Dietary lipid and carbohydrate interactions: implications on growth performance, feed utilization and non-specific immunity in hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂)

Abstract

The present study was conducted to explore the effects of dietary lipid, carbohydrate and their interactions on growth performance, feed utilization, body composition and non-specific immunity of hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂). Nine isoproteic diets were formulated with three levels of dietary lipid (7, 10 and 13%) and carbohydrate (8, 12 and 16%) in a 3 × 3 factorial design. Triplicate groups of 30 juvenile fish (initial weight, 21.48 ± 0.24 g) were fed each of the diets twice daily to apparent satiation for 8 weeks. Results showed that a significant interaction between dietary lipid and carbohydrate was observed in the specific growth rate (SGR), and the SGR of grouper was not affected by dietary lipid but decreased significantly with the increase of dietary carbohydrate. Thereinto, grouper fed the diet containing 10% lipid and 8% carbohydrate obtained the highest SGR. Higher dietary lipid or carbohydrate significantly decreased feed intake (FI), but significantly elevated feed efficiency ratio (FER) and protein efficiency ratio (PER). Additionally, the retention rate of protein (PRR) and lipid (LRR) were both significantly improved with increasing dietary lipid level, while LRR was significantly decreased as dietary carbohydrate content increased. Meanwhile, significant interactions between dietary carbohydrate and lipid occurred in feed utilization. The apparent digestibility coefficient (ADC) of starch was significantly reduced with the increase of dietary lipid or carbohydrate level, and the interaction was also significant. With grouper fed the diet with 8, 12 and 16% carbohydrate, the postprandial glucose content peaked at the 3, 6 and 12h time-points, respectively. The activity of serum lysozyme increased significantly with the increase of dietary lipid, but significantly decreased as dietary carbohydrate content increased, while it was not significantly affected by the interaction. In addition, grouper fed the diets with 10% lipid obtained the highest SOD activity, in which no significant difference was observed with the increase of dietary carbohydrate content. In above, a combination of 10% lipid and 8% carbohydrate in the diet for this grouper should be optimum.