Dietary surfactin supplementation improves the growth performance and intestinal health of juvenile American eels with two body sizes cultured in cement tanks

This study evaluated the effects of dietary surfactin at 100 mg/kg on the growth performance and intestinal health of juvenile American eels ( Anguilla rostrata ) reared in commercial cement tanks. The trial comprised three groups, each with three replicate tanks. The body weight of trial fish in both the Control-W20 group and the Surfactin-W20 group was about 20 g/fish, and it was about 40 g/fish for the trial fish in the Surfactin-W40 group. The feeding trial lasted for 12 weeks. Dietary surfactin significantly increased final body weight, weight gain rate, and feed efficiency in juvenile American eels. Surfactin supplementation enhanced intestinal lipase activity, elevated the activities of superoxide dismutase and glutathione peroxidase, and increased glutathione content in the intestine. Dietary surfactin improved intestinal morphology, as indicated by increased villus length and muscular thickness ( P <0.05). The improvements in the above parameters were comparable between the Surfactin-W20 and Surfactin-W40 groups. Relative to the Control-W20 group, the Surfactin-W20 group exhibited an increased relative abundance of Bradyrhizobium , Curvibacter , and Blastococcus , and reduced relative abundances of Candidatus arthromitus ( P <0.05). Collectively, these findings demonstrate that dietary surfactin at 100 mg/kg can effectively improve growth performance and intestinal health in juvenile American eels under commercial cement‑tank conditions.