Enhancing Hepatic Antioxidant Capacity and Carbohydrate, Lipid, and Bile Acid Metabolism in Largemouth Bass Through Dietary Betaine Supplementation

This study aimed to investigate the effect of dietary betaine on the growth, glucose and lipid metabolism, and bile acid (BA) metabolism in Micropterus salmoides fed high-cottonseed concentrated protein (CPC) diets. In this study, Micropterus salmoides were fed six experimental diets: the basal diet (BD diet; high fish meal), the low-fish meal diet (LF diet; 75% of the fish meal protein in the BD diet was substituted with CPC), and four betaine-supplemented diets (1.0 g/kg, 2.0 g/kg, 4.0 g/kg, and 8.0 g/kg of betaine were added to the LF diet, designated as LFB1.0, LFB2.0, LFB4.0, and LFB8.0, respectively). After an 8-week feeding trial, compared with the BD diet, fish fed the LF diet had decreased weight gain rate, reduced feed utilization efficiency, and poor liver health and impaired metabolic function. Conversely, fish fed the LFB4.0 diet showed an increased weight gain rate and feeding rate, improved liver antioxidant capacity, and decreased hepatic lipid droplets and glycogen content. Non-targeted metabolomics of the liver revealed that betaine regulated carbohydrate and lipid metabolism and was associated with primary bile acid metabolism. Moreover, the hepatic levels of the BA regulatory factors short heterodimer partner and farnesoid-X-receptor, as well as the gene expression of BA transporter bile salt export pump, were increased in fish fed the LFB4.0 diet. Supplementing the LF diet (high CPC levels) with 4.0 g/kg betaine improves fish growth performance and enhances hepatic carbohydrate and lipid metabolism via the positive regulation of BA metabolism by betaine.