title: The effect of low temperature and fasting during the winter on metabolic stores and endocrine physiology (insulin, insulin-like growth factor-I, and thyroxine) of coho salmon, Oncorhynchus kisutch.
abstract: The objective of this study was to examine the effect of winter feeding and fasting at both high (10 degrees ) and low (2.5 degrees ) temperatures on growth, metabolic stores, and endocrinology of coho salmon. Treatments were as follows: warm-fed, warm-not fed, cold-fed, and cold-not fed during the winter (January-February). The following parameters were measured: length, weight, whole body lipid, liver glycogen, hepatosomatic index, and plasma levels of insulin, insulin-like growth factor-I (IGF-I), and thyroxine (T4). Warm-fed fish grew continuously throughout the experiment from 21.5 +/- 0.3 to 43.4 +/- 1.4 g and were larger than fish in the other treatments. Fish in all other treatments grew from 21.5 +/- 0.3 to approximately 32 g and showed depressed growth during January and February. During the winter, liver glycogen, hepatosomatic index, plasma insulin, and IGF-I were highly influenced by manipulations in rearing conditions, whereas whole body lipid and plasma T4 were less affected. Plasma insulin levels fluctuated dramatically (from 2 to 7 ng/ml) in the two cold-acclimated groups shortly after the change in temperature. In general, the plasma insulin levels of the warm-fed fish were the highest (8-9 ng/ml), those of the warm-not fed fish were the lowest (2-5 ng/ml), and those of the two cold-acclimated groups were more variable but intermediate. In contrast, plasma IGF-I levels showed a decline with temperature decrease (from 9 to 5 ng/ml) and more gradual changes than insulin with the change in feeding. The highest plasma IGF-I levels were found in the warm-fed fish (10-15 ng/ml), the lowest levels were in the cold-not fed fish (4-5 ng/ml), and those of the warm-not fed and cold-fed fish were intermediate. During the treatment period the T4 levels were relatively unaffected by manipulations in feeding and temperature compared with either insulin or IGF-I. These data suggest that the insulin, IGF-I, and thyroid axes are differentially regulated under changing seasonal and/or environmental conditions in yearling salmon.
authors.affiliation: Integrative Fish Biology Program, Northwest Fisheries Science Center, National Marine Fisheries Service, 2725 Montlake Boulevard, East Seattle, Washington 98112, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Larsen
authors.forename: B R
authors.initials: BR
authors.lastname: Beckman
authors.forename: W W
authors.initials: WW
authors.lastname: Dickhoff
mesh_terms: D000818:Animals; D001699:Biometry; D001835:Body Weight; D003080:Cold Temperature; D005215:Fasting / Q000502:physiology*; D006003:Glycogen / Q000378:metabolism; D006728:Hormones / Q000097:blood*; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D050356:Lipid Metabolism; D008099:Liver / Q000378:metabolism; D017684:Oncorhynchus kisutch / Q000033:anatomy & histology / Q000502:physiology*; D012621:Seasons; D013974:Thyroxine / Q000097:blood
chemical_list: D006728:Hormones; D007328:Insulin; D007334:Insulin-Like Growth Factor I; D006003:Glycogen; D013974:Thyroxine