The retinae of rainbow trout, Salmo gairdneri, have mixtures of two visual pigments, one based on retinaldehyde (VP5031), the other on 3-dehydroretinaldehyde (VP5272). Increases in the proportion of VP5272 or maintained high percentages of VP5272 were induced in three ways: (1) feeding a diet rich in 3-dehydroretinol; (2) intraperitoneal injections of L-thyroxine; and (3) intramuscular injection of bovine thyrotropic hormone. The possible significance of these findings in relation to carotenoid conversions in fish is discussed.
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Jacquest et al. (1972) studied this question.