Rates of growth and protein synthesis correlated with nucleic acid content in fry of rainbow trout, Oncorhynchus mykiss: effects of age and temperature

Groups of recently hatched fry of rainbow trout, Oncorhynchus mykiss were maintained in the laboratory in order to investigate the effects of age, ration level and temperature on whole body growth, nucleic acid concentrations, protein synthesis rates and enzyme activities. In fry of up to 30 days after hatching, which were feeding but still had some yolk sac, no significant change in mean RNA concentration was observed with ration level. In older fry of 50 days or more, when the yolk sac was completely absorbed and exogenous feeding fully established, the concentration of RNA was correlated with the rate of protein growth. RNA concentrations and activities of citrate synthase and lactate dehydrogenase were significantly different between fed and starved fry. As water temperature was raised (from 5 to 15° C), higher rates of protein growth were brought about by an increase in the rate of protein synthesis and also by increased efficiency of retention of synthesized protein (reduced protein turnover). In fed fry, no change in RNA concentration was found with increasing temperature, while the amount of RNA per cell (RNA: DNA) decreased, indicating that increased rates of protein synthesis were due to increased RNA efficiency.