Carbohydrates are cheaper ingredients source to satiate the energy requireme nts of fish. Fish oil is a limited resource that needs to be reduced or replaced in fish feeds by using sustainable alternatives. Therefore, the goal of this study was to improve the carbohydrate (CHO) utilization by reducing lipid inclusion in the diets and assessing whether dietary bile acid (BA) supplementation enhanced lipid utilization. Hence, three variables such lipid and CHO inclusion level and bile acid supplementation, led to a 2 × 2 × 2 factorial experimental design. Largemouth bass juveniles (average weight: 6.0 g) were fed (8 isonitrogenous diets: 45% crude protein) different combinations of dietary high (HF: 12%) and low fat (LF: 9%) and high (HS: 30%) and low starch (LS: 20% ) levels with or without bile acid (BA) supplementations at 1% for 8 weeks.
Growth performance of fish was significantly affected by dietary treatments. The weight gain of individual fish was highest in the LF/HS-BA treatment, which was significantly higher than the other diets with BA supplementations. In terms of gut microbiome results, alpha diversity was significantly unaffected by different level of fat and carbohydrate among the treatments, however a significant increase was observed by the addition of bile in the HF-LS diet. Moreover, linear mixed effects model analysis revealed significant effects coming from the starch levels on the richness of the gut communities (P=0.02), indicating decreasing richness with increasing starch levels (Figure 1A). Looking at the beta-diversity (microbial composition), the microbial communities were affected by both the bile addition (P=0.036) and the interaction between fat, starch and bile addition (P=0.01), as indicated by Permanova and Principal Coordinate analysis (Figure 1B) . Among the genera, Clostridium was the most abundant taxon, followed by Lactobacillus, Paraclostridium , Plesiomonas , Candidatus Arthromitus , Cetobacterium and Lactococcus . Data for distal intestinal morphology will be presented.
Conclusively, dietary supplementation of bile acid in high dietary carbohydrate fed group can improve the growth performance and gut health via maintaining the gut microbial community.