Dietary bile acids supplementation on growth performance and metabolism in Pacific white shrimp (Litopenaeus vannamei)
Optimizing bile acids (BAs) inclusion in commercial diets and understanding its molecular mechanisms in Pacific white shrimp (Litopenaeus vannamei) are crucial for improving growth performance. The present study investigated the potential mechanism of how dietary BAs levels regulate Pacific white shrimp growth performance and metabolism using multi-omics approaches. A total of 1,800 shrimp (0.16 +/- 0.01 g) were randomly assigned to 36 tanks (50 shrimp per tank) and fed six diets with graded BAs levels: 0 mg kg-1 (control, BA0), 50 mg kg-1 (BA1), 100 mg kg-1 (BA2), 150 mg kg-1 (BA3), 200 mg kg-1 (BA4), and 250 mg kg-1 (BA5). Each diet was assigned randomly to six replicate tanks. Over a 56-day feeding trial, the results showed that the growth performance of BA4 and BA5 groups was significantly higher than that of BA0, BA1, and BA2 groups, with regression analysis estimating an optimal dietary BAs level range of 216-218 mg kg-1 diet. Biochemical analysis indicated that the dietary optimal BA supplementation group (BA4) significantly reduced Pacific white shrimp crude lipid content, hemolymph total triglycerides, and non-esterified fatty acids while increasing hepatopancreas trypsin activity, and hepatopancreatic and intestine lipase activity when compared with those in the BA0 group. Transcriptomic and metabolomic analyses from the BA4 group and the BA0 group were conducted. RNA-seq revealed reduced expression of lipid synthesis (elovl6, scd, agpat1, mogat1, acot1, acsl, fasn, plin3, srebp1, gstk1, and spla2) genes, whereas increased the expression of genes involved in lipid catabolism (acox1, angpt4, dip13a, and gba), bile acid secretion (slc5a1, abcg2, and ugt) and digestive enzymes (prss1 and prss2), indicating optimal BAs inclusion decreased lipid synthesis and improved nutrient acquisition. BAs-targeted metabolomic analysis indicated that taurine-conjugated BAs were predominant, and exogenous BAs supplementation did not significantly alter BAs pool composition. Untargeted metabolomics identified 22 upregulated and 15 downregulated metabolites. Notably, a significant decrease in taurine content was observed, likely due to the conjugation of BAs with taurine to form conjugated BAs, which are lost in this form via feces. In conclusion, the optimal inclusion of dietary BAs level was estimated to be 216-218 mg kg-1 of diet, with a fishmeal content constituting 220 g kg-1 of dry matter in Pacific white shrimp. This optimal level of BAs enhanced Pacific white shrimp growth and improved lipid metabolism by enhancing nutrient digestion, increasing digestive enzyme activity, promoting lipolysis, and inhibiting lipid synthesis without affecting the balance of BAs. Additionally, this study reported for the first time that taurine plays a critical role in Pacific white shrimp BAs metabolism.