Cod

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 not commonly called cod.
The two most common species of cod are the Atlantic cod, which lives in the colder waters and deeper sea regions throughout the North Atlantic, and the Pacific cod, which is found in both eastern and western regions of the northern Pacific. Gadus morhua was named by Linnaeus in 1758.
Cod as food is popular in several parts of the world. It has 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. Scrod is young Atlantic cod or haddock. In the United Kingdom, Atlantic cod is one of the most common ingredients in fish and chips, along with haddock and plaice.

Species

At lots of 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. 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''/True cod

Three species in the genus Gadus are currently called cod:

Common name	Scientific name	Maximum length	Common length	Maximum weight	Maximum age	Trophic level	Fish Base	FAO	ITIS	IUCN status
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

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 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 ; the eel cods, Muraenolepididae ; and the Eucla cod, Euclichthyidae. The tadpole cod family has now been placed in Gadidae.

Common name	Scientific name	Maximum length	Common length	Maximum weight	Maximum age	Trophic level	Fish Base	FAO	ITIS	IUCN status
Arctic cod	Arctogadus glacialis	32.5 cm	cm	kg	years	3.8				Not assessed
East Siberian cod	Arctogadus borisovi	55.6 cm	cm	1.5 kg	years	3.9				Not assessed
Eucla cod	Euclichthys polynemus	35.0 cm	22.5 cm	kg	years	3.6				Not assessed
Common ling	Molva molva	200 cm	106 cm	45.0 kg	25 years	4.3				Not assessed
Pelagic cod	Melanonus gracilis	18.7 cm	cm	kg	years	3.5				Not assessed
Polar cod	Boreogadus saida	40.0 cm	25.0 cm	kg	7 years	3.1				Not assessed
Poor cod	Trisopterus minutus	40.0 cm	20.0 cm	kg	5 years	3.8				Not assessed
Rock cod	Lotella rhacina	50.0 cm	cm	kg	years	3.5				Not assessed
Saffron cod	Eleginus gracilis	55.0 cm	cm	1.3 kg	15 years	4.1				Not assessed
Small-headed cod	Lepidion microcephalus	48.0 cm	cm	kg	years	3.5				Not assessed
Tadpole cod	Guttigadus globosus	18.1 cm	cm	kg	3.5 years					Not assessed

Some fish have common names derived from "cod", such as codling, codlet, or tomcod.

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 mariensis
Murray cod Maccullochella peelii
Potato cod Epinephelus tukula
Sleepy cod Oxyeleotris lineolatus
Trout cod Maccullochella macquariensis
The notothen family, Nototheniidae, including:
*Antarctic cod Dissostichus mawsoni
**Dissostichus eliginoides, the Patagonian toothfish, is also marketed as "cod"
*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, 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.

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''
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, 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, but specimens weighing up to have been recorded. Pacific cod are smaller than Atlantic cod and are darker in colour.

Distribution

live in the colder waters and deeper sea regions throughout the North Atlantic. Pacific cod is found in both eastern and western regions of the Pacific.
Atlantic cod could be further divided 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 habitats, 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, 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, the Irish Channel, 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.

Cod