Пираньи: Описание, происхождение и виды

Common name for certain fishes of the family Serrasalmidae

A piranha or piraña (/p//ᵻ/'/r//ɑː//n//j//ə//,// // //r//æ//n/, or /p//ᵻ/'/r//ɑː//n//ə/; piˈɾɐ̃ɲɐ, piˈɾaɲa) is any of a number of freshwater fish species in the family Serrasalmidae, or the subfamily Serrasalminae within the tetra family, Characidae in order Characiformes. These fish inhabit South American rivers, floodplains, lakes and reservoirs. Although often described as extremely predatory and mainly feeding on fish, their dietary habits vary extensively, and they will also take plant material,

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. Another possible derivation is from pira nya, probably literally 'biting fish'. 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).

Piranhas belong to the family Serrasalmidae, which includes closely related 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, 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. In many cases, however, reported captures of piranhas are misidentifications of pacu (e. g., red bellied pacu or Piaractus brachypomus is frequently misidentified as red bellied piranha or Pygocentrus nattereri). Piranhas have also been discovered in the Kaptai Lake in southeast Bangladesh. Research is being carried out to establish how piranhas have moved to such distant corners of the world from their original habitat. Some rogue exotic fish traders are thought to have released them in the lake to avoid being caught by antipoaching forces. Piranhas were also spotted in the Lijiang River in China.

Depending on the exact species, most piranhas grow to between long. A few can grow larger, with the largest living species, the red bellied, reaching up to There are claims of São Francisco piranhas at up to , but the largest confirmed specimens are considerably smaller. The extinct Megapiranha which lived 8–10 million years ago reached about long, and possibly even .

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 are used for rapid puncture and shearing. Individual teeth are typically broadly triangular, pointed, and blade like (flat in profile). The variation in the number of cusps is minor. 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.

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.

Piranhas vary extensively in ecology and behavior depending on exact species. A few other species may also occur in large groups, while the remaining are solitary or found in small groups. ), documented food items for piranhas include other vertebrates (mammals, birds, reptiles), invertebrates (insects, crustaceans), fruits, seeds, leaves and detritus. In another study of more than 250 Serrasalmus rhombeus at Ji Paraná (Machado) River, 75% to 81% (depending on season) of the stomach content was fish, but about 10% was fruits or seeds.

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 darts). This practice has been documented among several South American tribes including the Camayura and Shavante in Brazil and the Pacahuara in Bolivia. Piranhas are also popular as food, though they are often considered a nuisance by fishers because they steal bait, eat catches, damage fishing gear, and may bite when accidentally caught. 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. It is not uncommon to find individual piranhas with one eye missing due to a previous attack.

Although often described as extremely dangerous in the media, piranhas typically do not represent a serious risk to humans. 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. 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. and beaches in such areas are sometimes protected by a barrier. Most piranha attacks on humans only result in minor injuries, typically to the feet or hands, but they are occasionally more serious and very rarely can be fatal. In the state of São Paulo, a series of attacks in 2009 in the Tietê River resulted in minor injuries to 15 people. In 2011, another series of attacks at José de Freitas in the Brazilian state of Piauí resulted in 100 people being treated for bites to their toes or heels. On 25 December 2013, more than 70 bathers were attacked at Rosario in Argentina, causing injuries to their hands or feet. In 2011, a drunk 18 year old man was attacked and killed in Rosario del Yata, Bolivia. In 2012, a five year old Brazilian girl was attacked and killed by a shoal of P. nattereri. In January 2015, a six year old girl was found dead with signs of piranha bites on part of her body after her family canoe capsized during a vacation in Monte Alegre, Brazil. Whereas fatal attacks on humans are rare, piranhas will readily feed on bodies of people that already have died, such as drowning victims.

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. 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. 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. These legends were dismissed through research by Hélder Queiroz and Anne Magurran and published in Biology Letters.

When former US President Theodore Roosevelt visited Brazil in 1913, he went on a hunting expedition through the Amazon Rainforest. While standing on the bank of the Amazon River, he witnessed a spectacle created by local fishermen. After blocking off part of the river and starving the piranhas for several days, they pushed a cow into the water, where it was quickly torn apart and skeletonized by a school of hungry piranhas. Roosevelt later described piranhas as vicious creatures in his 1914 book Through the Brazilian Wilderness.