Effects of the amino acid mixture, ‘NutriMix’, on growth performance, non-specific immunity and intestinal health in sea cucumber (Apostichopus japonicus)

• NutriMix, a blend of lysine, methionine, and arginine, significantly boosts growth in sea cucumber Apostichopus japonicus . • Optimal dosage of NutriMix can enhance immune response and digestive enzyme activity. • NutriMix improves intestinal health and regulates gut microbiota in sea cucumber Apostichopus japonicus . In the present study, a mixture of amino acids (NutriMix) was used to evaluate its effects on growth performance, non-specific immunity and intestinal health in sea cucumber ( Apostichopus japonicus ). During a 56-day feeding trial, the sea cucumber (0.92 ± 0.05g) was fed with basal diet (control, CT) and treatment diets supplemented at different doses of amino acid mixture, 0.5‰ (AL), 1‰ (AM) and 2‰ (AH) (w/w, parts per thousand). The weight gain rate (WGR) and specific growth rate (SGR) of A. japonicus fed amino acid mixture were significantly increased in the AM group ( P <0.05). Additionally, the trypsin and lipase activities of the intestine were significantly increased in the AM group ( P <0.05). Analysis of the intestinal morphological features indicated that in the AM group, the intestinal structure of sea cucumber was more regular, longer, with intact intestinal villi, and with a complete muscular layer. Also, the muscle and mucosal layers are thicker. Alpha diversity analysis showed that the amino acid mixture-supplemented groups had higher intestinal microbial richness and diversity than the CT group. Furthermore, beta diversity analysis demonstrated distinct bacterial community structures between the amino acid mixture-supplemented groups and the control group, with Proteobacteria, Bacteroidota , and Verrucomicrobiota being the most abundant phyla. Notably, the AM group exhibited significant differences in intestinal microbiota composition, which may play a crucial role in the improved growth performance and health of A. japonicus . In conclusion, dietary addition of amino acid mixture could effectively promote the growth of A. japonicus , achieve cost-sparing effect in aquafeed, improve its digestion and immunity capacity to a certain extent, and actively regulate the intestinal microflora of A. japonicus .