Metabolism of carotenoids in salmonids—I. idoxanthin, a metabolite of astaxanthin in the flesh of atlantic salmon (Salmon salar, L.) under varying external conditions

Abstract

Abstract 1. 1. Idoxanthin (3,3′,4′-trihydroxy-β,β-caroten-4-one) was found to be a metabolite of astaxanthin (3,3′-di-hydorxy-β,β-carotene-4,4′-dione) in Atlantic salmon. Idoxanthin was characterized by TLC, HPLC, VIS 1 H-NMR and MS. 2. 2. In experimental fish reared indoors in tanks, an increased formation and deposition of this metabolite in flesh was noticed, presumably as a result of stress. 3. 3. In farmed salmon kept in net cages in the open sea, idoxanthin was also found after one year of pigmentation, but had disappeared completely after two years when the fish had reached market size. 4. 4. Only minute amounts of idoxanthin were found in the flesh of wild Atlantic salmon comparable weights. 5. 5. Cofigurational and biochemical aspects of idoxanthin formation are discussed.