Piranha

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 meaning fish and ánha meaning cut (which also meant "bad" or "devil" in Tupi-Guarani).[7]

Piranhas belong to the subfamily Serrasalminae, 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]

Piranha in Venezuela

Piranhas are indigenous to the Amazon basin, in the Orinoco, in rivers of the Guianas, in the Paraguay–Paraná, and the São Francisco River systems, but there are major differences in the species richness. In a review where 38–39 piranha species were recognized, 25 were from the Amazon and 16 from Orinoco, while only three were present in Paraguay–Paraná and two in São Francisco.[9] Most species are restricted to a single river system, but some (such as the red-bellied piranha) occur in several. Many species can occur together; for example, seven are found in Caño Maporal, a stream in Venezuela.[9]

Aquarium piranhas have been unsuccessfully introduced into parts of the United States.[10] 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).[11] 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.[12]

Close-up of a piranha at Georgia Aquarium

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 feeding on fish, piranha diets vary extensively,[3] leading to their classification as omnivorous.[4] In addition to fish (occasionally even their own species[20]), documented food items for piranhas include other vertebrates (mammals, birds, reptiles), invertebrates (insects, crustaceans), fruits, seeds, leaves and detritus.[3] The diet often shifts with age and size.[20] Research on the species Serrasalmus aff. brandtii and Pygocentrus nattereri in Viana Lake in Maranhão, which is formed during the wet season when the Pindaré River (a tributary of the Mearim River) floods, has shown that they primarily feed on fish, but also eat vegetable matter.[21] 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.[3] In a few species such as Serrasalmus serrulatus, the dietary split may be more equal, but this is less certain as based on smaller samples: Among 24 S. serrulatus from flooded forests of Ji-Paraná (Machado) River, there were several with fish remains in their stomachs, but half contained masticated seeds and in most of these this was the dominant item.[3] Piranhas will often scavenge,[9] and some species such as Serrasalmus elongatus are specialized scale-eaters, feeding primarily on scales and fins of other fish.[3] Scale- and fin-eating is more widespread among juvenile and sub-adult piranhas.[20]

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]

Fishing piranha on the Ucayali River

A piranha, lightly grilled, served as food in the Peruvian Amazon

A souvenir piranha

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 behavior has been documented among several South American tribes including the Camayura and Shavante in Brazil and the Pacahuara in Bolivia.[23][24][25] Piranhas are also popular as food. They are often considered a nuisance by fishers since they steal bait, eat catches, damage fishing gear and may bite when accidentally caught.[9]

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 destroyed to prevent proliferation in the latter.[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. It is not uncommon to find individual piranhas with one eye missing due to a previous attack.

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]

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]

• Animal bite
• Animal attack

Wikimedia Commons has media related to Serrasalminae.

• Piranha at Curlie
• Eric J. Lyman: "Piranha meat could take a bite out of what ails you", Houston Chronicle, 17 July 1998
• How to maintain healthy piranha in the home aquarium
• "Piranha Feeding Frenzy", National Geographic.com (2015-03-19)