Abstract: Bile acids (BAs) constitute a class of amphipathic sterol compounds, categorized into primary and secondary bile acids based on their origins. Primary bile acids are synthesized from cholesterol in the liver and subsequently enter the intestine. In the intestine, primary bile acids undergo conversion into secondary bile acids by the intestinal flora, primarily in the terminal ileum and upper colon. The majority of bile acids in the intestine are returned to the liver through enterohepatic circulation in the ileum, while the remaining bile acids are excreted with feces. Research shows the significant role of bile acids in maintaining glycolipid homeostasis, improving immune function, and reshaping intestinal flora in fish. However, the composition, classification, and functions of bile acids in different fish species remain poorly understood. This article provides a comprehensive summary of bile acid composition, classification, main receptors, biological functions, and the current state of research and challenges in understanding bile acids in fish. The aim is to offer insights for further investigation into fish bile acids and their efficient utilization in aquaculture practices.