proteinase activity is given as mg tyrosine released from the added substrate hemoglobin per hour. ?Glycogen is expressed as mg glucose. The results are the means + SEM of 10 fish per group. Means with different superscript letters within a column are significantly different, P < 0.01.
The major differences in epaxial muscle constituents between non-spawning and spawning females in the absence of migration were focused on the proteins and RNA of the sarcoplasmic fraction, protein degradation, glycogen and DNA content, as well as the expected rise in plasma vitellogenin and protein levels. The elevated DNA content per g wet weight of muscle in the spawning group suggested a diminished amount of other constituents. During the shift from sea to fresh water the moisture content of muscle decreases by 4% (Cowey et al., 1962). This would not be sufficient to account for the 13% increase in DNA in the spawning females. The rise in DNA could partially be attributed to the decline in sarcoplasmic proteins. The lipid content of muscle decreases drastically during spawning migration (Love, 1970; Ando et al., 1985; Sargent et al., 1989). It has been reported that an inverse relationship exists between the lipid and water content of the fish whereby catabolized lipid is replaced by an equal volume of water (Sargent et al., 1989). If the water is retained in muscle its moisture content will increase, and the loss of lipids cannot be made responsible for the apparent rise in DNA observed here. In Oncorhynchus nerka not all the lipids in muscle are used for energy purpose (Idler and Bitners, 1960). Part of the lipids are transferred from muscle to the gonads and therefore are not replaced in muscle by catabolic water from the lipids. In the Argentine hake (Merluccius hubbsi) energy content in muscle decreases during the period of gonadal growth confirming an energy transfer from one tissue to another (Montecchia et aL, 1990). The elevated level of muscle glycogen indicated that the carbohydrate was not utilized as a major energy source during the maturation-spawning season. The rise in glycogen pointed towards an increased uptake of glucose, as gluconeogenic enzyme activities in fish muscle appear to be low (for review see Suarez and Mommsen, 1987). It has been reported that acid proteinase activity increases during spawning migration of salmon (Mommsen et ai., 1980; Ando et ai., 1986). A close relationship between proteinase activity and the hormone condition of fishes has been demonstrated (Ando et al., 1986). When immature salmon is treated with 17-~ estradiol acid proteinase activity is elevated
Spawning and non-spawning female salmon (Olin et al., 1991). In the present work acid proteinase ' activity increased in the spawning group and might have led to the diminished content of the sarcoplasmic proteins. These results support the notion that protein degradation in muscle is related to the process of maturation and spawning. However, the physical activity of upstream migration will add to the event of protein degradation (Ando et aL, 1986). The sarcoplasmic reticulum controls the relaxation-contraction mechanism of muscle by controlling Ca 2+ levels in the sarcoplasm. R N A content is an indirect measure of the capacity for protein synthesis. The decrease in concentration observed in the sarcoplasmic fraction suggested a fall in protein synthesis activity leading to the conclusion that the sarcoplasmic protein content was affected by a low synthesis as well as an elevated degradation (Ando et al., 1986). The diminished R N A content of the myofibrillar fraction suggested a decrease in protein synthesis activity. The moderate but significant changes observed in muscle were insufficient to explain the inability of the non-spawning females to trigger the events of vitellogenesis. Maturation and spawning did not influence the physiological functions of muscle to such an extent as would lead to the often-occurring death observed after spawning. The additional load of upstream migration of the fish is required to evoke pronounced changes in muscle and impair the metabolic processes of the body. In conclusion, in the absence of upstream migration, maturation and spawning together led to changes in muscle constituents which were controlled by the metabolic processes of reproduction. In contrast to the myofibrillar cell compartments, the sarcoplasmic constituents responded readily to the metabolic demands of maturation and spawning. Bearing in mind the upstream migration that occurs under natural conditions in the wild, the myofibrillar proteins must be saved to later support the physical exertion during the migratory journey. Acknowledgements--The work was supported by the Swedish Council for Forestry and Agriculture, Project No. 0851/89 V 82:3. The Center for Environmental Research in UmeA, Sweden, supported the farming and feeding of the fish. The competent technical assistance of Ms Solveig Sundberg is gratefully acknowledged.
REFERENCES
Ambrose J. A. (1974) Fluorometric measurement of tyrosine in serum and plasma. Clin. Chem. 20, 505-510. Ando S., Hatano M. and Zama K. (1985) Deterioration of chum salmon (Oncorhynchus keta) muscle during spawning migration. I. Changes in proximate composition of chum salmon muscle during spawning migration. Comp. Biochem. Physiol. 80B, 303-307. Ando S., Hatano M. and Zama K. (1986) Protein degradation and protease activity of chum salmon
301
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