An evaluation of replacing fish meal with fermented soybean meal in the diets of largemouth bass (Micropterus salmoides): Growth, nutrition utilization and intestinal histology

A 56-day feeding trial was conducted to investigate the effects of replacing fish meal (FM) with soybean meal (SBM) and fermented soybean meal (FSBM) on growth performance, nutrition utilization and intestinal histology of largemouth bass. The basal diet contained 350 g/kg FM (control), and then, FM was replaced with SBM or FSBM of 15%, 30%, 45% and 60% respectively. The results showed that the specific growth rate of fish fed FSBM-60, SBM-45 and SBM-60 diets significantly decreased, and the feed conversion ratio of SBM-30, SBM-45, SBM-60, FSBM-45 and FSBM-60 groups increased when compared to the control group (p < .05). The apparent digestibility coefficients of dry matter and crude protein of SBM-45, SBM-60 and FSBM-60 groups were significantly lower than those of the control group (p < .05), and the substitution of FM with SBM and FSBM (45% and 60%) significantly reduced the protein retention (p < .05). Serum total protein contents of SBM-60 and FSBM-60 groups and serum cholesterol contents of SBM-45, SBM-60 and FSBM-60 groups were significantly lower than those of the control group (p < .05). The SBM-30 and SBM-60 groups showed significantly higher alanine aminotransferase activity than the control group (p < .05). The intestinal histology analysis resulted that the villus length of the SBM-60 group and the villus width of the SBM-45, SBM-60 and FSBM-60 groups decreased when compared to the control (p < .05). In conclusion, FSBM could replace 30% FM in diet of largemouth bass containing 350 g/kg FM, while the substitution level of FM with SBM was only 15%.