Piranhas belong to the sub-family Serrasalminae, which also includes closely related most omnivorous fish such as pacus. Traditionally, only the four genera Pristobrycon, Pygocentrus, Pygopristis and Serrasalmus are considered to be true piranhas, due to their specialized teeth. However, a recent analysis showed that, if the piranha group is to be monophyletic, it should be restricted to Serrasalmus, Pygocentrus and part of Pristobrycon, or expanded to include these taxa plus Pygopristis, Catoprion, and Pristobrycon striolatus. Pygopristis was found to be more closely related to Catoprion than the other three piranha genera.
The total number of piranha species is unknown and contested and new species continue to be described. Estimates range from fewer than 30 to more than 60.
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Where i can see Piranhas?
Piranhas are found in the Amazon basin, in the Orinoco, in rivers of the Guyanas, in the Paraguay-Paraná, and the São Francisco River systems. Some species of piranha have broad geographic ranges, occurring in more than one of the major basins mentioned above, whereas others appear to have more limited distributions.
Aquarium piranhas have been introduced into parts of the United States with specimens occasionally found in the Potomac River and even as far north as Lake of the Ozarks in Missouri and Lake Winnebago in Wisconsin, although they typically do not survive cold winters. Piranhas have also been discovered in the Kaptai Lake in south-east Bangladesh, Chalakudy River in Kerala, South India. Research is being carried out to establish how piranhas have moved to such distant corners of the world from their original habitat. It is anticipated that some rogue exotic fish traders have released them in the lake to avoid being caught by anti-poaching forces.