Canthaxanthin, also known as Cantaxanthin, Cantaxanthine, or Canthaxanthine is a keto-carotenoid, a pigment widely distributed in nature. Carotenoids belong to a larger class of phytochemicals known as terpenoids. Canthaxanin is also classified as a xanthophyll. Xanthophylls are yellow pigments and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes. Both are carotenoids. Xanthophylls and carotenes are similar in structure, but xanthophylls contain oxygen atoms while carotenes are purely hydrocarbons, which do not contain oxygen. Their content of oxygen causes xanthophylls to be more polar (in molecular structure) than carotenes and causes their separation from carotenes in many types of chromatography. (Carotenes are usually more orange in color than xanthophylls. Canthaxanthin is naturally found in bacteria, algae and some fungi. Canthaxanthin is associated with E number E161g and is approved for use as a food coloring agent in different countries, including the United States and the EU. Canthaxanthin is used as poultry feed additive to yield red color in skin and yolks. The European Union permits the use of canthaxanthin in feedstuff at a maximum content of 25 mg/kg of final feedstuff while the United States allows the use of this pigment in broiler chicken and salmonid fish feeds. Canthoxanthin was first isolated in edible chanterelle mushroom (Cantharellus cinnabarinus), from which it derived its name. It has also been found in green algae, bacteria, archea (a halophilic archaeon called Haloferax alexandrines), fungi and bioaccumulates in tissues and egg yolk from wild birds and at low levels in crustaceans and fish such as carp, golden grey mullet, and seabream. Canthaxanthin is not found in wild Atlantic Salmon, but is a minor carotenoid in Pacific Salmon. Canthaxanthin is used in farm-raised trout to give a red/orange color to their flesh similar to wild trout. Canthaxanthin has been used as a food additive for egg yolk, in cosmetics and as a pigmenting agent for human skin applications. It has also been used as a feed additive in fish and crustacean farms. Canthaxanthin is a potent lipid-soluble antioxidant (PMID: 2505240). Canthaxanthin increases resistance to lipid peroxidation primarily by enhancing membrane alpha-tocopherol levels and secondarily by providing weak direct antioxidant activity. Canthaxanthin biosynthesis in bacteria and algae proceeds from beta-carotene via the action of an enzyme known as a beta-carotene ketolase, that is able to add a carbonyl group to carbon 4 and 4' of the beta carotene molecule.