Piranha

Piranha Temporal range: Miocene–Recent PreꞒ Ꞓ O S D C P T J K Pg N
A red-bellied piranha at the Karlsruhe Zoo
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Characiformes
Family:	Serrasalmidae
Included genera
Catoprion Pristobrycon Pygocentrus Pygopristis Serrasalmus †Megapiranha

A piranha or piraña (

The name originates from the indigenous Tupi people and their respective Tupi language. It is formed from two words, pirá meaning fish and sainha meaning tooth; the same word is used by Indians to describe a pair of scissors.^[5] Another possible derivation is from pira nya, probably literally 'biting-fish'.^[6] In the mid 18th century the Portuguese merged the word into piranha. Finally, the word may also come from the combination of pirá 'fish' and ánha 'cut' (which also meant 'bad' or 'devil' in Tupi-Guarani).^[7]

Taxonomy and evolution

Piranhas belong to the family Serrasalmidae, which includes closely related omnivorous^[8] fish such as pacus.^[9] 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, 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.^[9]

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.^[9]

Distribution

Piranhas are indigenous to the

Piranhas have one of the strongest bites found in bony fishes. Relative to body mass, the black piranha (Serrasalmus rhombeus) produces one of the most forceful bites measured in vertebrates. This extremely powerful and dangerous bite is generated by large jaw muscles (adductor mandibulae) that are attached closely to the tip of the jaw, conferring the piranha with a mechanical advantage that favors force production over bite speed. Strong jaws combined with finely serrated teeth make them adept at tearing flesh.^[18]

Ecology

Piranhas vary extensively in ecology and behavior depending on exact species.^[3] Piranhas, especially the red-bellied (Pygocentrus nattereri), have a reputation as ferocious predators that hunt their prey in schools. Recent research, however, which "started off with the premise that they school as a means of cooperative hunting", discovered they are timid fish that schooled for protection from their own predators, such as cormorants, caimans, and dolphins. Piranhas are "basically like regular fish with large teeth".^[19] A few other species may also occur in large groups, while the remaining are solitary or found in small groups.^[3]

Although popularly described as highly predatory and primarily

Piranhas lay their eggs in pits dug during the breeding season and swim around to protect them. Newly hatched young feed on zooplankton, and eventually move on to small fish once large enough.^[22]

Relationship with humans

Piranha teeth are often used as tools themselves (such as for carving wood or cutting hair) or to modify other tools (such as sharpening of

Piranhas can be bought as pets in some areas, but they are illegal in many parts of the United States, and in the Philippines, where importers face six months to four years in jail, and the piranhas are destroyed to prevent proliferation.^[26][27]

The most common aquarium piranha is Pygocentrus nattereri, the red-bellied piranha. Piranhas can be bought fully grown or as young, often no larger than a thumbnail. It is important to keep Pygocentrus piranhas alone or in groups of four or more, not in pairs, since aggression among them is common, not allowing the weaker fish to survive, and is distributed more widely when kept in larger groups.^{[citation needed]} It is not uncommon to find individual piranhas with one eye missing due to a previous attack.

Attacks

Although often described as extremely dangerous in the media, piranhas typically do not represent a serious risk to humans.^[3][28] However, attacks have occurred, especially when the piranhas are in a stressed situation such as the dense groups that may occur when the water is lower during the dry season and food is relatively scarce.^[3][29] Swimming near fishermen may increase the risk of attacks due to the commotion caused by struggling fish and the presence of bait in the water.^[30][31] Splashing attracts piranhas and for this reason children are more often attacked than adults.^[29] Being in the water when already injured or otherwise incapacitated also increases the risk.^[3] There are sometimes warning signs at high-risk locations^[32] and beaches in such areas are sometimes protected by a barrier.^[33]

Most piranha attacks on humans only result in minor injuries, typically to the

Various stories exist about piranhas, such as how they can skeletonize a human body or cattle in seconds. These legends refer specifically to the red-bellied piranha.^[40]

Piranha solution, a dangerous mixture of sulfuric acid and hydrogen peroxide known to aggressively dissolve organic material, draws its name from these legends surrounding the piranha fish.

A common falsehood is that they can be attracted by blood and are exclusively carnivores.^[41] A Brazilian legend called "piranha cattle" states that they sweep the rivers at high speed and attack the first of the cattle entering the water allowing the rest of the group to traverse the river.^[42] These legends were dismissed through research by Hélder Queiroz and Anne Magurran and published in Biology Letters.^[43]

Accounts from Theodore Roosevelt

When former US President

• Animal bite
• Animal attack

References