Halibut is the common name for three species of flatfish in the family of right-eye flounders. In some regions, and less commonly, other species of large flatfish are also referred to as halibut. The word is derived from haly (holy) and butte (flat fish), for its popularity on Catholic holy days. Halibut are demersal fish and are highly regarded as a food fish as well as a sport fish.
Species A 2018 cladistic analysis based on genetics and morphology showed that the Greenland halibut diverged from a lineage that gave rise to the Atlantic and Pacific halibuts. The common ancestor of all three diverged from a lineage that gave rise to the genus Verasper, comprising the spotted halibut and barfin flounder.
Genus Hippoglossus Atlantic halibut, Hippoglossus hippoglossus – lives in the North Atlantic Pacific halibut, Hippoglossus stenolepis – lives in the North Pacific Ocean Genus Reinhardtius Greenland halibut, Reinhardtius hippoglossoides – lives in the cold northern Atlantic, northern Pacific, and Arctic Oceans
Physical characteristics The Pacific and Atlantic halibut are the world's largest flatfish, with debate over which grows larger. Halibut are dark brown on the top side with a white to off-white underbelly and have very small scales invisible to the naked eye embedded in their skin. Halibut are symmetrical at birth with one eye on each side of the head. Then, about six months later, during larval metamorphosis one eye migrates to the other side of the head. The eyes are permanently set once the skull is fully ossified. At the same time, the stationary-eyed side darkens to match the top side, while the other side remains white. This color scheme disguises halibut from above (blending with the ocean floor) and from below (blending into the light from the sky) and is known as countershading. The IGFA size record for halibut was apparently broken off the waters of Norway in July 2013 by a 234-kilogram (515-pound), 2.62-metre (8-foot-7-inch) fish. This was awaiting certification as of 2013. In July 2014, a 219-kilogram (482 lb) Pacific halibut was caught in Glacier Bay, Alaska; this is, however, discounted from records because the halibut was shot and harpooned before being hauled aboard.
Diet Halibut feed on almost any fish or animal they can fit into their mouths. Juvenile halibut feed on small crustaceans and other bottom-dwelling organisms. Animals found in their stomachs include sand lance, octopus, crab, salmon, hermit crabs, lamprey, sculpin, cod, pollock, herring, and flounder, as well as other halibut. Halibut live at depths ranging from a few meters to hundreds of meters, and although they spend most of their time near the bottom, halibut may move up in the water column to feed. In most ecosystems, the halibut is near the top of the marine food chain. In the North Pacific, common predators are sea lions, killer whales, salmon sharks and humans.
Sex-determining genes Halibut species vary in sex determination systems. The Atlantic halibut went down a purely XX/XY route, with the male being heterogametic, around 0.9 to 3.8 million years ago. The sex-determining gene for the Atlantic halibut is likely to be gsdf on chromosome 13. The Pacific halibut went down a ZZ/ZW route, with the female being heterogametic, around 4.5 million years ago. The master sex-determining gene of the Pacific halibut is located on chromosome 9 and it is likely to be bmpr1ba. The gene sox2 is likely to play the same role in the Greenland halibut.
Halibut fishery The North Pacific commercial halibut fishery dates to the late 19th century and today is one of the region's largest and most lucrative. In Canadian and US waters, long-line fishing predominates, using chunks of octopus ("devilfish") or other bait on circle hooks attached at regular intervals to a weighted line that can extend for several miles across the bottom. The fishing vessel retrieves the line after several hours to a day. The effects of long-line gear on habitats are poorly understood, but could include disturbance of sediments, benthic structures, and other structures. International management is thought to be necessary, because the species occupies waters of the United States, Canada, Russia, and possibly Japan (where the species is known to the Japanese as ohyo), and matures slowly. Halibut do not reproduce until age eight, when about 80 cm (30 in) long, so commercial capture below this length prevents breeding and is against US and Canadian regulations supporting sustainability. Pacific halibut fishing is managed by the International Pacific Halibut Commission. For most of the modern era, halibut fishery operated as a derby. Regulators declared time slots when fishing was open (typically 24–48 hours at a time) and fishermen raced to catch as many pounds as they could within that interval. This approach accommodated unlimited participation in the fishery while allowing regulators to control the quantity of fish caught annually by controlling the number and timing of openings. The approach led to unsafe fishing, as openings were necessarily set before the weather was known, forcing fishermen to leave port regardless of the weather. The approach limited fresh halibut to the markets to several weeks per year when the gluts would push down the price received by fishermen.
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