Astaxanthin is a carotenone that consists of beta,beta-carotene-4,4'-dione bearing two hydroxy substituents at positions 3 and 3' (the 3S,3'S diastereomer). A carotenoid pigment found mainly in animals (crustaceans, echinoderms) but also occurring in plants. It can occur free (as a red pigment), as an ester, or as a blue, brown or green chromoprotein. It has a role as an anticoagulant, an antioxidant, a food colouring, a plant metabolite and an animal metabolite. It is a carotenone and a carotenol. It derives from a hydride of a beta-carotene.