Effects of seasonal temperature acclimatization on muscle metabolism in rainbow trout, Oncorhynchus mykiss

Maximal enzyme activities in cardiac and swimming muscles of rainbow trout (Oncorhynchus mykiss) were estimated during the natural progression of environmental temperature, between seasonal extremes of 4 and 18°C. Specific activity of marker enzymes were measured at a common temperature of 11°C to determine the potential for metabolic acclimatization. The results confirm an increased oxidative capacity in the cold, with little or no expansion in glycolytic capacity of slow muscle: citrate synthase (CS) activity was 23, 15 and 3 µmoles min^-1 g wet wt^-1 and pyruvate kinase (PK) 15, 23 and 17 µmoles min^-1 g wet wt^-1 from 4, 11 and 18°C acclimatized groups, respectively. Expansion of lipid metabolism was limited, with increased carnitine palmitoleoyltrasferase (CPT) seen only in the coldest group. Cardiac and fast muscle showed a similar response for CS but not PK or CPT which were greatest at 11 and 18°C, respectively. When compared with previous laboratory acclimation studies, these data suggest that environmental factors other than temperature are likely to influence the nature of metabolic acclimatization.