A new insight on the application of phytosterols in the aquatic feed: Improve the growth and intestinal health of largemouth bass (Micropterus salmoides) fed the high starch diet.

This study investigated the effects of phytosterols (PS) supplementation in high-starch diets on growth, antioxidant capacity, muscle/intestinal morphology, and gut microbiota in largemouth bass (Micropterus salmoides). A total of 960 fish (11.14 ± 0.48 g) were divided into six groups (Control, 8 % starch; HC, 13 % starch; HCP1-HCP4: HC + 0.025 %/0.05 %/0.075 %/0.1 % PS) for an 8-week feeding trial. Compared to the HC diet, dietary supplementation of 0.05 % PS significantly enhanced the growth and anti-oxidative ability of largemouth bass, as well as reduced MDA concentration and suppressed digestive enzyme activities. PS supplementation improved intestinal health by increasing muscle fiber density and intestinal fold width, also up-regulated the expression of bcl-2, claudin-1, claudin-4, and mef2d while downregulated the expression of murf1, atrogin1, and mstn (P < 0.05). PS modulated apoptosis by elevated BAD protein fluorescence intensity while reduced BCL-2 and CASPASE-3 protein fluorescence intensity (P < 0.05). Additionally, compared to HC diet, dietary supplementation of 0.05 % PS increased Firmicutes abundance and decreased Proteobacteria abundance. These findings demonstrated that 0.05 % PS supplementation in HC diets improved growth performance, muscle quality, antioxidant capacity, intestinal integrity, and beneficial microbiota composition of largemouth bass.