Dietary phytosterol alleviates adverse effects caused by high-carbohydrate diets on growth performance, antioxidant capacity, glucolipid metabolism, and metabolomics in largemouth bass (Micropterus salmoides) juveniles.

High-carbohydrate diets (HCD) usually lead to metabolic syndrome in many fish species. However, the role of phytosterol (PS) in alleviating HCD effects on largemouth bass (Micropterus salmoides) is currently unknown. This study investigated the effects of dietary PS on growth performance, antioxidant capacity, histopathology, glucolipid metabolism, and metabolomics in juvenile largemouth bass fed a 5% corn-starch-enriched diet. Fish weighing 11.14 ± 0.48 g were fed a control diet (CON), a 5% corn-starch-enriched diet (HCD), and the same corn-starch-enriched diet supplemented with PS (0.025%, 0.05%, 0.075%, and 0.1%) in quadruplicate for eight weeks. The fish fed dietary PS increased significantly final body weight, weight gain, and specific growth rate (P < 0.05) compared with HCD. Moreover, fish fed dietary PS had significantly lower triglycerides and total cholesterol, while having higher high-density lipoprotein levels, than those fed HCD (P < 0.05). Feeding the fish on dietary PS improved hepatic superoxide dismutase and catalase activities, thereby lowering malondialdehyde content (P < 0.05). The fish fed dietary PS showed reduced hepatic lipid accumulation, increased interleukin-18 gene expression, and decreased interleukin-1β and tumor necrosis factor-alpha gene expression compared with those fed with HCD (P < 0.05). Furthermore, fish fed PS-supplemented diets significantly downregulated palmitic acid, choline, L-proline, and L-threonine metabolites compared with those fed HCD (P < 0.05). Our results demonstrate that dietary PS alleviates HCD-induced impairments by improving growth performance, antioxidant capacity, and glucolipid metabolites, thereby reducing lipid accumulation and inflammation in juvenile largemouth bass.