Effects of dietary primary bile acids on the growth, intestinal morphology, gene expression, serum metabolites and intestinal microbiota in pearl gentian grouper fed a high lipid diet

Abstract

The grouper aquaculture industry flavors high lipid diets for economic reasons, yet this inevitably produces negative effects on the growth performance and intestinal function. Bile acids have been extensively reported to mitigate the negative effects on fish fed a high lipid diet, but it remains unclear whether this mechanism is bile acid type dependent. Therefore, an eight-week feeding trial was conducted to investigate the response of growth and intestinal health parameters in pearl gentian grouper Epinephelus fuscoguttatus♂ × E. lanceolatus♀ fed with high lipid diets to different types of bile acids. A high lipid diet (diet HL) containing 167 g/kg crude lipid served as the control diet, and three of primary bile acids glycocholic acid, taurocholic acid, and cholic acid were added at a dose of 900 mg/kg to generate the bile acid diets HBG, HBT, and HBC, respectively. Results revealed that dietary supplementation with glycocholic acid, taurocholic acid, or cholic acid does not affect the feed intake and growth of pearl gentian grouper fed a high lipid diet, while increasing the relative abundance of intestinal opportunistic pathogens such as Staphylococcus and Pseudomonas in this species. Dietary supplementation with glycocholic acid or cholic acid decreases muscle layer thickness and villus height, while increases intestinal injury score. Grouper fed with taurocholic acid showed higher villus width and serum antioxidant enzyme activity, along with lower intestinal injury score and serum lipid peroxidation level. For the protein and gene involved in the PI3K/AKT/mTOR pathways, S6K1 signaling, and bile acids metabolism, grouper fed with taurocholic acid exhibited an increase in the protein expression of PP70 and the mRNA expression of nrf2, pi3k, pdk1, tsc2, akt, mtorc1, fxr and tgr5. Moreover, the serum metabolites can be significantly influenced by the intestinal bacteria. Overall, dietary supplementation of 900 mg/kg taurocholic acid is recommended when feeding high lipid diets to grouper.