Cod is the common name for the genus Gadus of demersal fishes, belonging to the family Gadidae. Cod is also used as part of the common name for a number of other fish species, and there are species suggested to belong to genus Gadus that are not called cod (the Alaska pollock).
The two most important species of cod are the Atlantic cod (Gadus morhua), which lives in the colder waters and deeper sea regions throughout the North Atlantic, and the Pacific cod (Gadus macrocephalus), found in both eastern and western regions of the northern Pacific. Gadus morhua was named by Linnaeus in 1758. (However, G. morhua callarias, a low salinity, non-migratory race restricted to parts of the Baltic, was originally described as Gadus callarias by Linnaeus.)
Cod is popular as a food with a mild flavour and a dense, flaky white flesh. Cod livers are processed to make cod liver oil, an important source of vitamin A, vitamin D, vitamin E and omega-3 fatty acids (EPA and DHA). Young Atlantic cod or haddock prepared in strips for cooking is called scrod. In the United Kingdom, Atlantic cod is one of the most common ingredients in fish and chips, along with haddock and plaice.
At various times in the past, taxonomists included many species in the genus Gadus. Most of these are now either classified in other genera, or have been recognized as simply forms of one of three species. All these species have a number of common names, most of them ending with the word "cod", whereas other species, as closely related, have other common names (such as pollock, haddock, etc.). On the other hand, many other, unrelated species also have common names ending with cod. The usage often changes with different localities and at different times.
Cod in the genus Gadus
There are three species in the Gadus genus currently called cod:
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|Cod in the genus Gadus:|
|Common name||Scientific name||Maximum
|Atlantic cod||Gadus morhua Linnaeus, 1758||200 cm||100 cm||96.0 kg||25 years||4.4||||||||Vulnerable|
|Pacific cod||Gadus macrocephalus Tilesius, 1810||119 cm||cm||22.7 kg||18 years||4.0||||||||Not assessed|
|Greenland cod||Gadus ogac Richardson, 1836||77.0 cm||cm||kg||12 years||3.6||||||||Not assessed|
Cod forms part of the common name of many other fish no longer classified in the genus Gadus. Many are members of the family Gadidae; others are members of three related families within the order Gadiformes whose names include the word "cod": the morid cods, Moridae (100 or so species); the eel cods, Muraenolepididae (four species); and the Eucla cod, Euclichthyidae (one species). The tadpole cod family (Ranicipitidae) has now been placed in Gadidae.
|Common name||Scientific name||Maximum
|Arctic cod||Arctogadus glacialis (Peters, 1872)||32.5 cm||cm||kg||years||3.8||||||Not assessed|
|East Siberian cod||Arctogadus borisovi Dryagin, 1932||55.6 cm||cm||1.5 kg||years||3.9||||||Not assessed|
|Eucla cod||Euclichthys polynemus McCulloch, 1926||35.0 cm||22.5 cm||kg||years||3.6||||||Not assessed|
|Common ling||Molva molva (Linnaeus, 1758)||200 cm||106 cm||45.0 kg||25 years||4.3||||||||Not assessed|
|Pelagic cod||Melanonus gracilis Günther, 1878||18.7 cm||cm||kg||years||3.5||||||Not assessed|
|Polar cod||Boreogadus saida (Lepechin, 1774)||40.0 cm||25.0 cm||kg||7 years||3.1||||||||Not assessed|
|Poor cod||Trisopterus minutus (Linnaeus, 1758)||40.0 cm||20.0 cm||kg||5 years||3.8||||||Not assessed|
|Rock cod||Lotella rhacina (Forster, 1801)||50.0 cm||cm||kg||years||3.5||||||Not assessed|
|Saffron cod||Eleginus gracilis (Tilesius, 1810)||55.0 cm||cm||1.3 kg||15 years||4.1||||||||Not assessed|
|Small-headed cod||Lepidion microcephalus Cowper, 1956||48.0 cm||cm||kg||years||3.5||||||Not assessed|
|Tadpole cod||Guttigadus globosus (Paulin, 1986)||18.1 cm||cm||kg||3.5 years||||||Not assessed|
Some fish commonly known as cod are unrelated to Gadus. Part of this name confusion is market-driven. Severely shrunken Atlantic cod stocks have led to the marketing of cod replacements using culinary names of the form "x cod", according to culinary rather than phyletic similarity. The common names for the following species have become well established; note that all inhabit the Southern Hemisphere.
