Introduction

The piranha is an omnivorous fish that inhabits South American rivers, floodplains, lakes, and reservoirs. Despite its reputation as a highly predatory fish, its diverse diet includes plant material.

Etymology

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; Indians use the same word 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).

Taxonomy

Piranhas belong to the family Serrasalmidae, which includes closely related omnivorous fish such as pacus. Due to their specialized teeth, traditionally, only the four genera, Pristobrycon, Pygocentrus, Pygopristis, and Serrasalmus, are considered true piranhas. However, a recent analysis showed that 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 more closely related to Catoprion than the other three piranha genera.

The 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.

Distribution

Piranhas are indigenous to the Amazon basin, in the Orinoco, the rivers of the Guianas, the Paraguay–Paraná, and the São Francisco River systems. Still, there are significant 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. 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.

Aquarium piranhas have been unsuccessfully introduced into parts of the United States. 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 away from their original habitat to such distant corners of the world. Some rogue exotic fish traders are thought to have released them into the lake to avoid being caught by antipoaching forces. Piranhas were also spotted in the Lijiang River in China.

Size

Depending on the species, most piranhas grow between 12 and 35 cm (5–14 in) long. A few can grow more extensive, with the largest living species, the red-bellied, reaching up to 50 cm (20 in). There are claims of São Francisco piranhas at up to 60 cm (24 in), but the largest confirmed specimens are considerably smaller. The extinct Megapiranha, which lived 8–10 million years ago, reached about 71 cm (28 in) long, possibly even 128 cm (50 in).

Morphology

Their unique dentition most easily recognizes Serrasalmus, Pristobrycon, Pygocentrus, and Pygopristis. 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 more prominent 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.

Biting abilities

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 mighty and dangerous bite is generated by large jaw muscles (adductor mandibulae) 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.

Ecology

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

Although popularly described as highly predatory and primarily feeding on fish, piranha diets vary extensively, leading to their classification as omnivorous. In addition to fish (occasionally even their species), documented food items for piranhas include other vertebrates (mammals, birds, reptiles), invertebrates (insects, crustaceans), fruits, seeds, leaves, and detritus. The diet often shifts with age and size. 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. In another study of more than 250 Serrasalmus rhombus at Ji-Paraná (Machado) River, 75% to 81% (depending on the season) of the stomach content was fish, but about 10% was fruits or seeds. 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. In most of these, this was the dominant item. Piranhas will often scavenge, and some species, such as Serrasalmus elongatus, are specialized scale-eaters, feeding primarily on the scales and fins of other fish. Scale- and fin-eating is more widespread among juvenile and sub-adult piranhas.

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.

Relationship with humans

Piranha teeth are often used as tools (such as for carving wood or cutting hair) or to modify other tools (such as sharpening darts). This behavior 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. Fishers often consider them a nuisance since they steal bait, eat catches, damage fishing gear, and may bite when accidentally caught.

Piranhas can be bought as pets in some areas. Still, 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.

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 essential to keep Pygocentrus piranhas alone or in groups of four or more, not in pairs, since aggression among them is expected, not allowing the weaker fish to survive, and is distributed more widely when kept in larger groups. It is hoped to find individual piranhas missing one eye 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. However, attacks have occurred, especially when the piranhas are in a stressful situation, such as the dense groups that may arise 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. Splashing attracts piranhas, and for this reason, children are more often attacked than adults. Being in the water when already injured or incapacitated also increases the risk. There are sometimes warning signs at high-risk locations, and a barrier occasionally protects beaches in such areas.

Most piranha attacks on humans only result in minor injuries, typically to the feet or hands, but they are occasionally more severe and very rarely can be fatal. Near Palmas in Brazil, 190 piranha attacks, all involving single bites to the feet, were reported in the first half of 2007 in an artificial lake that appeared after the damming of the Tocantins River. In the state of São Paulo, a series of attacks in 2009 on 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 struck and killed in Rosario del Yata, Bolivia. In 2012, a five-year-old Brazilian girl was attacked and destroyed 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 the bodies of people who already have died, such as drowning victims.

Reputation

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 dissolve organic material aggressively, draws its name from these legends surrounding the piranha fish.

A common falsehood is that blood can attract them and are exclusively carnivores. A Brazilian legend called “piranha cattle” states that they sweep the rivers at high speed and attack the first 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.

Our Object

Size (W x H)

17 x 7 cm

Location

S.6

Classification

Coll#1

Provenance

We purchased the taxidermied fish from an experienced oddities seller 15 years ago. The item came with a receipt from the original buyer, who visited the Amazon in the 1980s and bought the fish as a souvenir.