Protein sparing effects in large rainbow trout, Salmo gairdneri

Abstract

Large rainbow trout (250–550 g) were fed to satiation or 0.5% live weight/day, one of six balanced diets varying in protein (30%, 43%, 52%) and lipid levels (12%, 24%). Growth and changes in body composition were measured over a 60-day feeding period. Mean appetite varied inversely with dietary digestible energy. Total weight gain over the 60-day period was not significantly different ( P = 0.05) for fish fed to satiation on diets containing 43 or 52% protein at the 24% lipid level. Weight gain was significantly lower among fish fed to satiation on the 30% protein, 12% lipid diet than those fed diets containing 43 and 52% protein, at either lipid level. When feeding level was limited to 0.5% of live body weight/day, weight gain was significantly higher for those fish fed diets containing 43 or 52% protein and 24% lipid, than fish fed all other diets. An increase in dietary lipid from 12 to 24% resulted in a significant increase in gross conversion efficiency of both dietary energy and protein, at all three dietary protein levels when fish were fed to satiation. A similar trend resulted when feeding level was reduced to 0.5% live weight/day. Dietary protein concentration did not significantly affect gross conversion efficiency of protein within either feeding rate. Increasing dietary protein tended to result in an increase in gross conversion efficiency of lipid at both dietary lipid levels within each feeding rate.