Effects of adding essential amino acids to plant-based diets on growth performance, intestinal health and bile acid biosynthesis of grass carp (Ctenopharyngodon idella)

High-plant protein diets can present certain limitations for the growth and health of aquaculture species. By incorporating essential amino acids into grass carp feed based on amino acid balance, this study investigated their role in alleviating the previously mentioned challenges. The control diet consisted of soybean meal, rapeseed meal, and cottonseed meal as the major protein sources. In contrast, the experimental diet was fortified with 0.21 % lysine, 0.32 % methionine, and 0.23 % threonine. A total of 300 grass carp (61.3 g) were randomly allocated into six net cages and fed with either the control or experimental diet for eight weeks. The results demonstrated that dietary amino acid supplementation improved weight gain rate, specific growth rate, and feed efficiency (P < 0.05). Moreover, it downregulated the mRNA expression of the TLR/MyD88/NFκB signaling pathway and pro-inflammatory cytokines (P < 0.05), mitigating intestinal inflammation. Regarding the intestinal microbiota, this treatment increased ACE and Chao indices, accompanied by an elevation in the abundance of Firmicutes and a concomitant reduction in Spirochaetota and Brevinema (P < 0.05). Furthermore, the diet with amino acid supplementation increased hepatic sm transcript levels and cholesterol contents (P < 0.05). It also stimulated the mRNA expression of the cyp7a1, leading to elevated levels of hepatic cholic acid, taurocholic acid, taurochenodeoxycholic acid, and glycochenodeoxycholic acid 3 sulfate disodium salt and increased intestinal bile acid concentrations (P < 0.05). In summary, the essential amino acid supplementation reshaped the bile acid cycle of the host by promoting hepatic cholesterol and bile acid synthesis and influencing the composition of the gut microbiota, alleviated intestinal inflammation, and improved the growth of grass carp. The findings revealed that optimizing the amino acid balance in feed formulations can improve fish growth performance and health while lowering production costs, thereby supporting the sustainable advancement of the aquaculture sector.