Pupfish are a group of small killifish belonging to ten genera of the family Cyprinodontidae of ray-finned fish. All pupfish are especially noted for being found in extreme and isolated situations. They are primarily found in North America, South America, and the Caribbean region, but Aphanius are from southwestern Asia, northern Africa and southern Europe. As of August 2006 there were 120 known nominal species, and 9 subspecies.
The common name is said to derive from the mating habits of the males, whose activities vaguely resemble puppies at play.
In spite of their name, the cyprinodonts are not closely related to the Cyprinidae, or carp family. They were formerly considered near allies of the pikes and their relatives, as they share some features: a flat head with protractile mouth beset with cardiform, villiform, or compressed, bi- or tri-cuspid teeth, generally large scales, and the absence of a well-developed lateral line. However, they are now generally assigned to the order Cyprinodontiformes.
Most pupfish are inhabitants of the fresh and brackish waters. Several forms occur in the Oligocene and Miocene beds of Europe. Many species are ovoviviparous, and from their small size and lively behaviour they are much appreciated as aquarium fishes.
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