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''Atlantic herring Clupea harengus
one of the most abundant species in the world

A fish is a poikilothermic water-dwelling vertebrate with gills. Fishes (over 27,315 species) are a paraphyletic group and are divided into the bony fishes (class Osteichthyes, 22,000 species); cartilaginous fishes (class Chondrichthyes, 800 species); and various groups of jawless fishes (75 species), including lampreys and hagfish. Fishes come in different sizes, from a 45 foot whale shark to a 8 mm long dwarf goby. Other aquatic animals, such as jellyfish and cuttlefish, are not true fish.

Table of contents
1 Note on usage: fish vs. fishes
2 Fish ecology
3 See also
4 External links

Note on usage: fish vs. fishes

Fishes is the proper English plural form of fish that biologists use when speaking about two or more fish species, as in "There are over 25,000 fishes in the world" (meaning that there are over 25,000 fish species in the world). When speaking of many fish that all are part of the same species, then the word "fish" is used, as in "There are several million fish in the species Gadus morhua."

Fish ecology

Fishes can be found in most all large bodies of water in either salt and fresh water, at depths ranging from just below the surface to several thousand meters. However, hyper-saline lakes like the Great Salt Lake do not support fish. Some species of fish have been specially bred to be kept and displayed in an aquarium.

Fish are an important source of food. Other water-dwelling animals such as mollusks and crustaceans (commonly called shellfish) are often considered as fish when used as food. Catching fish for the purpose of food or sport is known as fishing. The annual yield from all fisheries worldwide is about 100 million tonnes.

Overfishing is a threat to many species of fish. On May 15, 2003, the journal Nature reported that all large oceanic fish species worldwide had been so systematically overcaught that fewer than 10% of 1950 levels remained. [1] Particularly imperilled were sharks, Atlantic cod, and Pacific sardines. The authors recommended immediate, drastic cutbacks in fish catches and reservation of ocean habitats worldwide.

Black sea bass Centropristis striata (photo: Uwe Kils)

See also

External links