Growth Performance and Intestinal Health of Triploid Rainbow Trout ( Oncorhynchus mykiss ) Through Bile Acid Supplementation in Low Fishmeal Diets: Insights From Metabolomics, Microbiota, and Gene Expression

This research aimed to explore the impact of bile acid (BA) supplementation in low fishmeal diets on growth performance, serum biochemical indices, tissue morphology, lipid metabolism, gene expression, and gut microbiota in triploid rainbow trout ( Oncorhynchus mykiss , initial weight 15.97 ± 1.4 g). The experimental design involved a low fishmeal diet (10%), and four treatment groups with BA additions (0.05%, 0.10%, 0.15%, and 0.20%) to the basal diet. The findings indicated that the group receiving 0.10% BA (G3) exhibited an enhancement in final body weight (FBW), specific growth rate (SGR), weight gain rate (WGR), and condition factor (CF), significantly outperforming the control group (G1, p < 0.05). 0.10% BA addition significantly increased whole‐body crude protein and lipid content. ( p < 0.05). Serum analysis showed a significant reduction in total bilirubin (TBIL) and triglycerides (TG), and an increase in BA and lipoprotein cholesterol (LDL‐C) in the G3 group compared to G1 ( p < 0.05). The 0.10% BA supplementation downregulated pro‐inflammatory gene expression, like il-1β , and upregulated lipid metabolism‐related genes, like scdb , in the intestinal tract of O. mykiss ( p < 0.05). 16S high‐throughput sequencing identified key microbial groups in the intestine of O. mykiss , highlighting significant differences in microbial composition with BA supplementation. Metabolomic analysis revealed that BA addition altered the metabolic profile of O. mykiss , affecting pathways such as polycyclic aromatic hydrocarbon (PAH) catabolism, cysteine (Cys) and methionine (Met) metabolism, the sulfur relay system, arachidonic acid (AA) metabolism, and ovarian steroidogenesis. In summary, a 0.10% BA addition to the diet of O. mykiss significantly improved growth performance, mitigated intestinal inflammation in specimens fed low fishmeal diets, and promoted overall gut health and lipid metabolism.