Fish

For other uses, see Fish (disambiguation).

Atlantic herring, Clupea harengus: the most abundant species of fish in the world.

A fish is a poikilothermic (cold-blooded) water-dwelling vertebrate with gills. There are over 27,000 species of fish, making them the most diverse group of vertebrates. Taxonomically, fish are a paraphyletic group whose exact relationships are much debated; a common division is into the jawless fish (class Agnatha, 75 species including lampreys and hagfish), the cartilaginous fish (class Chondrichthyes, 800 species including sharks and rays), with the remainder classed as bony fish (class Osteichthyes).

Fish come in different sizes, from the 16m (51 ft) whale shark to a 7 mm (just over 1/4 of an inch) long stout infantfish. Many types of aquatic animals named "fish", such as jellyfish and cuttlefish, are not true fish. Other sea dwelling creatures, like dolphins, are actually mammals.

Certain species of fish maintain elevated body temperatures to varying degrees. Endothermic teleosts (bony fishes) are all in the suborder Scombroidei and include the billfishes, tunas, and one species of "primitive" mackerel (Gasterochisma melampus). All sharks in the family Lamnidae – shortfin mako, long fin mako, white, porbeagle, and salmon shark – are known to have the capacity for endothermy, and evidence suggests the trait exists in family Alopiidae (thresher sharks). The degree of endothermy varies from the billfish, which warm only their eyes and brain, to bluefin tuna and porbeagle sharks who maintain body temperatures elevated in excess of 20 °C above ambient water temperatures. See also gigantothermy. Endothermy, though metabolically costly, is thought to provide advantages such as increased contractile force of muscles, higher rates of central nervous system processing, and higher rates of digestion.

Fish ecology

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

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 over caught that fewer than 10% of 1950 levels remained. [1] Particularly imperiled were sharks, Atlantic cod, Bluefin tuna, and Pacific sardines. The authors recommended immediate drastic cutbacks in fish catches and reservation of ocean habitats worldwide.

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 two or more individual fish organisms, then the word "fish" is used, as in "There are several million fish of the species Gadus morhua" (meaning that G. morhua comprises several million individuals). To see both in action, consider the statement "There are twelve fish in this aquarium, representing five fishes" (meaning that the aquarium contains twelve individuals, some of the same species and some of different species, for a total of five species). The usage of the two words is similar to that of the words "people" and "peoples".

Fish as food

Fishes are an important source of food in many cultures. Other water-dwelling animals such as mollusks, crustaceans, and shellfish are often called "fish" when used as food. For more details, see Fish (food).

Centropristis striata

Classification

Fish are a paraphyletic group: that is, any clade containing all fish also contains the tetrapods, which are not fish. Fish are classified into the following major groups:

• Conodonta
• Hyperoartia
  • Petromyzontidae (lampreys)
• Pteraspidomorphi (early jawless fish)
• Thelodonti
• Anaspida
• Cephalaspidomorphi (early jawless fish)
  • Galeaspida
  • Pituriaspida
  • Osteostraci
• Gnathostomata (jawed vertebrates)
  • Placodermi
  • Chondrichthyes (cartilaginous fish)
  • Acanthodii
  • Osteichthyes (bony fish)
    • Actinopterygii (ray-finned fish)
    • Sarcopterygii (lobe-finned fish)
      • Actinistia (coelacanths)
      • Dipnoi (lungfish)

For a fuller treatment of classification, see the vertebrate article.

See also

• The Wikipedia Fish Category page which provides links to all aspects of the subject from icthyology to aquariums to sharks.

• Animal
• Aquarium
• Deep sea fish
• Fish anatomy
• Fish farming
• Fish migration
• Fish (singer)
• Fishing
• Ichthyology (the study of fish)
• List of fish families
• List of fish common names
• List of freshwater aquarium fish species
• Marine aquarium fish species
• Fishing Light Attractors
• Oily fish
• Ostracoderm - the first fishes
• Prehistoric fish
• Shoal - the collective noun for fish (also school)
• White fish
• Fish locomotion

External links

• 70South - information on Antarctic fish
• A World of Fish Species information and fish care
• Fish database (FishBase)
• Join Ray Mullet in the Fish Olympics!
• Project for children - build a fish mobile with a behavior
• Fish Keeping
• Site with one of the largest fish databases in the world
• Reelinthefish.net | Interview with Dr James K. Oliver, Reefbase Scientist
• Fishy.UsArticles & Particles
• Saltwater & Freshwater Forums
• Help on raising Aquarium Fish
• Aquarium Fish Education
• Fish and Seafood RecipesCooking With Fish
• Reef aquarium community and learning center
• German Educator in Fisheries, Specialist in Fancy Goldfish and Fishhealth, with Forum and large Picture-Gallery
• Fish Aquarium simulator for mac.
• AroFanaticsWebsite one of the most popular fish-keeping forum.
• The Aquarium Fish Tank Friend
• Information about fish - Wild Animals Online encyclopedia
• Minnesotas Foremost Fishing, Hunting, and Outdoor Community - Read Stories, Download our Newsletter, Join our Club!Template:Link FA