Effects of the replacement of fishmeal by soy protein concentrate on growth performance, apparent digestibility, and retention of protein and amino acid in juvenile pearl gentian grouper

Soy protein concentrate (SPC), as a protein source, is widely used to replace partial fish-meal (FM) in aquafeeds, especially for carnivorous fish. This study investigated the effects of partial FM replacement by SPC for juvenile pearl gentian grouper. The fish were fed with diets containing six levels of SPC (SPC 0, 15, 30, 45, 60, and 75) for 6 weeks. At the end of the feeding trial, average body weight gain (BWG), specific growth ratio (SGR), and weight gain ratio (WGR) had the highest values in fish fed with diet SPC 15, followed by that of fish fed with SPC 0 while fish fed with SPC 75 had the lowest values (P < 0.05). Fish fed with diet SPC 15 and SPC 30 had the highest protein efficiency ratio (PER) while fish fed with diet SPC 15, SPC 30, and SPC 45 had the highest feed conversion ratio (FCR) (P < 0.05). Daily feed intake (DFI) was significantly decreased in fish fed with diets containing any level of SPC (P < 0.05). Survival rate was significantly higher in fish fed with diets SPC 15, SPC 30, and SPC 45 as compared to other treatments. Fish fed the diet including less than 30% FM replacement showed a higher protein content in the muscle. The ADC of dietary protein and some amino acids were significantly higher in diets SPC 0, followed by SPC 15; while SPC 75 had the lowest content (P < 0.05). Similarly, fish fed with SPC 30 and SPC 15 showed significantly higher protein and amino acid (AA) retention than other dietary treatments. The optimal FM replacement with SPC for specific growth ratio (SGR) was estimated to be 14.41% using a non-linear higher order regression model. These results indicated that pearl gentian grouper has a limited ability to utilize SPC as a protein source, and the FM replacement with SPC should be less than 30% (FM45.5 g 100g(-1) and SPC18g 100g(-1)).