Abstract: Largemouth bass (Micropterus salmoides) frequently suffers hepatic metabolic disorders under intensive farming, and bile acids (BAs), as functional metabolic regulators, show variable effects depending on their composition and source. In order to investigate the regulatory effects of dietary C. idella bile acids on growth performance and hepatic metabolism of largemouth bass (Micropterus salmoides), three isonitrogenous and isolipidic experimental diets supplemented with 0, 150, and 300 mg/kg C. idella bile acids were formulated and fed to M. salmoides with an initial body weight of (16.21 ± 0.07) g for 8 weeks. Compared with the control group, dietary supplementation with 150 mg/kg C. idella bile acids significantly increased weight gain rate, reduced hepatic lipid accumulation, and decreased serum total cholesterol (TC) and aspartate aminotransferase (AST) levels. In addition, this supplementation level upregulated the hepatic expression of antioxidant-related genes (cat and gpx) and enhanced glutathione peroxidase (Gpx) activity. In contrast, no such beneficial effects were observed in the 300 mg/kg bile acid group. Furthermore, supplementation with 150 mg/kg C. idella bile acids markedly altered the serum bile acid profile, characterized by increased relative abundances of ursodeoxycholic acid (UDCA) and taurohyodeoxycholic acid (THCA), whereas the 300 mg/kg supplementation resulted in abnormal accumulation of chenodeoxycholic acid (CDCA). Hepatic transcriptomic analysis revealed that dietary supplementation with 150 mg/kg C. idella bile acids significantly activated growth- and stress-adaptive signaling pathways (including MAPK, Ras, and TGF-β pathways), while globally suppressing basal catabolic pathways such as PPAR signaling and fatty acid metabolism. Collectively, these results indicate that C. idella bile acids can promote growth performance, reduce hepatic lipid deposition, and enhance antioxidant capacity in M. salmoides by reshaping the host serum bile acid composition-particularly by increasing the proportions of UDCA and THCA-and thereby inducing systemic reprogramming of hepatic gene expression. Notably, these regulatory effects exhibit pronounced species specificity, providing new theoretical insights into the precision application of bile acids for modulating growth and metabolic health in aquaculture.