Effects of replacing fish meal with black soldier fly larvae meal on serum immune antioxidant indices, intestinal function and disease resistance of hybrid snakehead (Channa maculata ♀ × Channa argus ♂)

Fish meal is a prevalent source of animal protein in aquatic feed, yet its high cost and an import reliance of up to 80% have hindered the sustainable growth of aquaculture in our country. Thus, it is imperative to identify alternative proteins to replace fish meal. This study aimed to assess the impact of substituting fish meal with black soldier fly larvae meal (BSFLM) on the immune antioxidant status, intestinal flora and disease resistance of hybrid snakehead fish. Five isonitrogenous and isolipid diets were formulated, with fish meal replaced by 7.5% (BSFLM7.5), 15.0% (BSFLM15), 22.5% (BSFLM22.5) and 30.0% (BSFLM30) BSFLM, corresponding to 48.8, 97.6, 146.4 and 195.2 g/kg BSFLM, respectively. A total of 525 hybrid snakeheads with an average body weight of (10.84±0.01) g were randomly assigned to 5 groups, each with 3 replicates 35 fish per replicate. The results indicated that the alkaline phosphatase (AKP) activity in the BSFLM30 group was higher than in the BSFLM7.5 and fish meal (FM) groups (P<0.05). The malondialdehyde (MDA) levels in the BSFLM22.5 group were lower than those in the FM group (P<0.05). No significant differences were observed in the activities of lysozyme (LZM), catalase (CAT), superoxide (SOD), total antioxidant capacity (T-AOC), and glutathione peroxidase (GSH-Px) among all groups (P>0.05). The richness estimators Sobs, Chao, Ace, as well as Shannon and Simpson diversity indices of the intestinal content flora in the BSFLM15-BSFLM30 groups, were lower than those in the FM and BSFLM7.5 groups (P<0.05), indicating a decrease in species diversity. The relative abundance of Chlamydiae, Proteobacteria, Spirochaetes, Ralstonia and Pseudomonas in the experimental groups was lower than in the control group (P>0.05). Conversely, the BSFLM30 group exhibited higher Sobs, Chao, and Ace indices of intestinal flora compared to the FM and other experimental groups (P<0.05). The relative abundance of Bacteroidetes, Firmicutes, Paludibacter and Sedimentibacter was greater in the BSFLM30 group than in the other groups (P>0.05). The relative abundance of Spirochaetes, Proteobacteria and Ralstonia was lower in the experimental group than that in the control group (P>0.05). The mortality rate following Aeromonas schubertii infection was significantly lower in the BSFLM7.5, BSFLM7.5 and BSFLM22.5 groups than in the FM and BSFLM30 groups (P<0.05). In conclusion, dietary supplementation with BSFLM can enhance immune antioxidant capacity, microbial structure of intestinal contents, increase microbial diversity, improve intestinal function, and bolster resistance to A. schubertii infection. However, the replacement levels should not exceed 22.5%.