INDIVIDUAL VARIATION IN PROTEIN-TURNOVER AND GROWTH EFFICIENCY IN RAINBOW-TROUT, ONCORHYNCHUS-MYKISS (WALBAUM)

The aims of this study were to examine the relation between consumptio n, growth and protein synthesis for individual rainbow trout held in g roups, and to examine how differences in protein turnover may help to explain the observed differences in protein growth rate between rainbo w trout with Similar protein consumption rates. Therefore four measure ments of consumption were made for 37 individual fish over a 73 day pe riod by using radiography. At the end of the experiment, fractional ra tes of protein synthesis were measured by using a single flooding dose injection of [H-3]phenylalanine. The results showed that fractional r ates of protein growth and synthesis increased with consumption rate. However, degradation rates were independent of consumption. Fish consu ming similar amounts of food exhibited two- to threefold differences i n fractional protein growth rates, and twofold differences in fraction al rates of protein synthesis. Nine pairs of fish with similar protein consumption rates but different rates of protein growth were selected to examine if differences in protein metabolism, digestive efficiency or RNA concentration or activity could explain these observed differe nces in protein growth efficiency. More efficient fish were found to h ave reduced degradation rates; this was the only significant result ob tained. The results support the hypothesis that individual differences in protein turnover are important determinants of growth efficiency i n fish.