Interactive effects of dietary cholesterol and bile acids on the growth, lipid metabolism, immune response and intestinal microbiota of Litopenaeus vannamei: Sparing effect of bile acids on cholesterol in shrimp diets

Cholesterol (CHO) is an expensive essential nutrient for shrimp and bile acids (BA) are emulsifiers responsible for lipid absorption in vertebrates. This study was carried out to investigate the interactive effects of dietary CHO and BA on the growth performance, lipid metabolism, immune response and intestinal microbiota of Litopenaeus vannamei and explore the sparing effect of BA on CHO in shrimp diets. Shrimp with average initial weight of 1.27 +/- 0.18 g were fed with diets containing three levels of CHO (0.15, 0.2 and 0.3% of diet) with three levels of bile acid (0, 0.02 and 0.03% of diet, as a 3 x 3 experimental design) for 56 days. The growth performance of L. vannamei increased significantly (P < 0.05) with increasing dietary CHO and BA levels, and BA could exert CHOsparing effects in shrimp diets. Both dietary CHO and BA significantly affected serum biochemical indexes (total cholesterol, triglyceride, high-density lipoprotein cholesterol and low-density lipoprotein cholesterol) and increased hepatopancreatic protease and lipase activities in L. vannamei (P < 0.05). The interaction between dietary CHO and BA was observed for lipase activity in hepatopancreas as well as high-density lipoprotein cholesterol and low-density lipoprotein cholesterol contents in serum (P < 0.05). Only BA supplementation significantly enhanced the antioxidant capacity (total antioxidant capacity, superoxide dismutase activity and glutathione content) of hepatopancreas in L. vannamei (P < 0.05). The immune assay showed that at each CHO level, dietary 0.3% BA could promote antibacterial activity in plasma and the expression of immune-related genes (Imd and Relish) in intestine compared with L. vannamei without BA supplementation. High-throughput sequencing analysis revealed that the bacterial diversity and richness, the abundances of Bacteroidetes and functional genes associated with lipid metabolism all increased with increasing dietary CHO and BA levels.