The Investigation In Optimum Dietary Protein Requirement, Animal Protein To Plant Protein Ratio And Protein To Energy Ratio Of Siganus Guttatus

The propagation and culture of rabbitfish spring up rapidly in southeast China in recent years. Nevertheless, the investigation of rabbitfish nutrition requirement is still undeveloped and there is no feed which is produced to meet the nutrition demand of rabbitfish. It is urgent to investigate the nutrition requirement, and produce the environment-friendly and economical feed which can satisfy the different period requirement of rabbitfish. Siganus guttatus was chosen to be researched, mainly in optimum dietary protein requirement, animal protein to plant protein ratio and dietary protein to energy ratio in this study.A 49-day feeding trial was conducted to investigate the optimum dietary protein requirement of S. guttatus with the initial weight 105.04±0.49g. Five isoenergetic (17 MJ/Kg) diets with the protein concentrations 21%,30%,35%,39% and 48%, were fed to triplicate groups of 25fish. The growth performance of S. guttatus was significantly affected by the dietary protein level. Weight Gain (WG), Specific Growth Rate (SGR) and Protein efficiency ratio (PER) were maximized when fish were fed 35% dietary protein,15.70%,0.30%d-1 and 2.28%, respectively. Feed conversion rate (FCR) had an inverse correlation with increasing dietary protein level. Dietary protein concentration also had effects on body composition and biological indices. The whole body crude protein content accumulated slightly with increasing of dietary protein concentration. No significant differences were observed among all groups except D1. The highest muscle crude protein and the lowest muscle crude fat were both gained in D4. Liver crude protein and fat increased significantly with increasing dietary protein. Based on second-order polynomial regression model of SGR, the optimum dietary protein requirement for juvenile S. guttatus was determined to be 39.75%. In view of other parameters such as body composition and biological indices, it is suggested that the optimum dietary crude protein level of juvenile S. guttatus is between 35% and 39.75%.A 49-day feeding experiment was conducted to evaluate the effects of replacement of fish meal by soybean meal in S. guttatus (with the initial weight 104.64±2.76g) diets on fish growth performance, body composition and biological indices and to determine the optimum soybean meal concentration in S. guttatus diets. Five isonitrogenous and isoenergetic diets were formulated containing 35% protein and 19.00MJ/Kg gross energy. The replacement ratio (soybean meal:fish meal) was O:1(D1),1:2(D2),1:1(D3),2:1(D4), 1:0(D5). S. guttatus which were fed to satiate twice daily, were cultured in conical rearing tanks (0.5 m3) with 25ind per tank and three replications per group. The results showed that the growth performance of S. guttatus was significantly affected by the concentration of soybean meal in the diets. WG, SGR and FI had a negative correlation with diet soybean meal concentration. WG and SGR were maximized when fish were fed with pure fish meal,24.42%and 0.44%d-1, respectively. Significant differences were observed in SGR among each group. The value of FI in D1 was significant higher than that in D5. FCR had a positive correlation with diet soybean meal concentration. The lowest value of FCR was found in D1, but there was no significant difference between D1 and D2. There was also no obvious difference between D2 and D3.The replacement had no significant effects on muscle crude protein and moisture but had marked influence on whole body crude protein and fat. The lowest value of whole body crude protein was observed in D5 (19.11%). Liver crude protein content tended to increase firstly and then decrease, with increasing soybean meal concentration in diets. Liver crude fat in higher soybean meal concentration diets significant lower than in lower soybean meal concentration diets. The replacement had no significant effect on biological indices except Viscerasomatic index. The replacement ration should be less than 1:2 in S. guttatus diets based on SGR, FCR, FI and some other parameters. However, considering the muscle quality of S. guttatus, it is indicated that the replacement ration could amount to 2:1.A 49-day feeding experiment was conducted to evaluate the effects of dietary protein to energy ratio in S. guttatus (with the initial weight 105.25±0.86g) diets on fish growth performance, body composition and biological indices and to determine the optimum dietary protein to energy ratio in S. guttatus diets. Twelve diets with four different dietary protein concentrations and three different energy levels per dietary protein concentration were formulated. The protein concentration was 21%,30%,49% and 47% and the energy level was 4%,7% and 11%. The results showed that the dietary protein to energy ratio had a significant effect on growth performance, body composition and biological indices. It indicated that the optimum dietary protein to energy ratio in S. guttatus diets was 39/4 (93.67Cal/g). The dietary protein requirement in this trial was in line with our previous research that the optimum dietary requirement of S. guttatus.