Atlantic cod, Gadus morhua
See text for species.
Cod is the common name for various marine fish of the genus Gadus of the family Gadidae, and in particular the well-known food fish Gadus morhua, the Atlantic cod. The term cod also is used to refer to all members of the large marine family Gadidae, the cod family, which also includes haddocks, whitings, and pollocks (or pollacks).
Cod is commercially important, valued for its mild-flavored, white meat, which is low in fat, and for its liver oil. It has been a popular commercial fish for over a thousand years, helping in the fostering of cross cultural exchanges and trade networks, and the development in the east coast of North America in the seventeenth and eighteenth centuries is heavily tied to rich cod fishing grounds.
Cod also is important in marine food chains. Of the millions of eggs laid by a large female, few will reach adulthood to continue the life cycle, providing food for various fish and marine mammals along the way. However, this ecological harmony has been impacted by overfishing, and has led to depletion of cod stocks in various locations, including off the east coast of North America and in the North Sea.
The term cod also is used as the common name of a variety of other fishes in families other than Gadidae. However, this article will focus mainly on members of the Gadus genus.
Overview: Gadidae and Gadus
The cod family, Gadidae, is a family of marine fish, included in the order Gadiformes. It includes the cod (genus Gadus), haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), pollock or pollack (Pollachius genus), and some fish commonly called hakes (although there are several other families of hakes, such as merluccid hakes, family Merlucciidae, and the southern hakes, family Macruronidae), among others. Some other forms once included in this family here have since been removed to other families; on the other hand, the tadpole cod family Ranicipitidae has now been absorbed into Gadidae. (It only contains one species, the tadpole fish, Raniceps raninus.)
Members of the Gadidae family, like other Gadiformes, are characterized by the pelvic fins being below or in front of the pectoral fins and by being soft-rayed, with no true spines in the fins (Nelson 1994). The members of Gadidae have the first dorsal fin posterior to the head, the swim bladder not connected to the auditory capsules, and the head of the vomer is toothed (Nelson 1994). They are found in the Atlantic, Pacific, and Arctic Oceans.
Nelson (1994) listed the Gadidae family as having fifteen genera and thirty species. Twelve of these genera he recognizes as being in the cod and haddock subfamily Gadinae, including Melangrammus, Merlangius, Pollachius, as well as Gadus.
The Gadus genus comprises the "true cods." At various times in the past, a very considerable number of species have been classified in this genus. However the great majority of them are now either classified in other genera, or have been recognized as simply forms of one of three species. Modern taxonomy, therefore, recognizes only three species in this genus:
- Atlantic cod, Gadus morhua
- Pacific cod, Gadus macrocephalus
- Greenland cod, Gadus ogac
All these species have a profusion of common names, most of them including the word "cod." Many common names have been used of more than one species, in different places or at different times.
Cod forms part of the common name of many other fish that are not in the genus Gadus. Many of these are members of the family Gadidae, with several of these having been formerly classified in genus Gadus. Species that are commonly called cod that are not in the genus Gadus but that Nelson (1994) recognizes as within the family Gadidae include Arctic cod (Arctogadus glacialis), East Siberian cod (Arctogadus borisovi), Saffron cod (Eleginus gracilis), Polar cod (Boreogadus saida), and Poor cod (Trisopterus minutus).
Many other species with the common name cod are members of three related families whose names include the word "cod": the morid cods, Moridae (100 or so species); the eel cods, Muraenolepididae (4 species); and the Eucla cod, Euclichthyidae (1 species, Euclichthys polynemus, the Eucla cod). These families are all in the order Gadiformes.
Some other related fish have common names derived from "cod," such as codling, codlet, or tomcod. For example, members of the Gadiformes family Bregmacerotidae are known as codlets. "Codling" is also used as a name for a young cod.)
There are also many unrelated species called cod in other orders.
Description of species of Gadus
In addition to the characteristic Gadiformes structure with the pelvic fins located below or in front of the pectoral fins—unlike other fishes—the classic codfish shape has three rounded dorsal and two anal fins. Like other Gadiformes, the fins of members of the genus Gadus are soft-rayed. The pelvic fins are small with the first ray extended, and are set under the gill cover (i.e., the throat region).
