Optimal dietary protein and lipid levels for juvenile cobia (Rachycentron canadum)

Two growth trials were conducted to investigate the optimal concentrations of dietary protein and lipid for cobia, a pelagic fish showing great potent ial for offshore cage culture in tropical and subtropical waters. In the fi rst trial, casein was added to a fish meal-based basal diet to replace star ch to render protein concentration gradation ranging between 36% to 60%. Al l seven diets were estimated to be isoenergetic. After an 8-week growth tri al, juvenile cobia (initial weight 33 g) fed the diets containing protein c oncentrations of 44%, 48% and 52% generally attained higher weight gain and feed conversion than the other groups. Polynomial regression analysis reve aled a weight gain peak at a dietary protein concentration of 44.5%, which is regarded as the most suitable level for maximum fish growth. In the seco nd trial, the cobia were fed seven isonitrogenous and isoenergetic test die ts containing lipid concentrations ranging from% 3 to 18%. Growth of the fi sh (initial weight 41 g) was lowest when the dietary lipid concentration wa s 3%. Weigh gain increased with increasing lipid inclusion and then leveled off. The broken-line analysis that best expressed the response pattern sho ws a breakpoint when dietary lipid concentration was 5.76%. No significant growth enhancement was observed when the lipid levels were increased beyond the breakpoint to the highest lipid concentration tested (18%). (C) 2001 E lsevier Science B.V. All rights reserved.