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 potential for offshore cage culture in tropical and subtropical waters. In the first trial, casein was added to a fish meal-based basal diet to replace starch to render protein concentration gradation ranging between 36% to 60%. All seven diets were estimated to be isoenergetic. After an 8-week growth trial, juvenile cobia (initial weight 33 g) fed the diets containing protein concentrations of 44%, 48% and 52% generally attained higher weight gain and feed conversion than the other groups. Polynomial regression analysis revealed 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 second trial, the cobia were fed seven isonitrogenous and isoenergetic test diets containing lipid concentrations ranging from% 3 to 18%. Growth of the fish (initial weight 41 g) was lowest when the dietary lipid concentration was 3%. Weigh gain increased with increasing lipid inclusion and then leveled off. The broken-line analysis that best expressed the response pattern shows 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 Elsevier Science B.V. All rights reserved.