Atlantic halibut large flatfishes, including Pacific halibut, "Hippoglossus stenolepis". Due to its popularity as a food fish, Atlantic halibut has attracted investment in fish farming. As of 2006, five countries - Canada, Norway, the UK, Iceland and Chile - were engaged in some form of Atlantic halibut aquaculture production. In 1996, the IUCN rated it as Endangered and placed it on its Red List. The Atlantic halibut is a US National Marine Fisheries Service Species of Concern, one of those species about which the U.S. Government's National Oceanic and Atmospheric Administration has some concerns regarding status and threats, but for which insufficient
Fish anatomy Their retinas generally have both rod cells and cone cells (for scotopic and photopic vision), and most species have colour vision. Some fish can see ultraviolet and some can see polarized light. Amongst jawless fish, the lamprey has well-developed eyes, while the hagfish has only primitive eyespots. The ancestors of modern hagfish, thought to be the protovertebrate were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one. Unlike humans, fish normally adjust focus by