Involved in the biosynthesis of ketocarotenoids which are powerful anti-oxidative molecules (PubMed:21398427, PubMed:22526507). Catalyzes the conversion of zeaxanthin to astaxanthin via adonixanthin (PubMed:21398427, PubMed:22526507). Catalyzes the conversion of beta-carotene to canthaxanthin via echinenone (PubMed:21398427, PubMed:22526507). 2 AH2 + all-trans-adonixanthin + 2 O2 = 2 A + all-trans-(3S,3'S)-astaxanthin + 3 H2O 2 AH2 + all-trans-zeaxanthin + 2 O2 = 2 A + all-trans-adonixanthin + 3 H2O 2 AH2 + echinenone + 2 O2 = 2 A + canthaxanthin + 3 H2O 2 AH2 + all-trans-beta-carotene + 2 O2 = 2 A + echinenone + 3 H2O Carotenoid biosynthesis; astaxanthin biosynthesis.