Effects of replacing fish meal with Bacillus aerobically fermented soybean meal on the growth performance, serum biochemical indices and intestinal histology of largemouth bass (Micropterus salmoides)

Abstract:

This experiment was conducted to study the effects of Bacillus aerobically fermented soybean meal (FSBM) on the growth performance, serum biochemical indices, and intestinal structure of largemouth bass (Micropterus salmoides). Five isoproteic and isoenergetic diets were formulated. A high fish meal (FM) diet containing 50% white fish meal was used as a control diet (0); FSBM was used to replace 10%, 20%, 30%, and 40% of the FM in the control diet to obtain the other experimental four diets. Largemouth bass [with initial body weight of (19.83±0.33) g] were randomly divided into five groups and reared in an indoor cage system for 75 d. Each group had 3 replicates, and each replicate contained 30 fish. The results showed that the weight gain rates of the 20% and 30% trial groups were significantly higher than that of the control group (P<0.05), but there was no significant difference in feed efficiency and survival rate in all experimental groups (P>0.05). There were no significant differences in either condition factor or hepatosomatic index between all trial groups (P>0.05); but the viscerosomatic index was significantly lower than that of the control group (P<0.05). There was no significant difference in serum albumin in all trial groups (P>0.05); the total protein and globulin of experimental groups were significantly higher than those of the control group (P<0.05); the serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities of the trial groups were significantly higher than those of the control group (P<0.05); In the 30% and 40% FSBM treatments, the intestinal muscular layer appeared thinner and villi integrity dropped. These results indicate that at least 20% of dietary FM protein in the diets of juvenile largemouth bass can be replaced by FSBM without having any adverse effect on growth performance, physical fitness, and intestinal health.