Piranha means scissors in Old Tupi—and myths outrun the bite
Piranhas are South American freshwater serrasalmids often cast as extreme predators, though many are less ferocious than folklore claims. The name traces to Old Tupi pirãîa, attested in a 1585 Portuguese–Tupi dictionary as “scissors,” applied to the fish soon after.
Piranhas are freshwater fish of the subfamily Serrasalminae, family Serrasalmidae, order Characiformes, living in South American rivers, floodplains, lakes and reservoirs. Their fearsome reputation as fish-eating hunters is only part of the story: diets vary widely and many also eat plant matter, so they are classed as omnivores. Its name derives from Old Tupi pirãîa, which a Portuguese-Tupi wordbook of 1585 glosses as scissors. Gabriel Soares de Sousa applied it to the fish in his 1587 treatise Noticia do Brasil, and English borrowed it from Portuguese in 1710, alongside the variants piraña and the archaic piraya.
Which fish count as true piranhas is unsettled. Traditionally four genera with specialised teeth qualified: Pristobrycon, Pygocentrus, Pygopristis and Serrasalmus. A recent analysis found that for the group to share a single ancestor it must either shrink to Serrasalmus, Pygocentrus and part of Pristobrycon, or grow to include Catoprion too. Newer treatments give the name to almost every member of the subfamily except its most basal genus, Metynnis, the silver dollars. Their close relatives the pacus are omnivores. Species counts range from under 30 to over 60, and new ones are still being described.
The fish are native to the Amazon, Orinoco, Guianas, Paraguay-Parana and Sao Francisco systems, but unevenly: one review recognising 38 to 39 species placed 25 in the Amazon and 16 in the Orinoco, against three in the Paraguay-Parana and two in the Sao Francisco. Most species keep to one river system, though the red-bellied piranha ranges more widely, and seven species share one Venezuelan stream, Caño Maporal. Released aquarium fish have failed to establish in the United States, where many reported catches turn out to be pacus. Piranhas have also appeared in Bangladesh's Kaptai Lake, possibly dumped by traders, and in China's Lijiang River.
Most species grow to between 12 and 35 cm. The red-bellied piranha, the largest living species, reaches up to 50 cm, and claims of 60 cm Sao Francisco fish remain unconfirmed. The extinct Megapiranha, which lived 8 to 10 million years ago, reached about 71 cm and possibly much more.
Source: Piranha
