Effects of dietary carbohydrate to lipid ratio on growth performance, body composition and serum biochemical indices of adult GIFT Oreochromis niloticus

To determine the optimal dietary carbohydrate to lipid (C/L) ratio for GIFT Oreochromis niloticus, we formulated six isonitrogenous and isoenergetic diets with C/L ratios of 1.53, 2.36, 3.55, 5.58, 9.85 and 21.82, respectively. Each diet had been randomly fed to the fish with initial average body mass of (218.33±11.03) g for 56 d. The weight gain rate (WGR) and specific growth rate (SGR) were the highest in group of 3.55, significantly higher than those in groups of 1.53, 9.85 and 21.82 (P<0.05). The feed efficiency (FE) and protein efficiency ratio (PER) in groups of 2.36−5.58 had insignificant difference, but were significantly higher than those in groups of 1.53 and 21.82. The viscerosomatic index (VSI) and hepatosomatic index (HSI) decreased significantly as the dietary C/L ratios increased (P<0.05), but the survival rate (SR) showed insignificant difference among different treatments (P>0.05). The whole body and liver lipid content decreased significantly as C/L ratios increased (P<0.05). The serum triglyceride (TG) and high-density lipoprotein cholesterol (HDL-C) levels decreased as dietary C/L ratios increased, whereas the low-density lipoprotein cholesterol (LDL-C) and glucose (GLU) contents showed an opposite trend (P<0.05). Based on the second-order polynomial regression analysis of WGR, PER and FE against dietary carbohydrate and lipid levels, the optimal C/L ratios were 4.19, 4.15 and 4.11, respectively. In conclusion, the diet with C/L ratio of 4.11−4.19 is optimal for adult GIFT O. niloticus.