Effects of dietary protein and lipid levels on growth, feed utilization and body composition in juvenile goldfish, Carassius auratus

An 8-week feeding trial was conducted to determine the optimum dietary protein and lipid levels for growth, feed utilization and body composition of goldfish, Carassius auratus juveniles (1.66 ± 0.018 g). Six diets containing two protein levels (300 and 400 g/kg) and three lipid levels (40, 80 and 120 g/kg) were formulated. Fifteen fish were randomly allotted to 18 aquaria (0.6 × 0.3 × 0.45 m) and fed to apparent satiation. The results showed that weight gain and specific growth rate (SGR) increased in response to higher dietary proteins with highest weight gain and SGR recorded in diet containing 400 g/kg protein with 80 g/kg lipid. Both feed intake (FI) and protein efficiency ratio (PER) were dependent on dietary protein and lipid level (P<0.05). Lipid retention (LR) was negatively correlated while hepatosomatic index (HSI) and viscerosomatic index (VSI) was positively correlated with dietary lipid levels. Whole body protein content decreased (P<0.05) while, lipid content increased with increasing dietary lipid at each protein level. Second-order polynomial regression also revealed diet containing 400 g/kg protein level and 80 g/kg lipid level optimal for the growth and feed utilization of juvenile goldfish, C. auratus.