cod omelette

Cod is the common name for the demersal fish genus '' Gadus'', belonging to the family Gadidae. Cod is also used as part of the common name for a number of other fish species, and one species that belongs to genus ''Gadus'' is commonly not called cod (Alaska pollock, ''Gadus chalcogrammus'').

The two most common species of cod are the Atlantic cod, 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, nonmigratory 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, a common 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, along with haddock and plaice.

Species

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 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 and haddock). However, 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''

Three species in the genus ''Gadus'' are currently called cod:

The fourth species of genus Gadus, '' Gadus chalcogrammus'', is commonly called ''Alaska pollock'' or ''walleye pollock''. But there are also less widespread alternative trade names highlighting the fish's belonging to the cod genus, like ''snow cod''SeafoodSource.com (23 January 2014):
Alaska pollock
''. or ''bigeye cod''.

Related species

''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.

Some fish have common names derived from "cod", such as codling, codlet, or tomcod. ("Codling" is also used as a name for a young cod.)

Other species

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.

Perciformes

Fish of the order Perciformes that are commonly called "cod" include:
* 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 notothen family, Nototheniidae, including:
** Antarctic cod ''Dissostichus mawsoni''
** Black cod ''Notothenia microlepidota''
** Maori cod ''Paranotothenia magellanica''

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 Nototheniidae. 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).

Scorpaeniformes

From the order Scorpaeniformes:
* Ling cod ''Ophiodon elongatus''
* Red rock cod ''Scorpaena papillosa''
*Rock cod ''Sebastes''

Ophidiiformes

The tadpole cod family, Ranicipitidae, and the Eucla cod family, Euclichthyidae, were formerly classified in the order Ophidiiformes, but are now grouped with the Gadiformes.

Marketed as cod

Some fish that do not have "cod" in their names are sometimes sold as cod. Haddock and whiting belong to the same family, the Gadidae, as cod.
* Haddock ''Melanogrammus aeglefinus''
* Whiting ''Merlangius merlangus''
* Patagonian toothfish or Chilean seabass

Characteristics

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."Cod"
, ''Encyclopædia Britannica online'' 2008

Atlantic cod divide into several stocks, including the Arcto-Norwegian, North Sea, Baltic 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 or more. For instance, eastern Baltic cod shows specific reproductive adaptations to low salinity compared to Western Baltic and Atlantic cod.

Atlantic cod occupy varied habitat, favouring rough ground, especially inshore, and are demersal in depths between , on average, although not uncommonly to depths of . Off the Norwegian and New England coasts and on the Grand Banks of Newfoundland, cod congregate at certain seasons in water of depth. Cod are gregarious and form schools, although shoaling tends to be a feature of the spawning season.

Life cycle

Spawning of northeastern Atlantic cod occurs between January and April (March and April are the peak months), at a depth of in specific spawning grounds at water temperatures between . 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 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 . 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 in the first six months, by the end of their first year, and to by the end of the second. Growth tends to be less at higher latitudes. Cod reach maturity at about at about 3 to 4 years of age. Changes in growth rate over decades of particular stocks have been reported, current eastern Baltic cod shows the lowest growth observed since 1955.

Ecology

Adult cod are active hunters, feeding on sand eels, whiting, haddock, small cod, squid, crabs, lobsters, mussels, worms, mackerel, and molluscs.

In the Baltic Sea the most important prey species are herring