In the three recognized species of Gadus, the upper jaw extends over the lower jaw, which has a well developed chin barbel. Codfish have medium sized eyes, approximately the same as the length of the chin barbel. It has 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 of Gadus species tends to be a greenish to sandy brown, and showing extensive mottling, especially towards the lighter sides and white belly. Dark brown coloration of the back and sides is not uncommon especially for individuals who have resided in rocky inshore regions. The Atlantic cod fish, which can change colors at certain depths of water, has two distinct color phases: gray-green and reddish brown.
The maximum size of any member of the family Gadidae is the Atlantic cod, Gadus morhua, which reaches a maximum length of about 1.8 meters (Nelson 1994). Its average weight is 10 to 25 pounds, but commonly reach 100 pounds and may reach 200 pounds.
Members of Gadus are common in the Northern Atlantic, including off the coast of Newfoundland, Labrador, Nova Scotia, New England, and Iceland. They are also found in other locales, including in the Pacific Ocean and Arctic Ocean.
In the western Atlantic Ocean, the Atlantic cod, Gadus morhua, has a distribution north of Cape Hatteras, North Carolina, and round both coasts of Greenland; in the eastern Atlantic it is found from the Bay of Biscay north to the Arctic Ocean, including the North Sea, areas around Iceland and the Barents Sea, which is the most important feeding area.
The Pacific cod, Gadus macrocephalus, is found mainly along the continental shelf and upper slopes with a range around the rim of the North Pacific Ocean, from the Yellow Sea to the Bering Strait, along the Aleutian Islands, and south to about Los Angeles, down to the depths of 900 meters.
The Greenland cod, Gadus ogac, inhabits inshore waters and continental shelves up to depths of 200 meters. Their range covers the Arctic Ocean and Northwest Atlantic Ocean from Alaska to West Greenland, then south along the Canadian coast to the Gulf of St. Lawrence and Cape Breton Island, generally from 45 to 75 degrees N.
Cod are gregarious and forms schools, although shoaling tends to be a feature of the spawning season.
Cod is an important link in the food chain. Adult cod are active hunters, feeding on sandeels, whiting, haddock, small cod, and with squid, crabs, lobsters, mussels, worms, mackerel, and mollusks supplementing their diets.
The Cod population comprises a number of reasonably distinct stocks over its range. These include the Arcto-Norwegian, North Sea, Faroe, Iceland, East Greenland, West Greenland, Newfoundland, and Labrador stocks. There would seem to be little interchange between the stocks, although migrations to their individual breeding grounds may involve distances of 200 miles or more.
Spawning occurs between January to April, with March and April the peak months. It occurs about at a depth of 200 meters in specific spawning grounds at water temperatures of between 4-6oC. Around the United Kingdom, the major ones are associated with 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.
Pre-spawning courtship involves fin displays, and male grunting, which leads to pairing. The male is inverted underneath the female, while the pair swim in circles during the spawning process. A large female lays more than a million eggs in mid-ocean.
The eggs are planktonic and hatch between 8 to 23 days with the larva being some 4 millimeters in length. This planktonic phase lasts some ten weeks, during which the young cod will increase its body weight by 40 times, and be about 2 centimeters in length. The young cod move to the seabed and their diet changes to small benthic crustaceans, such as isopods and small crabs. They increase in size to 8 centimeters in the first six months, 14 to 18 centimeters by the end of their first year, and some 25 to 35 centimeters by the end of the second. This rate of growth tends to be less in individuals occupying northerly grounds.
Few cod survive from egg to adult. Cod reach maturity at about 50 centimeters in length at about three to four-years-of-age.
Cod is a popular food fish with a mild flavor, low fat content, and a dense white flesh that flakes easily. Cod livers are processed to make cod liver oil, an important source of Vitamin A, Vitamin D, and omega-3 fatty acids (EPA and DHA).
Cod can be baked, broiled, fried, poached, or braised, and may be preserved by smoking, salting, or drying (Herbst 2001). Cod cheeks and tongues are considered delicacies, as well as young cod and haddock that weigh under 2.5 pounds (called scrod) (Herbst 2001).
In the United Kingdom, Atlantic cod is one of the most common kinds of fish to be found in fish and chips, along with haddock and plaice.
Cod is also well known for being popular in Portugal, where it is considered a treasure of the nation's cuisine.
Cod has been an important economic commodity in an international market since the Viking period (around 800 C.E.). Norwegians used dried cod during their travels and soon a dried cod market developed in southern Europe. This market has lasted for more than 1,000 years, passing through periods of Black Death, wars, and other crises and still is an important Norwegian fish trade (Barrett et al. 2000).
