Assessing the effects of dietary live prey versus an artificial compound feed on growth performance, immune response, and intestinal microflora of largemouth bass Micropterus salmoides

The largemouth bass Micropterus salmoides is a carnivorous fish species that is widely farmed in China using artificial compound feeds. Alterations from its natural diet affect intestinal microbiota structure and growth performance and can reduce disease and stress resistance. In this study, we examined growth performance, immunity, intestinal microflora, and resistance to Aeromonas veronii infections-fed prey fish (PF) and artificial compound feed (ACF). Weight gains in the PF group were 27% significantly ( P < 0.05) greater than the ACF group. Antioxidant enzyme activities of superoxide dismutase, catalase, and glutathione peroxidase and mRNA expression of inducible nitric oxide synthase, transforming growth factor β1, and interleukin 10 were also significantly higher than for the ACF group. In contrast, levels of malondialdehyde were lower for the PF group consistent with the antioxidant activities. These results indicated that the commercial artificial compound diet reduced the immunity and anti-stress ability of the fish. Survival in against A. versonii infection were similar although the PF fish resisted the infection to a greater extent and succumbed at a slower rate. The gut microbiomes also differed between the PF and ACF feeding groups and operational taxonomic units were 1105.75 and 971.63, respectively. The high abundance of Verrucomicrobia were associated with weight gain and enhanced immunity for the PF group and were significantly ( P < 0.05) higher than that in ACF group. Bacteroidetes abundance was closely related to weight loss in the ACF group. The results of this study suggest that the changes in intestinal microflora structure caused by dietary changes in largemouth bass affected its growth performance and reduce its immune and anti-stress abilities and provide a theoretical basis for the improvement of largemouth bass compound feeds.