Effects of Periodic Fasting and Refeeding on Enzyme Activities, Related Gene Expression and Gut Microbiota in the Sea Urchin Strongylocentrotus intermedius

Feeding strategy is a critical factor in sea urchin aquaculture. Previous studies have shown that the strategy of fasting for 3 days followed by refeeding for 9 days supports full compensatory growth in Strongylocentrotus intermedius, but the underlying mechanisms remain unclear. This study investigated the effects of periodic fasting and refeeding on enzyme activities, gene expression and gut microbiota in this species. Three feeding regimes were tested over 108 days: continuous feeding (group S0), fasting for 3 days followed by refeeding for 9 days (group S3), and fasting for 6 days followed by refeeding for 6 days (group S6). Group S3 had significantly higher digestive enzyme activities than group S0 (p < 0.05), with unchanged antioxidant enzyme activities. Intestinal genes related to nutrient processing and lipid synthesis (MYP, Elovl4, Tgfbi1, Tgfbi2) were upregulated in group S3. Gut microbiota alpha diversity was comparable across groups, but beta diversity showed significant structural remodeling in group S3, with an elevated Bacillota/Bacteroidota ratio and enriched Lutibacter and Desulfobulbia. By contrast, group S6 showed reduced digestive enzyme activities, downregulated expression of target genes in the intestine, elevated pro-inflammatory TNF-α transcript levels, and reshaped gut microbiota structure. In conclusion, the strategy of fasting for 3 days followed by refeeding for 9 days is associated with improved feed absorption efficiency and compensatory growth, accompanied by enhanced digestive capacity and up-regulated the expression of growth-related target genes in the intestine, and reshaped gut microbiota composition, providing a theoretical reference for intermittent feeding in S. intermedius aquaculture.