Physiological function of vitamin D₃ in fish

Abstract Vitamin D (VD) is a steroid hormone, of which vitamin D 3 (VD 3 ) is the main form in fish. Fish obtain VD 3 majorly from diets, and VD 3 has been widely used in aquatic feed as feed additive. As one of the essential nutrients, VD 3 plays an indispensable role in the growth and health of fish. Due to the particularity of the fish living environment, the metabolic and physiological functions of VD 3 in fish have some differences from those of mammals. This paper reviews the metabolic process of VD 3 in fish, the main metabolites and vitamin D receptors, compares the differences in VD 3 metabolism between fish and mammals, summarises the recommended dietary requirements for VD 3 in several fish species, generalises the role of VD 3 in fish growth performance, bone development, lipid metabolism, immune regulation, antioxidant and other potential physiological functions, as well as its synergistic effects with other nutrients. Future perspectives of VD 3 application in aquaculture are proposed. Understanding the metabolic process and physiological function of VD 3 is of great significance for extending VD 3 application in the aquatic feed industry.