Insulin is a member of a family of peptides and plays important roles in the regulation of nutrition metabolism in fish. To decipher the mechanism of insulin regulating nutrient metabolism, the present paper reviewed the progress involved in the structure and expression of three members (insulin, insulin receptor and insulin receptor substrate) of insulin signaling pathways, and the regulation of insulin in carbohydrate, lipid and protein metabolism. At present, although enormous progress has been made in the insulin signaling pathway, many basic questions remain and further investigations are needed: (1) studies involved in the functions of different isoforms of insulin, insulin receptor and insulin receptor substrate; (2) molecular mechanism of insulin regulating nutrient metabolism; (3) investigation into insulin signaling pathway and regulatory mechanism.