Long-term supplementation of exogenous bile acids enhanced growth efficacy, hematology, non-specific immunity, and intestinal histomorphology, with significant liver dysfunction in Nile tilapia fingerlings

A 16-week feeding trial was conducted to examine the effects of dietary exogenous bile acids (BAs) on growth performance, digestive enzyme activities, biochemical indices, antioxidant capacity, non-specific immune response, gene expression of proinflammatory cytokines, and liver and intestinal morphology in Nile tilapia (initial weight, 5.10 ± 0.22 g) reared in earthen ponds over an extended period. Two isonitrogenous (31.65% protein) and isolipidic (4.71%) experimental diets were formulated by adding a control diet (BA0) and 0.25 g bile acid per kg diet (BA0.25), respectively. The diets were randomly assigned to 6 hapas, each stocked with 20 fish and fed for 16 weeks. Supplementing with BA0.25 significantly enhanced growth metrics and intestinal digestive enzyme activities compared to BA0. Hematological analysis showed increased levels of white blood cells (WBC), lymphocytes, and neutrophils in the BA0.25 group compared to the control. Additionally, respiratory burst activity, phagocytic activity, and serum lysozyme activity were notably higher in fish fed BAs at 0.25 g kg− 1. Antioxidant parameters (SOD, CAT, GSH) were elevated, and the expression of the proinflammatory cytokine IL1β was downregulated in intestinal tissue from the BAs-supplemented group. Significant improvements in intestinal histomorphometry were observed in the BAs-supplemented group. BAs supplementation altered intestinal microbial composition, increasing total and Pseudomonas counts while reducing coliform levels. Interestingly, glucose, triglycerides, cholesterol, serum hepatic markers (ALT, AST, and ALP), hepatic oxidative MDA levels, and proinflammatory IL1β mRNA expression increased markedly in the supplemented-BAs group, while activity of antioxidant enzymes (SOD, CAT, GSH) and HSP70 mRNA expression were notably diminished. Moreover, significant alterations were shown in the hepatic tissue of the BAs-supplemented group. Consequently, dietary supplementation with bile acids for a prolonged period improves growth, intestinal health, and immunity; however, it harms the liver health of Nile tilapia.