Effects of dietary carbohydrate level on growth and body composition of juvenile giant croaker Nibea japonica

An 8-week feeding trial was conducted to investigate the effect of dietary carbohydrate level on the growth performance, body composition of giant croaker, Nibea japonica. The six diets were designated as carbohydrate level from 0% to 30%. Each diet was fed to triplicate groups of 18 giant croaker (initially weighing, 7.40 +/- 0.15gfish(-1)) in flow-through sea water system. The weight gain (WG) and special growth ratio (SGR) had tendency to increase with carbohydrate level from 0% to 12% after that decreased, and significantly lower in fish fed diet with 30% carbohydrate level than in other groups. Moreover, fish fed diet with 30% dietary carbohydrate has significantly higher feed conversion ratio (1.48 +/- 0.18) and lower protein efficiency ratio (1.69 +/- 0.21) than other groups (P<0.05). The intraperitoneal fat ratio and condition factor had no significant difference in different groups (P>0.05), hepatosomatic index value increased with dietary carbohydrate increased (P<0.05). The result of this study also suggested that excess carbohydrate level (30%) led to lower lipid content in whole body. Based on the second-order polynomial regression analysis of WG and SGR, 12.2-12.7% dietary carbohydrate provided maximum growth of N.japonica.