Effect of dietary lipid levels on growth performance, body composition, and feed utilization of juvenile spotted knifejaw Oplegnathus punctatus

An 8-week feeding trial was carried out with various lipid level (2.30 %, 6.31 %, 8.98 %, 12.93 %, 16.08 %, and 18.99 %) diets to investigate the effects on growth performance, body composition, and feed utilization of juvenile spotted knifejaw Oplegnathus punctatus. After the feeding experiment, the weight gain (WG) and specific growth rate (SGR) significantly elevated with raising the dietary lipid level to 12.93 %, and then decreased when dietary lipid further increased (p < 0.05). The tendencies of feed efficiency (FE), protein efficiency ratio (PER), nitrogen retention (NR), and energy retention (ER) were consistent with the growth performance (p < 0.05). The lipid retention (LR) significantly decreased with dietary lipid increasing (p < 0.05). The fish consuming 2.30 % and 6.31 % lipid diets had significantly elevated hepatosomatic index (HSI) (p < 0.05). The intraperitoneal fat ratio (IPF) increased with the increase of dietary lipid levels (p < 0.05). The elevation of dietary lipid levels significantly increased the lipid concentrations in the whole body, dorsal muscle, and liver (p < 0.05). The highest liver glycogen deposition was found in the 2.30 % dietary lipid treatment (p < 0.05). The fish fed the diets added with 12.93 % lipid diet had the highest serum protein concentration (p < 0.05). The lowest total cholesterol (TC) content in the serum was detected in 2.30 % dietary lipid treatment (p < 0.05). The fish fed diets with 2.30 % or 18.99 % lipid obtained elevated serum AST and ALT activities (p < 0.05). The regression analysis in second order polynomial and two slope broken-line mode based on SGR and FE indicated that diet containing 10.46–12.83 % lipids was optimal for juvenile O. punctatus to obtain best growth performance and feed efficiency.