Effect of dietary lipid level on growth, feed utilization and body composition of juvenile giant croaker Nibea japonica

• 8.22% dietary lipid level was appropriated for Nibea japonica.
• 9–13% dietary lipid level could improve the protein utilization.
• 13–21% dietary lipid led to a lipid accumulation in visceral organs.

Five isoproteic diets were designated to investigate the effects of dietary lipid levels (from 5% to 21%) on the growth performance, body composition and nutrition utilization of juvenile giant croaker, Nibea japonica (initially weighing, 6.67 ± 0.18 g per fish). Each diet was fed to triplicate tanks (15 fish per tank) for 8-weeks. Fish fed diets with low lipid levels (5–13%) showed significantly higher weight gain (WG) and special growth ratio (SGR) than those fed high lipid diets (17–21%) (P < 0.05). A decreased trend of feed intake (FI) and daily feed intake (DFI) was observed in Nibea japonica fed diets with lipid level from 5% to 21%. Diets with 9–13% lipid level could improve the protein utilization in this species. Fish fed diets with 5% and 9% lipid level had significantly lower viscerosomatic index (VSI), hepatosomatic index (HSI) and intraperitoneal fat ratio (IPF) than those fed with high lipid diets (13–21%) (P < 0.05). Fish fed diet with lowest lipid level showed significantly lower whole body lipid level than other treatments (P < 0.05). The liver lipid content had a trend to increase with dietary lipid level increased (P < 0.05), while liver protein and moisture level decreased with an increase in dietary lipid level (P < 0.05). Based on the second order polynomial regression analysis of WG, this study suggested that 8.22% dietary lipid level was appropriated for N. japonica.