Effects of BBR on growth performance, serum and hepatic biochemistry parameters, hepatic morphology and gene expression levels related to glucose metabolism in largemouth bass, Micropterus salmoides

Abstract

An 8-week experiment was performed to investigate the effects of BBR on growth performance, hepatic glucose metabolism, antioxidant capacity, liver histology and intestinal digestive enzyme activity of largemouth bass. Fish (initial weight ≈122 g) were randomly allocated into 16 cages (280 L, 30 fish per tank) and fed four isonitrogenous and isolipidic diets containing 0, 0.5, 1 and 2 g/kg BBR respectively. The results indicated that diets with 1 and 2 g/kg BBR significantly promoted growth, decreased serum glucose, triglycerides (TG), total cholesterol (TC) and low-density lipoprotein cholesterol but increased serum high-density lipoprotein cholesterol (p < 0.05). The application of BBR significantly decreased hepatic alanine aminotransferase, TG and TC but increased hepatic superoxide dismutase and catalase (p < 0.05). Diets with 1 and 2 g/kg BBR significantly decreased hepatic malondialdehyde, aspartate aminotransferase and hepatic glycogen but increased intestinal farnesoid X receptor and fibroblast growth factor-19 expression and dramatically altered its downstream glycolysis- and gluconeogenesis-related genes, along with their enzyme activities (p < 0.05). Supplementation with BBR increased (p < 0.05) intestinal protease activity in B5, B10 and B20, lipase activity in B10 and B20 and amylase activity in B20. BBR reduced the liver voiding rate and fat content. These results indicated that dietary supplementation with BBR at 1 and 2 g/kg was beneficial for promoting growth and health in largemouth bass. The improved glycolysis and inhibited gluconeogenesis may account for the reduced hyperglycaemia by BBR. In addition, enhancing the activity of intestinal digestive enzymes is an effective way for BBR to improve carbohydrate utilization in largemouth bass.