- Blue cod Parapercis colias
- Eastern freshwater cod Maccullochella ikei
- Mary River cod Maccullochella peelii mariensis
- Murray cod Maccullochella peelii peelii
- Potato cod Epinephelus tukula
- Sleepy cod Oxyeleotris lineolatus
- Trout cod Maccullochella macquariensis
- The cod icefish family, Nototheniidae, including:
- Rock cod, reef cod, and coral cod
Almost all coral cod, reef cod or rock cod are also in order Perciformes. Most are better known as groupers, and belong to the family Serranidae. Others belong to the Nototheniidiae. Two exceptions are the Australasian red rock cod, which belongs to a different order (see below), and the fish known simply as the rock cod and as soft cod in New Zealand, Lotella rhacina, which as noted above actually is related to the true cod (it is a morid cod).
From the order Scorpaeniformes:
Marketed as cod
Some fish that do not have "cod" in their names are sometimes sold as cod. Haddock and whiting belong in the same family, the Gadidae, as cod.
Cods of the genus Gadus have three rounded dorsal and two anal fins. The pelvic fins are small, with the first ray extended, and are set under the gill cover (i.e. the throat region), in front of the pectoral fins. The upper jaw extends over the lower jaw, which has a well-developed chin barbel. The eyes are medium sized, approximately the same as the length of the chin barbel. Cod have a distinct white lateral line running from the gill slit above the pectoral fin, to the base of the caudal or tail fin. The back tends to be a greenish to sandy brown, and shows extensive mottling, especially towards the lighter sides and white belly. Dark brown colouration of the back and sides is not uncommon, especially for individuals that have resided in rocky inshore regions.
The Atlantic cod can change colour at certain water depths. It has two distinct colour phases: gray-green and reddish brown. Its average weight is 5–12 kilograms (11–26 lb), but specimens weighing up to 100 kilograms (220 lb) have been recorded. Pacific cod are smaller than Atlantic cod and are darker in colour.
Atlantic cod (Gadus morhua) live in the colder waters and deeper sea regions throughout the North Atlantic. Pacific cod (Gadus macrocephalus) is found in both eastern and western regions of the Pacific.
Atlantic cod divide into several stocks, including the Arcto-Norwegian, North Sea, Faroe, Iceland, East Greenland, West Greenland, Newfoundland, and Labrador stocks. There seems to be little interchange between the stocks, although migrations to their individual breeding grounds may involve distances of 200 miles (320 km)or more.
Atlantic cod occupy varied habitat, favouring rough ground, especially inshore, and are demersal in depths between 20 and 200 feet (6.1 and 61.0 m), 80 metres (260 ft) on average, although not uncommonly to depths of 600 metres (2,000 ft). Off the Norwegian and New England coasts and on the Grand Banks of Newfoundland, cod congregate at certain seasons in water of 30–70 metres (98–230 ft) depth. Cod are gregarious and form schools, although shoaling tends to be a feature of the spawning season.
Spawning of northeastern Atlantic cod occurs between January and April (March and April are the peak months), at a depth of 200 metres (660 ft) in specific spawning grounds at water temperatures between 4 and 6 °C (39 and 43 °F). Around the UK, the major spawning grounds are in the middle to southern North Sea, the start of the Bristol Channel (north of Newquay), the Irish Channel (both east and west of the Isle of Man), around Stornoway, and east of Helmsdale.
Prespawning courtship involves fin displays and male grunting, which leads to pairing. The male inverts himself beneath the female, and the pair swim in circles while spawning. The eggs are planktonic and hatch between eight and 23 days, with larva reaching 4 millimetres (0.16 in) in length. This planktonic phase lasts some ten weeks, enabling the young cod to increase its body weight by 40-fold, and growing to about 2 centimetres (0.79 in). The young cod then move to the seabed and change their diet to small benthic crustaceans, such as isopods and small crabs. They increase in size to 8 centimetres (3.1 in) in the first six months, 14–18 centimetres (5.5–7.1 in) by the end of their first year, and to 25–35 centimetres (9.8–13.8 in) by the end of the second. Growth tends to be less at higher latitudes. Cod reach maturity at about 50 centimetres (20 in) at about 3 to 4 years of age.
