The response of grass carp (Ctenopharyngodon idella) juveniles to crude protein (CP) levels in practical diets was evaluated in an experiment with 120 juveniles and 80 days of feeding. The diets containing porcine meat meal, soybean meal, corn and wheat meal, with 22, 30, 36, or 44% CP. Ten juveniles (153.0±1.5 g) per tank (850L) were fed twice daily with pelleted feed (3% of biomass). Linear effect of CP on final weight, weight gain, specific growth rate, carcass and fillet yield, coefficient of protein retention, protein efficiency rate, deposition of fat and protein, and hematocrit were observed. It was also observed effect on triglycerides and total cholesterol in blood, indicating that dietary protein was being used as energy source. Feed conversion ratio and fat content in whole fish showed quadratic effect, with maximum points at 40.6 and 37.1% CP, respectively. The best CP content for grass carp in growing phase was 44%, and the variation of protein content in diet changed the metabolism of grass carp juveniles, reflected in blood and carcass parameters.
fish; Ctenopharyngodon idella; fat deposition; weight gain; blood parameters; growing phase
