Dietary corn starch dose-dependently enhances intestinal and hepatic health in largemouth bass (Micropterus salmoides)

The study aimed to investigate starch-induced hepatobiliary syndrome in juvenile largemouth bass. Six isonitrogenous diets (Con, CoS20, CoS40, CoS60, CoS80, CoS100) with corn starch substituting 0 %, 20 %, 40 %, 60 %, 80 %, and 100 % of wheat starch, respectively, were tested over 70 days. Three replicates per group and 30 fish per net, totaling 540 fish with an initial weight of 10.48 ± 0.05 g, were used. The results indicated a significant difference ( P < 0.05) in growth with optimal at 41–59 % corn starch inclusion. Fish fed CoS20-CoS80 showed improved postprandial insulin and glucose regulation, a sustained glycemic response, and enhanced glycolytic activity compared to the fish fed the Con diet ( P < 0.05). Gut microbiota analysis revealed that Con-fed fish had reduced Firmicutes-to-Bacteroidetes ratios and increased Proteobacteria/Fusobacteria, indicating dysbiosis, while CoS60 promoted Firmicutes dominance for efficient carbohydrate fermentation and energy extraction. Liver antioxidant indices and serum biomarkers revealed that both Con and CoS100 induced metabolic stress and hepatic damage, while CoS40-CoS80 significantly improved them ( P < 0.05). Histology confirmed that Con-fed fish developed lipid accumulation, endothelial thickening, and inflammation, whereas CoS60 maintained liver health. Gene expression analysis confirmed a profound health benefit within the CoS40-CoS80 range, characterized by a significant down-regulated pro-inflammatory cytokine and NF-κB Pathway genes ( P < 0.05), and up-regulated Interleukin-10 (IL-10) and gut tight Junction integrity genes ( P < 0.05). Concurrently, the CoS40-CoS80 diets significantly promoted ( P < 0.05) hepatic lipid catabolism (up-regulation of peroxisome proliferator-activated receptor alpha (PPARα), Carnitine O-palmitoyltransferase 1 (CPT1), and adipose triglyceride lipase (ATGL)) and export (up-regulation of Microsomal triglyceride transfer protein (MTP)), while reducing cholesterol synthesis (down-regulation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR)). The CoS40-CoS80 range optimally balanced metabolic efficiency, microbiota composition, and hepatic function while reducing oxidative stress. These findings demonstrate that partial (41–89 %) corn starch substitution for wheat starch improves metabolic homeostasis and health outcomes in largemouth bass aquaculture. • Only wheat or corn starch diets impair liver function and cause stress in largemouth bass. • Moderate corn starch improves gut microbiota diversity and metabolic efficiency. • A 41–89 % corn starch range is ideal for bass health and farming. • 60 % corn starch optimizes bass metabolism, gut and liver health. • This research enables sustainable largemouth bass aquaculture through smart nutrition.