Effects of dietary taurine supplementation on growth performance, serum biochemical responses, and intestinal health of juvenile American eel ( Anguilla rostrata )

This study evaluates the effects of dietary taurine on growth performance, serum biochemical indices, immune-related parameters, and intestinal health of juvenile American eel ( Anguilla rostrata ). 240 juvenile American eels were allocated to eight tanks (30 fish/tank; four replicate tanks/treatment) and fed a basal diet or the basal diet supplemented with 6 g/kg taurine for 10 weeks. 6 g/kg was selected basing on the lower bound of the 0.6-1.5% dietary taurine requirement range reported for carnivorous fish and yielding a total dietary taurine of approximately 0.738% when added to the calculated basal level (0.138%), close to the 0.79% estimated requirement for aquatic animals. Compared with the control, taurine supplementation significantly increased final body weight by approximately 4.1%, feed intake by 4.2%, and feed efficiency by 3.3%, with significant increases also observed in weight gain rate and specific growth rate ( P < 0.05). Serum immunoglobulin M concentration, activities of lysozyme, acid phosphatase, and alkaline phosphatase were significantly increased ( P < 0.05), whereas complement component 3 was unchanged. Serum D-lactate concentration, activities of alanine aminotransferase, aspartate aminotransferase, and diamine oxidase decreased significantly ( P < 0.05). Taurine also increased intestinal villus length and the thickness of the muscular layer ( P < 0.05). Alpha diversity indices were not significantly affected, whereas taurine supplementation regulated the taxonomic composition of the intestinal microbiota. At the phylum level, Firmicutes and Actinobacteriota tended to decrease, whereas LEfSe analysis identified Faecalibaculum and Vibrio as enriched taxa in the taurine group (LDA score > 3.0; P < 0.05). In conclusion, 6 g/kg taurine supplementation improved the growth performance, selected serum biochemical and immune-related parameters, and intestinal health of juvenile American eels. These preliminary findings suggest that the growth-promoting effect of taurine may be partly associated with enhanced immune-related responses, improved intestinal barrier-associated characteristics, and modulation of intestinal microbial composition.