Effect of Dietary Lipid Level on Growth Performance, Feed Utilization, and Body Composition of Juvenile Kelp Grouper Epinephelus moara

An 8-week feeding trial was conducted to assess the effects of different dietary lipid levels on the growth performance, feed utilization, and body composition of juvenile kelp grouper Epinephelus moara. Six diets with varying lipid levels of 2.82%, 5.30%, 7.83%, 11.76%, 14.19%, and 16.32% (designated as CL1 to CL6) were carefully formulated. A cohort of 324 juvenile fish (initial body weight of 5.87 ± 0.09 g fish−1) were randomly divided into six groups with three replicates in each group. The results showed that weight gain (WG) significantly improved as the dietary lipid level increased to 7.83%, followed by a decline with further increases. Fish fed the diet with 7.83% lipids also exhibited the highest feed efficiency (FE) and protein efficiency ratio. Although daily nitrogen intake and daily energy intake varied, no significant differences in nitrogen retention and energy retention were detected among the groups. With the increase in dietary lipid levels, daily lipid intake and daily lipid gain significantly increased, but lipid retention showed a consistent decline. Additionally, the viscerosomatic index and intraperitoneal fat ratio and the lipid content of the whole body, dorsal muscle, and liver increased significantly with increasing dietary lipid levels. The hepatic glycogen content inversely decreased with the elevation in dietary lipid levels. The lowest total cholesterol content in the serum was detected in the 16.32% dietary lipid treatment. According to the second-order polynomial regression analysis of WG and FE, a dietary lipid level of 6.56–9.31% was optimal for the growth performance and feed efficiency of juvenile kelp grouper.