Atlantic cod, Gadus morhua
Gadidae is a family of almost exclusively marine fish in the order Gadiformes, characterized by the first dorsal fin being posterior to the head, the lack of true spines in the fins, and most with long dorsal and anal fins. Known as the "cod family," Gadidae includes cods, haddocks, whiting, pollock, and, in some taxonomic schemes, the cuskfishes. The familiar cods and haddocks are characterized by three dorsal fins and two anal fins. Members of Gadidae are found in the Arctic, Atlantic, and Pacific Oceans, with one of the cuskfishes a freshwater species.
Members of Gadidae provide important ecological and commercial values. Ecologically, they are important in food chains. With large females of some species producing millions of eggs, they provide food for many fish, offering a higher level function for the ecosystem while also advancing an individual level function of reproduction. As such, they reflect the principle of bi-level functionality.
The high reproductive rate of species like cod and haddock, combined with their mild-flavored, low-fat meat, has led to their being a very important target of commercial fishing. Cod also is prized as a source of cod liver oil.
Gadiformes, the order in class Actinopterygii to which Gadidae belongs, includes many fish of commercial importance, constituting over one quarter of the marine fish catch of the world (Nelson 2006). Members of Gadiformes are characterized by the pelvic fins (when presence) having up to 11 rays and being below or in front of the pectoral fins, generally long dorsal and anal fins, no true spines in the fins, usually cycloid (rarely ctenoid) scales, and a swim bladder without pneumatic duct (Nelson 2006).
Gadidae, the cod family, has about 16 genera and 31 species according to the classification used by Nelson (2006). According to his system, members of Gadidae are characterized by having the first dorsal fin posterior to the head, the head of the vomer toothed, and the swim bladder not connected with auditory capsules. Nelson places the members of Gadiformes into three subfamilies: Lotinae (cuskfishes), Gadinae (cods and haddocks), and Ranicipitinae (tadpole cods). However, different classification schemes are recognized, including those that elevate the first two subfamilies to the family level, and even some that elevate the third subfamily to family status.
Members of Gadinae subfamily, which some elevate to family status (as Gadidae), is characterized by having three dorsal and two anal fins, an egg without an oil globule, usually a chin barbel, and a slightly forked or truncate caudal fin (Nelson 2006). This subfamily includes the cods, haddocks, pollocks, and the whiting (Merlangius merlangus). Twelve genera are included in this subfamily, with about 25 species. Note that P. pollachius, one of the two species known as pollocks (or pollacks) lacks a chin barbel.
Members of the Lotinae subfamily, which some also elevate to family status, is characterized by having one or two dorsal fins and one anal fin. Members of this subfamily always have a chin barbel, but there are not barbels on the snout. The caudal fin is rounded and the egg has an oil globule. Known as the cuskfishes, there are five species in the taxon, which are arranged into three genera.
The subfamily Ranicipitinae has only one extant member, the tadpole cod (Raniceps raninus). It has two dorsal fins with the first dorsal fin having three short rays, one anal fin with a long base, the head without pores or a lateral line, a chin barbel present, and the upper jaw protruding beyond the lower. Most authors place it in Gadidae, although some place it in its own family (Nelson 2006).
ITIS (2004a) recognizes yet another subfamily within Gadidae, along with Gadinae and Lotinae. This is Phycinae, the phycine hakes.
Members of Gadidae are generally medium sized fish. Almost all species have barbels on their chin (all Lotinae, almost all Gadidae, and the tadpole cod). This barbel is used while browsing on the sea floor. Gadids are carnivorous, feeding on smaller fish and crustaceans.
Gadids tend to be highly prolific, with many species producing several million eggs at each spawning. This contributes to their high population numbers, which, in turn, makes commercial fishing relatively easy (Cohen 1998).
Only one species, Lota lota, the burbot, is a completely freshwater member of the family and order. It is found in northern parts of North America and Eurasia. The burbot is part of the subfamily Lotinae (cuskfishes). Other members of Lotinae are marine and found in the northern Atlantic.
Members of the Gadinae subfamily (which a number of authorities place at the family level, with the cuskfishes in their own family) are marine and found in the Arctic, Atlantic, and Pacific Oceans. There is one member, Microgadus tomcod, that is marine (off the Atlantic coast of North America) but can spawn in freshwater, and some freshwater populations are known (Nelson 2006).
The tadpole cod, Ranicpes raninux, in subfamily Ranicipitinae, is found in shallow coastal waters of the northeatern Atlantic, from the Norwegian coast to the the Bay of Biscay and the British Isles (Nelson 2006).
The following taxonomy follows (Nelson 2006). However, as noted above, many authorities raise Gadinae to the family level, and the cuskfishes (subfamily Lotinae) then are removed from the Gadidae family. While the Ranicipinae subfamily is sometimes made into its own family, generally its one extant member, Rancipes raninus is considered part of Gadidae whether or not Gadinae is raised to the family level. When Gadinae is raised to the family level, some authorities recognize several other subfamilies within Gadidae (Nelson 2006).
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