Effects of a Mixed Bile-Acid Preparation on Growth Performance, Digestive Enzyme Activities, Gut and Liver Histology, and Expression of Lipid Metabolism-Related Genes in Asian Catfish (Clarias batrachus)

Bile acids (BAs) exert a dose-dependent, biphasic effect on growth performance in various fish species, acting as hepatoprotective and trophic agents at moderate levels, while becoming cytotoxic at higher concentrations. This study was conducted to assess the different levels of a mixed BA preparation on growth performance, digestive enzyme activities, gut and liver histology, and expression of genes involved in lipid metabolism in Asian catfish (Clarias batrachus). Three hundred and sixty juvenile Asian catfish were randomly distributed in eight groups in triplicate, and supplied with isonitrogenous (34.9% protein) and isolipidic (7.94%) diets containing different levels of exogenous mixed BA preparation at 0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, and 2.00 g/kg diet, for 90 days. Fish fed the diet with 0.75 g/kg BA had the highest weight gain and better feed-conversion ratio (p < 0.05) compared with the control. However, dose–response modeling establishes 0.87 g/kg BA as the mathematically derived optimum for maximizing somatic growth. The concentrations of serum total protein increased significantly with increasing BA level (p < 0.05). In fish fed the diet with 0.75, 1.0 and 2.0 g/kg BA, the activity of digestive lipase was significantly increased (p < 0.05), while the activities of digestive amylase and protease were unaffected by BA. At 0.75 g/kg dose rate, BA decreased (p < 0.05) activity of aspartate amino transferase and increased (p < 0.05) catalase activity. Gut and liver histology showed that BA level exceeding 0.75 g/kg induced pathological changes in both organs. Dietary BA supplementation upregulated the expression of lipid metabolism genes, including fxr, atgl, hsl, and cpt1, while downregulating srebp1, acaca, fas, and ppara in liver tissues. The present study demonstrates that dietary BA supplementation exerts a dose-dependent effect on growth performance, physiological status, tissue integrity, and metabolic regulation in Asian catfish. Supplementation at 0.75 g/kg feed optimizes growth and metabolic performance while avoiding toxic effects on the intestine and liver. However, excessive BA supplementation may compromise organ integrity, and should be avoided.