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.
[4]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.
[5] Piranhas have also been discovered in the
Kaptai Lake in south-east
Bangladesh. Research is being carried out to establish how piranha 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.
Piranhas are normally about 14 to 26 cm long (6 to 10 inches), although some specimens have been reported to be up to 43 cm (18.0 inches) in length.
[7]Serrasalmus,
Pristobrycon,
Pygocentrus and
Pygopristis are most easily recognized by their unique
dentition. All piranhas have a single row of sharp teeth in both jaws; the teeth are tightly packed and interlocking (via small
cusps) and used for rapid puncture and shearing. Individual teeth are typically broadly triangular, pointed and blade-like (flat in profile). There is minor variation in the number of cusps; in most species, the teeth are tricuspid with a larger middle cusp which makes the individual teeth appear markedly triangular. The exception is
Pygopristis, which has pentacuspid teeth and a middle cusp usually only slightly larger than the other cusps. In the
scale-eating
Catoprion, the shape of their teeth is markedly different and the
premaxillary teeth are in two rows, as in most other serrasalmines.