Microbiome–Metabolomics Analysis Insight into the Effects of Starvation and Refeeding on Intestinal Integrity in the Juvenile Largemouth Bass (Micropterus salmoides)

The effects of starvation and refeeding on the gut condition of juvenile largemouth bass (<i>Micropterus salmoides</i>) remain unclear. Therefore, our research aimed to explore these effects. Amylase and lipase activities were remarkably decreased in the starvation (ST) group, yet prominently increased in the refeeding (RE) group (<i>p</i> < 0.05). In addition to the malondialdehyde (MDA) level, catalase (CAT) and superoxide dismutase (SOD) activities were significantly upregulated in the ST group (<i>p</i> < 0.05) in marked contrast to those in the controls; however, the RE group showed no substantial variations in CAT and SOD activities or the MDA level (<i>p</i> > 0.05). During starvation, the expression of Nrf2-Keap1 pathway-associated genes was significantly upregulated (<i>p</i> < 0.05). The comparative levels of TNF-α, IL-1β, and IL-15 were highly increased, with the levels of TGF-β1 and IL-10 apparently downregulated in the ST group; in contrast, these levels were restored to their original values in the RE group (<i>p</i> < 0.05). In contrast to the controls, the ST group showed significantly lower height and width of the villi, muscle thickness, and crypt depth and a higher goblet cell number; however, these values were recovered to some extent in the RE group (<i>p</i> < 0.05). The dominant bacterial phyla in the intestines of both groups were Proteobacteria, Firmicutes, Bacteroidetes, Acidobacteria, and Actinobacteria, with marked inter-group differences in the genera <i>Serratia</i> and <i>Lactobacillus</i>. Metabolomics analysis showed that amino acid metabolism is disrupted during starvation and is restored after refeeding. In summary, this study expands our comprehension of the interaction between oxidative stress and antioxidant defenses among juvenile largemouth bass subjected to starvation and refeeding.