Supplementation of tussah immunoreactive substances improves growth performance, innate immunity, and intestinal microbial homeostasis in the sea urchin Strongylocentrotus intermedius

The immunomodulatory effect of tussah immunoreactive substance (TIS) on aquatic animals has been confirmed, but its probiotic effects on the sea urchin Strongylocentrotus intermedius remains unclear. A feeding experiment was carried out to investigate the impacts of TIS on the growth performance, innate immunity and gut microflora of S. intermedius. The results showed that 0.5% and 1.0% TIS slightly increased specific growth rate and test diameter growth rate, while all TIS treatments significantly improved the gonadosomatic index (P < 0.05). In the 1.0% TIS group, total flavor amino acids in gonads increased by 5.4%, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) contents were elevated by more than 10%. Also, the immune enzyme activities varied and increased to different degrees among each TIS-treated group. Proteomics analysis indicated that TIS activated immune-related genes and upregulated pathways related to mitochondrial function and energy metabolism. 16S rRNA sequencing revealed that 1.0% TIS improved intestinal microbial diversity by enriching beneficial bacteria (Desulforhopalus and Ruegeria) and inhibiting harmful bacteria (Vibrio and Halarcobacter). In conclusion, dietary supplementation with TIS promotes growth, enhances immunity, and optimizes intestinal microbiota in S. intermedius. These results offer novel insights into the application of immunostimulants in sea urchin culture and contribute to the development of high-efficiency formulated feeds for sea urchins.