The distribution of vitamins A(1) and A(2) has been determined in the eye tissues and livers of a number of fishes. The vitamins were differentiated by means of the antimony chloride reaction, which yields with A(1) a band at 615-620 mmicro and with A(2) a band at about 696 mmicro. In the retina the presence of vitamin A(1) is diagnostic of the operation of a rhodopsin, and vitamin A(2) of a porphyropsin cycle. The eye tissues of all permanently marine fishes examined, except the tautog, contain vitamin A(1) alone. Those of all permanently freshwater fishes possess only vitamin A(2). Those of all euryhaline (potentially migratory) fishes, except possibly the alewife, contain mixtures of both vitamins A, and always predominantly that one which ordinarily is associated with the environment in which the fish is spawned. These correlations extend in part to the liver oils, but most livers contain mixtures of both vitamins A, and occasionally in proportions the reverse of those in the eye tissues. The vitamin A configuration does not depend upon environmental circumstances, but is determined genetically. The transfer from vitamin A(1) to A(2) metabolism appears associated phylogenetically with migration of marine teleosts into fresh water.