Correlation analysis of fish growth performance and serum hormone and digestive enzyme activities of juvenile pearl gentian grouper (Epinephelus lanceolatus♂×E. fuscoguttatus♀) fed with different protein levels diets

An 8-week feeding trial was conducted to assess the correlation of the dietary protein with growth of juvenile pearl gentian grouper (Epinephelus lanceolatus♂×E. fuscoguttatus♀), serum hormone and digestive enzyme activities, to explore the effects of dietary protein levels on healthy growth. Grouper average body weight (6.50±0.00) g were randomly divided into 6 groups with 4 replicates in each group. The fish were fed isoenergetic and isolipidic experimental diets with protein levels 35%, 40%, 45%, 50%, 55% and 60%, respectively. The results showed that weight gain rate and specific growth rate of the fish fed with 50% protein diet were significantly higher than those of fish fed other protein level diets. The concentrations of total protein (TP) in 50% group and 60% group were significantly higher than 35% group. The concentrations of growth hormone (GH) and insulin (INS) in 50% group were significantly lower than those in other groups. The highest insulin-like growth factors-Ⅰ (IGF-Ⅰ) concentration was found in 45% group and significantly higher than those in other groups. Pepsin and intestinal trypsin activities in 50% group were significantly higher than those in other groups. With increasing dietary protein levels, intestinal amylase activity was decreased, the lowest value was found in 55% group and 60% group and significantly lower than those in other groups. There was extremely significantly negative correlation between WGR and GH. According to these results, based on broken-line regression analysis of WGR, a diet containing 51.57% protein is recommended for efficient growth of juvenile pearl gentian grouper.