Roles of lipid-soluble vitamins during ontogeny of marine fish larvae

The roles of lipid-soluble vitamins during ontogeny of marine fish larvae are a subject topic where only fragments of the whole picture are known. Most of the research has been focussed on the larval requirements and the availability of these vitamins in the live feed organisms used for early-stage larvae, while the function of the vitamins in the larvae themselves is largely unknown. Our knowledge is mostly extrapolated from research on other vertebrates and also in part from juvenile and adult fish. Vitamin A is known to be essential for establishing body and organ axes in vertebrate embryos and interacts with other nutrients such as vitamin D and fatty acids through the steroid/thyroid nuclear hormone receptor family. In marine fish larvae, excess vitamin A stimulates pigmentation, but at the same time induces vertebral deformities. Live feed organisms contain very little vitamin A but marine fish larvae appear to convert carotenoids in Artemia and copepods to vitamin A, while rotifers, which contain little carotenoids, should be enriched with vitamin A. Vitamin E acts as an antioxidant and is important for the protection of marine fish larvae against the oxidation pressure probably present in intensive rearing systems. Vitamin E may also have other roles connected to its modulation of cell and tissue red-ox balance. In marine fish larvae and juveniles, vitamin E has been shown to enhance the symptoms of vitamin C deficiency, while protecting against the oxidative effect of n-3 fatty acids. Vitamin D is important for the modulation of calcium and phosphorus homeostasis and for the development of the vertebrate skeleton. Vitamin K influences bone development and coagulation of the blood. There is little information on vitamins D and K connected to the ontogeny of marine fish larvae.