Optimal dietary protein levels for juvenile Pacific threadfin (Polydactylus sexfilis) fed diets with two levels of lipid

Abstract This study was designed to estimate the optimal dietary protein level for juvenile Pacific threadfin fed two levels of dietary lipid. Ten semi-purified diets were formulated to contain five levels of dietary protein (25, 30, 35, 40 and 45%) at either 10 or 14% dietary lipid. A commercial diet containing 14% lipid and 50% protein was fed as a reference treatment. Juvenile threadfin (initial body weight, 3.4 g) were hand fed these diets at 7% body weight/day for 8 weeks with 3 replications per dietary treatment. Fish were cultured in an indoor flow-through system with 31‰ seawater at 26 °C. There were 20 fish per replicate. The dietary lipid levels did not cause significant changes in growth performance or body composition (P > 0.05). In contrast, the diet with 25% protein resulted in significantly (P