Vitamin A occurs in two forms, vitamin A1 (retinol) found in mammals and marine fish, and vitamin A2 (retinol2), found in freshwater fish. Vitamin A is required in vertebrates for regeneration of light-sensitive compound rhodopsin in the retina. Vitamin A is also involved in calcium transport across some membranes, in reproduction and embryonic development, and in cellular and subcellular membrane integrity. Deficiency symptoms could be related to depigmentation and soft exoskeleton. Sources of vitamin A include fish liver oils and liver meals. Recommended supplementation level of vitamin A in commercial feeds is 10,000 IU/kg (Akiyama et al., 1992).