In the Baltic Sea the most important species[clarification needed] are Atlantic cod, herring, and sprat. Many studies that analyze the stomach contents of these fish indicate that cod is the top predator, preying on the herring and sprat. Sprat form particularly high concentrations in the Bornholm Basin in the southern Baltic Sea. Although cod feed primarily on adult sprat, sprat tend to prey on the cod eggs and larvae.
Cod and related species are plagued by parasites. For example the cod worm, Lernaeocera branchialis, starts life as a copepod, a small free-swimming crustacean larva. The first host used by cod worm is a flatfish or lumpsucker, which they capture with grasping hooks at the front of their body. They penetrate the lumpsucker with a thin filament which they use to suck its blood. The nourished cod worms then mate on the lumpsucker. The female worm, with her now fertilized eggs, then finds a cod, or a cod-like fish such as a haddock or whiting. There the worm clings to the gills while it metamorphoses into a plump, sinusoidal, wormlike body, with a coiled mass of egg strings at the rear. The front part of the worms body penetrates the body of the cod until it enters the rear bulb of the host's heart. There, firmly rooted in the cod's circulatory system, the front part of the parasite develops like the branches of a tree, reaching into the main artery. In this way, the worm extracts nutrients from the cod's blood, remaining safely tucked beneath the cod's gill cover until it releases a new generation of offspring into the water.
The 2006 northwest Atlantic cod quota is 23,000 tons, representing half the available stocks, while the northeast Atlantic quota is 473,000 tons. Pacific cod is currently enjoying strong global demand. The 2006 total allowable catch (TAC) for the Gulf of Alaska and Aleutian Islands was 260,000 tons.
Farming of Atlantic cod has received a significant amount of interest due to the overall trend of increasing cod prices alongside reducing wild catches. However, progress in creating large scale farming of cod has been slow, mainly due to bottlenecks in the larval production stage, where survival and growth are often unpredictable. It has been suggested that this bottleneck may be overcome by ensuring cod larvae are fed diets with similar nutritional content as the copepods they feed on in the wild  Recent examples have shown that increasing dietary levels of minerals such as selenium, iodine and zinc may improve survival and/or biomarkers for health in aquaculture reared cod larvae. 
Cod is popular as a food with a mild flavor and a dense, flaky white flesh. Cod livers are processed to make cod liver oil, an important source of vitamin A, vitamin D, vitamin E and omega-3 fatty acids (EPA and DHA).
Young Atlantic cod or haddock prepared in strips for cooking is called scrod. In the United Kingdom, Atlantic cod is one of the most common ingredients in fish and chips, along with haddock and plaice. Cod's soft liver can be tinned (canned) and eaten. It is an important source of vitamin A, vitamin D, vitamin E and omega-3 fatty acids (EPA and DHA). Cod is mainly consumed in Portugal, Spain, Italy and Brazil. Cod flesh is white, moist, and flaky when cooked.
Following the early 1990s collapse of Canadian stocks, the Canadian Department of Fisheries and Oceans (DFO) banned fishing for northern (that is, cod to the north and east of the island of Newfoundland, in NAFO areas JKL) cod in 1992, which caused great economic hardship in Newfoundland and Labrador. The collapse was blamed on cold water, or seals, and it had even been suggested the cod were really still there; only rarely was overfishing acknowledged, or management's role in that.
The DFO partly lifted its ban in 1997, although the International Council for the Exploration of the Sea noted the poor recovery of Canadian cod stocks. In general, depleted populations of cod and other gadids appear to recover poorly when fishing pressure is reduced or stopped.
In 1998, the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) listed the Atlantic cod as "vulnerable", a category subsequently rebranded as "special concern", though not as an endangered species. Dr. Kim Bell, who drafted the report for COSEWIC, subsequently stated the original report in fact had advised endangered status, but political pressure by the DFO within COSEWIC had resulted in a decision of vulnerable.