The Portuguese since the fifteenth century have been fishing cod in the North Atlantic and clipfish is widely eaten and appreciated in Portugal. The Basques also played an important role in the cod trade and are believed to have found the Canadian fishing banks before Columbus's discovery of America.
The North American east coast developed in part due to the vast amount of cod, and many cities in the New England area spawned near cod fishing grounds.
Apart from the long history, this particular trade also differs from most other trade of fish by the location of the fishing grounds, far from large populations and without any domestic market. 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 (Rolfsen 1966). Since the introduction of salt, dried salt cod ("klippfisk" in Norwegian) has also been exported. The trade operations and the sea transport were by the end of the fourteenth century taken over by the Hanseatic League, Bergen being the most important port of trade (Holt-Jensen 1985).
William Pitt the Elder, criticizing the Treaty of Paris in Parliament, claimed that cod was British gold; and that it was folly to restore Newfoundland fishing rights to the French.
In the seventeenth and eighteenth centuries, the New World, especially in Massachusetts and Newfoundland, cod became a major commodity, forming trade networks and cross-cultural exchanges. In the twentieth century, Iceland re-emerged as a fishing power and entered the Cod Wars to gain control over the north Atlantic seas.
In the late twentieth and early twenty-first centuries, cod fishing off the coast of Europe and America severely depleted cod stocks there, which has since become a major political issue as the necessity of restricting catches to allow fish populations to recover has run up against opposition from the fishing industry and concern about job losses. The 2006 Northwest Atlantic cod quota is set at 23,000 tons, representing half the available stocks, while it is set to 473,000 tons for the Northeast Atlantic cod.
The Pacific cod is currently enjoying a strong global demand. The 2006 TAC for the Gulf of Alaska and Berning Sea Aleutian Island was set at 574 million pounds.
In addition to cod being applied to various species within the genus Gadus and family Gadidae, there are also fish commonly known as cod that are quite unrelated to this genus or family, not being part of the order Gadiformes. Part of this confusion of names is market-driven. Since the decline in cod stocks has made the Atlantic cod harder to catch, cod replacements are marketed under names of the form "x cod," with culinary rather than phyletic similarity governing the emergence of these names. A very large number of fish have thus been named as some kind of cod at some time. The following species, however, seem to have well established common names including the word "cod." These all are Southern Hemisphere species.
Fish of the order Perciformes that are commonly called "cod" include:
- Murray cod Maccullochella peelii peelii
- Eastern freshwater cod Maccullochella ikei
- Mary River cod Maccullochella peelii mariensis
- Trout cod Maccullochella macquariensis
- Sleepy cod Oxyeleotris lineolatus
- Blue cod Parapercis colias
- The cod icefish family, Nototheniidae, including:
- Black cod Paranotothenia microlepidota
- Maori cod Paranotothenia magellanica
- Antarctic cod Dissostichus mawsoni
Rock cod, reef cod, and coral cod
Almost all the fish known as coral cod, reef cod, or rock cod are also in the 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 (or 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:
- Ling cod Ophiodon elongatus
- Red rock cod Scorpaena papillosa
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.
- Barrett, J., R. Beukens, I. Simpson, P. Ashmore, S. Poaps, and J. Huntley. 2000. What was the Viking age and when did it happen? A view from Orkney. Norwegian Archaeological Review 33(1).
- Clover, C. 2004. The End of the Line: How Overfishing Is Changing the World and What We Eat. London: Ebury Press. ISBN 0091897807.
- Herbst, S. T. 2001. The New Food Lover's Companion: Comprehensive Definitions of Nearly 6,000 Food, Drink, and Culinary Terms. Barron's Cooking Guide. Hauppauge, NY: Barron's Educational Series. ISBN 0764112589.
- Holt-Jensen, A. 1985. Norway and sea the shifting importance of marine resources through Norwegian history. GeoJournal 10(4).
- Kurlansky, M. 1997. Cod: A Biography of the Fish That Changed the World. New York: Walker. ISBN 0802713262.
- Nelson, J. S. 1994. Fishes of the World, 3rd edition. New York: John Wiley & Sons. ISBN 0471547131.
- Rolfsen, G. 1966. Norwegian fisheries Research. FiskDir. Skr. Ser. HavUnders 14(1): 36.
All links retrieved June 1, 2013.
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