Metabolism of Carotenoids in Salmonids. Part 3. Metabolites of astaxanthin and canthaxanthin in the skin of atlantic salmon (salmo salar, L.)

Abstract Diets supplemented with astaxanthin and canthaxanthin, respectively, and a control diet without carotenoid additions, were fed to 1½‐year‐old Atlantic salmon ( Salmo salar , L.) for one year. The integuments were investigated as to their quantitative and qualitative carotenoid composition. Astaxanthin and canthaxanthin deposited in the skin amounted to 20 and 14% of the total carotenoids only. Seventy % must be considered as metabolites of astaxanthin and canthaxanthin and 10% as basic xanthophylls also present in the control groups. Astaxanthin apparently underwent the following metabolic pathway: astaxanthin→idoxanthin→adonixanthin→zeaxanthin→zeaxanthin 5,6‐epoxides. Reduction of the 4′‐carbonyl group was stereospecific leading to the (4′ R )‐idoxanthin. Canthaxanthin was obviously converted to β,β‐carotene via 4′‐hydroxyechinenone, echinenone, and 4‐hydroxy‐β,β‐carotene.