Cod, common name for nearly 60 species of valuable food fish of the family Gadidae, order Gadiformes. Other families in the order are also known as cod, such as the deep-sea cod of the family Moridae, but the best-known and most commercially important cod is the Atlantic cod, Gadus morhua, of the Gadidae. Cod live chiefly in cold or temperate northern seas, at depths of 180 to 360 m (600 to 1200 ft), and undertake long migrations. Many live near the bottom.

The Atlantic cod has three dorsal fins, two anal fins, an unforked tail, and a small barbel on its lower jaw. It is generally moderate in size but can weigh as much as 90 kg (200 lb) and be as long as 1.8 m (6 ft). Greenish-gray to blackish-brown and sometimes red, it has a marbled pattern on its head, back, and sides. It is a voracious predator, eating herring, sand eel, and other shoal fishes. The cod gather in large numbers during the winter months to spawn, and each female lays 4 to 7 million eggs. Every egg has a droplet of oil so that it floats, and the larval cod become part of the plankton for about 10 weeks. They sink to the bottom when they are about 2 cm (about 1 in) long, begin to migrate in the second year, and spawn in five years.

Cod are valued both as food and as the source of cod-liver oil. They form the basis of a historically profitable fishery in the North Atlantic, to which England, France, and Portugal began to send boats yearly in the 16th century. The crews camped on the beaches during their stay and dried the fish before sending their catch back to Europe. Such fishing is still an important part of the economy in countries such as Iceland and Great Britain. Thinning of the fish stocks has made the remaining sources vital enough to cause aggressive competition.

Other commercially important species of the Gadidae include the pollack, Pollachium virens; the Pacific cod, G. macrocephalus, greatly valued by the Japanese; the haddock, Melanogrammus aeglefinus; and the tomcod genus, Microgadus. Haddock, in particular, have been overfished by large stern- trawling factory ships.

Information provided by: http://cnet.windsor.ns.ca