Origin of tunaxanthin in the integument of yellowtail (Seriola quinqueradiata)

Abstract 1. 1. Bioconversion of astaxanthin and lutein was examined by feeding experiments of yellowtail. 2. 2. Carotenoid contents in the integuments of the fish fed the diets supplemented with astaxanthin or lutein were markedly increased. 3. 3. In every test fish, the same nine carotenoids, tunaxanthins C, B and A, 3′-epilutein, lutein, zeaxanthin, diatoxanthin, cynthiaxanthin and β-carotene triol were detected. 4. 4. Astaxanthin was presumably metabolized to tunaxanthins C or B, via β-carotene triol, zeaxanthin and 3′-epilutein. Lutein seemed to be metabolized to tunaxanthins C or B, via 3′-epilutein. 5. 5. Sources of tunaxanthin in the integuments of marine fish were estimated to be astaxanthin, lutein and probably zeaxanthin all of which are very common carotenoids in marine organisms.