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-degrees-C) and warm (15-degrees-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 (mug 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-degrees-C. Positive linear relationships were observed between tissue protein synthesis rates and tissue RNA concentrations (mug RNA . g tissue-1). RNA/protein ratios (mug 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 (mug RNA . mug DNA-1). The use of RNA measurements as biochemical correlates of growth rate in juvenile cod is discussed.