Effect of feeding different carbohydrate to lipid ratios on the growth performance and body composition of Nile Tilapia (Oreochromis niloticus) fingerlings

In this study, we evaluated the growth performance and body composition of Nile tilapia (Oreochromis niloticus) fed five isonitrogenous and isoenergetic diets (A, B, C, D and E) containing varying levels of carbohydrates (18.27-40.37%) and lipids (8.14-19.53%) with carbohydrate-to-lipid (CHO/LIP) ratios ranging from 4.95 to 0.94. Significant (P < 0.05) differences were observed in the body weight gain, condition factor, specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency ratio (PER), net protein retention (NPR) and apparent net energy retention (ANER) values of fish fed diets with different CHO/LIP ratios. The A, B and C diets with CHO/LIP ratios ranging from 4.95 to 2.06 did not result in any difference (P > 0.05) in fish performance. Decreasing the CHO/LIP ratio to 1.38 (diet D) significantly (P < 0.05) reduced growth rate and feed efficiency. A further decrease in the CHO/LIP ratio to 0.94 (diet E), however, did not affect (P > 0.05) these values any more. The hepatosomatic index (HSI) increased with a decrease in the CHO/LIP ratio and was the highest (1.81) with a CHO/LIP ratio of 0.94 and lowest (1.33) with a CHO/LIP ratio of 4.95. No significant (P > 0.05) differences were observed in the HSI values between the fish fed diets B, C and D with CHO/LIP ratios ranging from 3.33 to 1.38. The body compositions of the fish were significantly affected (P < 0.05) by different CHO/LIP ratios in the diets. Body moisture and crude protein contents decreased whereas fat and ash contents increased with decreasing CHO/LIP ratios. The CHO/LIP ratio in the diets did not, however, affect (P > 0.05) the gross energy content of the fish. The results of the present study indicate that the optimal dietary CHO/LIP ratio for a maximum growth performance of Oreochromis niloticus ranges between 2.06 and 4.95.