In 2000, WWF placed cod on the endangered species list. The WWF issued a report stating the global cod catch had suffered a 70% drop over the last 30 years, and if this trend continued, the world’s cod stocks would disappear in 15 years. Åsmund Bjordal, director of the Norwegian Institute of Marine Research disputed the WWF's claim, noting the healthy Barents Sea cod population. Cod is among Norway's most important fishery exports and the Barents Sea is Norway's most important cod fishery.
In 2003, under the new legislative framework of the Species At Risk Act [SARA], COSEWIC placed the Newfoundland and Labrador fisheries cod on the endangered species list and Fisheries Minister Robert Thibault announced an indefinite closure in the Gulf of St. Lawrence and off Newfoundland's northeast coast. In a 2004 report, the WWF agreed the Barents Sea cod fishery appeared to be healthy, but that the situation may not last due to illegal fishing, industrial development, and high quotas. In 2005, the WWF—Canada accused both foreign and Canadian fishing vessels of deliberate, large-scale violations of the restrictions on the Grand Banks, in the form of bycatch. WWF also claimed poor enforcement by NAFO, an intergovernmental organization with a mandate to provide scientific fishery advice and management in the northwestern Atlantic.
In 2006, the Norwegian Institute of Marine Research considered coastal cod (but not the North East Arctic cod) endangered, but has since reversed this assessment. In 2010, Greenpeace International added the Atlantic cod to its seafood red list. "The Greenpeace International seafood red list is a 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." According to Seafood Watch, cod is currently on the list of fish consumers should avoid. In the book The End of the Line, it is claimed cod is an example of how unsustainable fishing is destroying ocean ecosystems.
Cod has been an important economic commodity in international markets since the Viking period (around 800 AD). Norwegians traveled with dried cod and soon a dried cod market developed in southern Europe. This market has lasted for more than 1,000 years, enduring the Black Death, wars and other crises, and is still an important Norwegian fish trade. The Portuguese began fishing cod in the 15th century. Clipfish is widely enjoyed in Portugal. The Basques played an important role in the cod trade, and allegedly found the Canadian fishing banks before Columbus' discovery of America. The North American east coast developed in part due to the vast cod stocks. Many cities in the New England area are located near cod fishing grounds. The fish was so important to the history and development of Massachusetts, the state's House of Representatives hung a wood carving of a codfish, known as the Sacred Cod of Massachusetts, in its chambers.
Apart from the long history, cod differ from most fish because the fishing grounds are far from population centers. The large cod fisheries along the coast of North Norway (and in particular close to the Lofoten islands) have been developed almost uniquely for export, depending on sea transport of stockfish over large distances. Since the introduction of salt, dried and salted cod (clipfish or 'klippfisk' in Norwegian) has also been exported. By the end of the 14th century, the Hanseatic League dominated trade operations and sea transport, with Bergen as the most important port.
In the 17th and 18th centuries in the New World, especially in Massachusetts and Newfoundland, cod became a major commodity, creating trade networks and cross-cultural exchanges. In 1733, Britain tried to gain control over trade between New England and the British Caribbean by imposing the Molasses Act, which they believed would eliminate the trade by making it unprofitable. The cod trade grew instead, because the "French were eager to work with the New Englanders in a lucrative contraband arrangement". In addition to increasing trade, the New England settlers organized into a "codfish aristocracy". The colonists rose up against Britain's "tariff on an import".
In the 20th century, Iceland re-emerged as a fishing power and entered the Cod Wars. In the late 20th and early 21st centuries, fishing off the European and American coasts severely depleted stocks and become a major political issue. The necessity of restricting catches to allow stocks to recover upset the fishing industry and politicians reluctant to hurt employment.
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- fishbase.org – Scientific Names for Gadus
- Fisheries Heritage website, Newfoundland and Labrador
- Long term trends in Norwegian cod fisheries – the pioneers
- Species factsheet on cod from the UK Sea Fish Industry Authority (PDF, 2MB)