Effects of replacing dietary fish meal with fermented soybean meal, meat and bone meal and their mixture on growth, serum biochemical indices and intestinal histology of largemouth bass (Micropterus salmoides)

This study was conducted to investigate the effects of replacing fish meal with two protein sources individually or in combination on the growth performance, serum biochemical indices and intestinal histology of largemouth bass (Micropterus salmoides). Fermented soybean meal (FSM), meat and bone meal (MBM) and FSM + MBM mixture (1∶1) were used to replace 150 g/kg fish meal in the control diet containing 350 g/kg fish meal, and form four isonitrogenous and isolipidic diets. Then, the four diets were fed to M. salmoides with initial body weight of (21.2 ± 0.1) g for 8 weeks. The results showed that, compared with the control group, the weight gain (WG) in the three fish meal-replaced groups were not significantly different, but the WG in FSM group was lower than those in FSM+MBM group. Moreover, the feed conversion ratio of FSM group was significantly higher than that of the control and MBM groups. There were no significant differences in the whole body composition (moisture, crude protein, crude lipid and crude ash contents), dry matter digestibility, protein digestibility and protein retention among all the groups, but the protein efficiency ratio and lipid retention were decreased when substituting dietary FSM for fish meal. In terms of serum biochemical indicators, FSM group displayed higher aspartate aminotransferase activity as well as lower total antioxidant capacity, superoxide dismutase and lysozyme activity than those of the control group. In foregut morphology, the intestinal villus width was reduced in all the fish meal-replaced groups, but the villus height, muscle thickness and villus circumferences in FSM group were increased compared to the control group. Overall, in a diet containing 350 g/kg fish meal, MBM and FSM+MBM mixture could replace 150 g/kg fish meal without negative effects on the growth performance, nutrient utilization, antioxidant capacity, non-specific immunity and intestinal health, and FSM+MBM mixture showed better effects than FSM as substitutes for fish meal in the feed of M. salmoide.