Effects of Dietary Carbohydrate-to-Lipid Ratios on Growth and Body Composition of Orange-spotted Grouper Epinephelus coioides

Growth performance of juvenile Orange-spotted Grouper Epinephelus coioides fed isonitrogenous (45% crude protein) and isoenergetic diets with varying carbohydrate-to-lipid ratios (0 to 10.9) were evaluated. Triplicate groups of 18 fish (initial mean individual body weight, 16.4 g/) were fed to satiety for 8 weeks. At the termination of this trial, significant differences (P < 0.05) were found on the growth performance. Weight gain and specific growth rate values increased with decreasing dietary carbohydrate-to-lipid ratios. The highest feed conversion ratio value and the lowest protein efficiency ratio value were observed in fish fed the 10.9 carbohydrate-to-lipid ratio diet. Besides, fish fed the 10.9 carbohydrate-to-lipid ratio exhibited the lowest nitrogen retention and energy retention values. With the diet carbohydrate-to-lipid ratios decreasing, hepatosomatic index values were reduced significantly (P < 0.001), while the intraperitoneal fat index values showed an inverse trend. Whole-body protein content was reduced with the decrease in dietary carbohydrate-to-lipid ratios, whereas whole-body lipid content increased significantly with decreasing dietary carbohydrate-to-lipid ratios (P < 0.001) while the whole-body moisture content showed a reverse trend. Additionally, liver lipid content increased with the decrease in dietary carbohydrate-to-lipid ratios, while contrasting results were found in liver glycogen content. The results of this study suggest that the suitable dietary carbohydrate-to-lipid ratio for Orange-spotted Grouper is 0.5 in the isonitrogenous (45% crude protein) and isoenergetic diets, and this species is better adapted to utilizing lipids rather than carbohydrates.