Atlantic halibut

The Atlantic halibut is a right-eyed flounder. It is flattened sideways and habitually lies on the left side of its body with both eyes migrating to the right side of its head during development. When the larvae are born, they start in the upright position like most other fish having one eye on each side of the head. Once the larvae reach one inch in length, the left eye moves over the snout to the right side of the head. At the same time, the coloring on the left side begins to fade to white while the upper side of the fish is a uniformly dark chocolate, olive or slate color, and can be almost black. The end of the caudal fin is concave.[7] Young fish are paler with more mottled coloration.[8] Male adults average about 10 to 15 kilograms (25–30 lb) but can range to upwards of 25 kg (60 lb), rarely reaching 45 kg (100 lb). Females can get as large as 250 kg (600 lb).

Atlantic Halibut have a relatively slow growth rate and late onset of sexual maturity, with males attaining maturity at seven to eight years old, females at 10 to 11 years, and individuals averagely live around 25 to 30 years old. The oldest to have been caught was 50 years old. The Alaskan Halibut is a batch spawner where females lay anywhere from a few thousand to four million eggs (depending on the size and age of the fish, older females tend to lay only two million in one spawning period). Spawning occurs between December and April near the bottom of the ocean between 5 and 7 °C (41 and 45 °F). The egg size is around 3.0–3.8 mm and the larvae at time of hatching is 6.5 mm. Growth weight is dependent on the density, competition, and availability of food.

This marine fish usually lives on the ocean floor at depths between 50 and 2,000 m (200 and 6,600 ft), but it occasionally comes closer to the surface. The larvae are pelagic, drifting relatively helplessly, but at around 4 cm, they migrate to the bottom. Young between the ages of two and four years live close to the shore, moving into deeper waters as they grow older.[5][8]

Found in both the eastern and western portions of the North Atlantic. In the western Atlantic, found from southwestern Greenland and Labrador, Canada to Virginia in the USA. They are found in the eastern Atlantic around Iceland, the United Kingdom, Ireland and northern Europe to Russia. A map of the Atlantic Halibut's geographic distribution can be found on the Official Website of Massachusetts Division of Marine Fisheries.[9]

This demersal fish is found ranging from the latitude and longitude coordinates: 79°N - 36°N, 77°W - 55°E.

The Atlantic halibut occupies a relatively high trophic level in the food chain.

The diet of the Atlantic halibut consists mainly of other fish, e.g. cod, haddock, herring, pogge, sand eels and capelin, but it will also eat cephalopods, large crustaceans and other benthos organisms.[5][7]

During the first year of their life, halibut mostly feed on plankton. Once they turn 1, they feed on euphausiids and small fish until around age 3. As the halibut grows, the diet mostly consists of other fish including smaller halibut.

Atlantic halibut are eaten by seals, and are a staple food of the Greenland shark.[7] Killer whales are also natural predators of the halibut. Humans also consume halibut.

The wild Atlantic halibut was formerly a very important food fish, but because of its slow rate of population growth, it is unable to recover quickly from overfishing, and the fishery has largely collapsed. Consequently, wild fish labelled as "halibut" are usually one of the other large flatfishes, including Pacific halibut, Hippoglossus stenolepis.

The most popular way to catch the Alaskan halibut is to use circle hooks that are baited with herring or other similar fish, fished from the bottom with cannonball weights of up to 36 ounces on a slider.

The survival rate of caught and released halibut is 95 percent owing to the lack of having a swim bladder and not severely suffering from changes in water pressure (as long as the captured halibut is in excellent condition).

Because of 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.[10]

In 1996, the IUCN rated it as Endangered and placed it on its Red List.[3]

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 information is available to indicate a need to list the species under the U.S. Endangered Species Act (ESA).[11] The American Fisheries Society has classified the species as "Vulnerable". In 2010, Greenpeace International added the Atlantic halibut to its seafood red list of "fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries."[12]

The Atlantic halibut has been on the endangered species list since 1996 because of overfishing. It became commercially important during the 19th century because of the great demand for its meat and halibut being one of the largest flatfishes and essentially easy to capture.

This article incorporates text from the ARKive fact-file "Atlantic halibut" under the Creative Commons Attribution-ShareAlike 3.0 Unported License and the GFDL.

atlantic-halibut/hippoglossus-hippoglossus Atlantic halibut media from ARKive

• Video of larval Atlantic halibut reared in a tank and feeding on Artemia