Methanotroph (Methylococcus capsulatus) bacteria meal, influences the intestinal microbiome, and improves intestinal barrier function and immunity in hybrid grouper (Epinephelus fuscointestinetatus ♀ × E. lanceolatus ♂)

Abstract

The hybrid grouper (Epinephelus fuscointestinetatus ♀ × E. lanceolatus ♂) is an important aquaculture marine species in China. The current study was designed to test the effects of methanotroph (Methylococcus capsulatus) bacteria meal (MBM) on hybrid grouper growth and intestinal health outcomes. Five iso-nitrogenous and iso-lipidic diets were formulated, comprising a control diet (MBM0) with 400 g/kg fish meal (FM) as the main protein source, and four experimental diets, in which FM was replaced at 5% (MBM2), 10% (MBM4), 20% (MBM8) and 30% (MBM12) with 20, 40, 80 and 120 g/kg of MBM, respectively. The 450 healthy juvenile hybrid grouper (initial weight 28.84 ± 0.05 g), were randomly allocated into five groups, with three replicates in each group and 30 fish in each replicate. They were fed for eight weeks prior to being sampled for transcriptome and microbiome research. The final body weight (FBW, P < 0.001) and weight gain rate (WGR, P < 0.001) were obviously enhanced in MBM2 and MBM8 groups compared to MBM0 group, and the specific growth rate (SGR) in the MBM2 and MBM8 groups were significantly enhanced compared to MBM0 group (P < 0.001). The condition factor (CF) in MBM4 and MBM8 groups were considerably reduced than that in MBM0 group (P = 0.008). The hepatic somatic index (HSI) in MBM8 and MBM12 groups were obviously enhanced than that in the other groups (P < 0.001). In the intestinal microflora analysis, the number of operational taxonomic units (OTUs) exhibited a significant linear increase with increasing MBM replacement ratio (P = 0.015). Concurrently, the richness of bacterial families and genera showed significant linear enrichment (P = 0.023 and P = 0.028, respectively). There was a decrease in the relative abundance of the potentially pathogenic genera Photobacterium and Vibrio in the MBM-fed group compared with the control group. The study has effectively shown that MEM may significantly enhance the health and growth of hybrid groupers by partially replacing FM in diets at the required amount of 3.70%, as determined by WGR regression analysis.