Probiotics Enhance Coilia nasus Growth Performance and Nutritional Value by Regulating Glucolipid Metabolism via the Gut–Liver Axis

Large-scale intensive feeding triggered reduced growth performance and nutritional value. Exogenous probiotics can promote the growth performance and nutritional value of fish through improving the intestinal microbiota. However, detailed research on the correlation between the intestinal microbiota, growth performance, and nutritional value remains to be elucidated. Therefore, we performed metagenomic and metabolomic analysis to investigate the effects of probiotic addition to basal diet (1.0 × 10⁸ CFU/g) (PF) and water (1.0 × 10⁸ CFU/g) (PW) on the growth performance, muscle nutritional value, intestinal microbiota and their metabolites, and glucolipid metabolism in <i>Coilia nasus</i>. The results showed that FBW, BL, and SGR were enhanced in PF and PW groups. The concentrations of EAAs, TAAs, SFAs, MUFAs, and PUFAs were increased in PF and PW groups. Metagenomic and metabolic analyses revealed that bacterial community structure and metabolism were changed in the PF and PW groups. Moreover, adding probiotics to diet and water increased SCFAs and bile acids in the intestine. The gene expression associated with lipolysis and oxidation (<i>hsl</i>, <i>pparα</i>, <i>cpt1</i>, and <i>acadm</i>) and glycolysis (<i>gck</i> and <i>pfk</i>) was upregulated, while the gene expression associated with lipid synthesis (<i>srebp1</i>, <i>acc</i>, <i>dgat</i>, and <i>elovl6</i>) and gluconeogenesis (<i>g6pca1</i>, <i>g6pca2</i>, and <i>pck</i>) was downregulated in the liver. Correlation analysis displayed that hepatic glucolipid metabolism was regulated through the microbiota-gut-liver axis. Mantel test analysis showed that growth performance and muscle nutritional value were improved by the gut-liver axis. Our findings offered novel insights into the mechanisms that underlie the enhancement of growth performance and nutritional value in <i>C. nasus</i> and other fish by adding probiotics.