Effects of Dietary Protein and Lipid Levels on Growth Performance, Muscle Composition, Immunity Index and Biochemical Index of the Greenfin Horse-Faced Filefish ( Thamnaconus septentrionalis ) Juvenile

The effects of different dietary protein and lipid levels on juvenile greenfin horse-faced filefish ( Thamnaconus septentrionalis ) was experimentally evaluated in a 56-day study. Fish (initial weight 6.47±0.56 g) were fed with nine different diet combinations containing three varying levels of protein (37%, 43%, 49%) and lipids (4%, 7%, 10%) in triplicates, where the protein-to-energy (P/E) ratios of the diets varied in the range of 19.17–26.99 mg kJ −1 . Results showed that fish fed diets containing 49% protein and 10% lipid exhibited significantly lower feed intake than those fed other diets. The weight gain of fish fed diets with 43% protein was significantly higher than that of fish fed 37% or 49% protein diets. While no significant change in weight gain was observed when lipid content was increased from 4% to 7%, weight gain decreased significantly when lipid increased from 7% to 10%. The protein efficiency ratio and feed efficiency were highest when the fish were fed the diet with 49% protein and 7% lipids. Muscle crude lipid content was positively correlated with dietary protein level regardless of lipid level. The diet of 43% protein or 7% lipids significantly reduced the activity of alanine aminotransferase and aspartate aminotransferase in liver. The contents of aspartate aminotransferase, superoxide dismutase and malondialdehyde were significantly increased from 4% to 10% lipids in plasma. The plasma total cholesterol and triglyceride contents were positively correlated with dietary lipid level at the same protein level. Our comprehensive analysis concluded that a diet with 43% protein and 7% lipid, with a P/E ratio of 23.07 mg kJ −1 , significantly promote the growth performance, feed utilization and health of juvenile greenfin horse-faced filefish.