Metabolism of cryptoxanthin in freshwater fish

In search of other provitamins A, the metabolism of cryptoxanthin was studied in several species of freshwater fish, i.e. Channa gachua, Labeo boga (retinol-rich) and Heteropneustes fossilis (dehydroretinol-rich). The fish were either allowed to starve for 20-25 d to make their intestines free from carotenoids and vitamin A or kept on a vitamin-A-deficient diet for 140-150 d to deplete the initial reserve of vitamin A in the livers. Retinol-rich freshwater fish such as C. gachua and L. boga converted cryptoxanthin into retinol and no 3-dehydroretinol or 3-hydroxyretinol could be isolated from those fish that received cryptoxanthin. 3-Hydroxyretinol and 3-dehydroretinol were isolated from the vitamin-A-deficient H. fossilis, a 3-dehydroretinol-rich freshwater siluroid, after the administration of cryptoxanthin.