All vertebrates, including fishes, absorb vitamin D directly from their diet (Dussoet al. 2005). Dietary fat and fat-soluble vitamins are absorbed and transported in chylomicrons, the major lipoproteins synthesized by the intestine, via the blood to the liver (Haddad et al. 1993). Mammals synthesize previtamin D in their skin from a photochemical precursor, 7-dehydrocholesterol (7-DHC), formed from cholesterol by ultraviolet (UV) light irradiation (Holick et al. 1977, 1980; Holick 1981). The previtamin D is later transformed into vitamin D by thermal isomerization (Okano et al. 1977) and transported, bound to vitamin D binding protein (DBP), via the blood to the liver (Haddad et al. 1993).