Effects of dietary lipid-to-carbohydrate ratio on growth and carbohydrate metabolism in juvenile cobia(Rachycentron canadum)

This experiment was conducted to investigate the effects of dietary lipid-to-carbohydrate ratio on growth and carbohydrate metabolism in juvenile cobia(Rachycentron canadum).Six iso nitrogenous diets were prepared to vary in lipid-to-carbohydrate ratio(g/g) as follows:Dl,2.26;D2,1.31;D3,0.78;D4,0.47;D5,0.34;and D6,0.23.Cobias were fed to satiety for 8 weeks.The weight gain and protein efficiency ratio in Dl group were significantly lower than those in other groups(P <0.05),accompanied by a lower level of feed conversion ratio(P <0.05).Protein retention efficiency in D4 and D6 and whole body protein in D4 and D5 were significantly higher than those in D1 group(P <0.05).Survival rate in D4 group was the highest among all groups and was significantly higher than that in Dl,D2 and D5(P <0.05).In terms of serum triglyceride,D1 and D2 were significantly higher than D6(P <0.05).Hepatosomatic index in D3 and D4 was significantly lower than that in D1(P <0.05).Fructose-1,6-diphosphatase in D4 was significantly higher than that in D1 and D3(P <0.05).Phosphofructokinase in D3 and D4 and malic enzyme in D4 and D5 were significantly higher than those in other groups(P <0.05).Results indicate that cobia utilizes carbohydrates as energy source more efficiently than it utilizes lipids.The optimal lipid-to-carbohydrate ratio in juvenile cobia diets is 0.47.