Macrogenomics-Based Analysis of the Effects of Artificially Compounded Diets on Spotted Seals (Phoca largha)

This study aimed to evaluate the effects of formulated diets on the composition and function of the gut microbiota in captive spotted seals. Six healthy spotted seals were selected and a self-controlled pre- and post-controlled design was adopted. They were initially fed chilled herring for one month (Group A), followed by one month of formulated diets (Group B). Fecal samples were collected, and 16S rRNA sequencing and metagenomics were used to analyze the microbiota structure, diversity, and functional potential. The results showed that after feeding with formulated diets, the relative abundance of Firmicutes and Bacteroidetes in the spotted seal gut significantly increased, while the proportion of Proteobacteria decreased. Principal coordinate analysis showed significant separation of the two groups in terms of microbiota structure. GO functional annotation showed that the formulated diet group had the most annotations in biological processes and molecular functions, but the fewest in cellular composition. KEGG pathway analysis indicated that formulated diets altered the nutrient metabolism and quorum-sensing pathways of the microbiota. In conclusion, formulated diets can regulate the gut microbiota structure of spotted seals and enhance some beneficial bacteria in the short term, but may also cause metabolic burden. Therefore, they are more suitable for short-term feeding, and long-term feeding requires further optimization of the formula to simulate natural nutrient composition.