The effects of temperature acclimation on protein synthesis rates and nucleic acid content of juvenile cod (Gadus morhua L.)

Juvenile cod were acclimated to cold (5 °C) and warm (15 °C) water temperatures and fed sandeel at a similar ration size (3% body weight∙day −1 ) for at least 40 days. After this acclimation period, there were no significant differences in either weight-specific growth rate or weight-specific tissue protein synthesis rates (ventricle, gill, stomach, and intestine) between the cold- and warm-acclimated fish. However, every cold-acclimated tissue examined had a significantly higher RNA concentration (μg RNA∙g tissue −1 ) than the respective warm-acclimated tissue. Cold-acclimated ventricle and intestine had significantly reduced RNA activities (i.e., translational efficiency, g protein synthesized∙g RNA −1 ∙day −1 ) compared with the warm-acclimated tissues. In contrast, the mean RNA activities of cold-acclimated stomach and gill were not significantly different from those of the same tissues in the warm-acclimated fish. These alterations in RNA activity and RNA concentration with temperature acclimation probably represent a thermal compensatory mechanism for protein synthesis and growth in cod at 5 °C. Positive linear relationships were observed between tissue protein synthesis rates and tissue RNA concentrations (μg RNA∙g tissue −1 ). RNA/protein ratios (μg RNA∙mg protein −1 ) gave a positive (but statistically insignificant) trend with protein synthesis rates. In contrast, a negative trend (statistically insignificant) was observed between tissue protein synthesis rates and tissue RNA/DNA ratios (μg RNA∙μg DNA −1 ). The use of RNA measurements as biochemical correlates of growth rate in juvenile cod is discussed.