Exogenous bile acids regulate energy metabolism and improve the health condition of farmed fish

The rapid expansion of aquaculture has led to increased demand for protein sources for feed production. Lipids and carbohydrates can serve as energy sources and induce a “protein-sparing” effect. However, excessive dietary lipids and carbohydrates may cause lipid accumulation in the liver, impair immune and antioxidant capacities, thus hidering the growth and meat quality of farmed fish. Bile acids are physiological detergents that are initially synthesized in the liver. They can not only accelerate absorption and transportation of lipid and lipid-soluble nutrients, but also regulate energy metabolism and health condition as molecular signals. Recent studies revealed that exogenous bile acids can maintain lipid and glucose homeostasis, improve fish health and growth performance hampered by high lipid or high carbohydrate diet. However, such beneficial effects are limited and vary with fish species. The mechanisms and theories behind the different results should be elucidated. Thus, this review aims to summarize the biosynthesis, metabolism, and circulation of bile acids, the mechanisms of exogenous bile acids on growth promotion, lipid and glucose homeostasis, antioxidant and immune capacities, as well as the crosstalk between bile acids and intestinal microbiota. This paper will provide a clear view of the mechanisms, prospects, and potential risks of using bile acids as feed additives in fish, which may benefit their further application in the aquatic feed industry.