Effect of various levels of lipid exchanged with dextrin at different protein level in diet on growth and body composition of juvenile flounder Paralichthys olivaceus

Abstract A 3 × 3 factorial experiment was conducted to determine proper levels of dietary protein, lipid and dextrin for juvenile flounder. Nine experimental diets were formulated to contain three protein levels (410, 460 and 510 g kg −1 ) and three lipid levels (60, 130 and 190 g kg −1 ) with corresponding dextrin levels (250, 150 and 50 g kg −1 ). Triplicate groups of fish (8.9 ± 0.4 g) were hand‐fed the diets to apparent satiation for 7 weeks in flow‐through system. Specific growth rate was the highest in fish fed the 510 g kg −1 protein diet with 60 g kg −1 lipid, and was not significantly different from that of fish fed 460 g kg −1 protein diet with 60 g kg −1 lipid. Feed efficiency ratio tended to increase as dietary protein level increased. The feed efficiency ratio of fish fed the 510 g kg −1 protein diets with 60–190 g kg −1 lipid levels was not significantly different from that of fish fed 460 g kg −1 protein diet with 60 g kg −1 lipid. Daily feed intake tended to decrease with increasing dietary lipid level at each protein level. Daily protein intake increased with increasing dietary protein level at 60 g kg −1 lipid level. Hepatosomatic index and visceralsomatic index increased with increasing dietary lipid level at each protein level. The lipid contents of liver, viscera and whole body, and concentrations of plasma total cholesterol and triglyceride increased with increasing dietary lipid levels; however, no significant difference was observed in the contents of dorsal muscle lipid. The results of this study suggest that the diet containing 460–510 g kg −1 protein with low lipid level (60 g kg −1 ) is optimal for growth and efficient feed utilization of juvenile flounder.