Piranhas belong to the subfamily Serrasalminae, which includes closely related omnivorous[3] fish such as pacus.[4] Traditionally, only the fourgenera Pristobrycon, Pygocentrus, Pygopristis and Serrasalmus are considered to be true piranhas, due to their specialized teeth. However, a recent analysis showed that, if the piranha group is to be monophyletic, it should be restricted to Serrasalmus, Pygocentrus and part ofPristobrycon, 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.[4]
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.[4]
Distribution Piranhas are indigenous to the Amazon basin, in the Orinoco, in rivers of the Guyanas, in theParaguay-Paraná, and the São Francisco River systems.
Aquarium piranhas have been introduced into parts of the United States, with specimens occasionally found in the Potomac River, Lake of the Ozarks in Missouri and even as far north as Lake Winnebago inWisconsin, although they typically do not survive cold winters.[5] Two girls fishing in a pond on Staten Island, New York City, caught a red-bellied piranha.[6] 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 anti-poaching forces. Piranhas were also spotted in the Lijiang River in China.[7]
Description
Piranhas are normally about 14 to 26 cm long (5.5 to 10.25 inches), although some specimens have been reported to be up to 43 cm (17.0 inches) in length.[8]
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). There is minor variation in the number of cusps; 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.
Ecology
Piranha 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 that 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".[9]
IT shown that these species eat vegetable matter at some stages in their life; they are not strictly carnivorous fish.[10]
Piranhas lay their eggs in pits dug during the breeding and swim around to protect them. Newly hatched young feed on zooplankton, and eventually move on to small fish once large enough.[11]
Relationship with humans
Piranha teeth are often used to make tools and weapons by the indigenous population. Piranhas are also popular as food, although if an individual piranha is caught on a hook or line, it may be attacked by others.[citation needed]
Piranhas can be bought as pets in some areas, but they are illegal in many parts of the United States.[12] It is illegal to import piranhas into thePhilippines and violators could face six months to four years of jail.[13]
The most common aquarium piranha is Pygocentrus nattereri, the red-bellied piranha. Piranhas can be bought fully grown or as babies, 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 rare to find individuals with one eye missing due to a previous attack.
Attacks
Attacks resulting in deaths are recurring in the Amazon basin. In 2011 a drunk eighteen-year-old man was attacked and killed in Rosario del Yata,Bolivia.[14] In 2012, a five-year-old Brazilian girl was attacked and killed by a shoal of Pygocentrus nattereri.[15] Some Brazilian rivers have warning signs about lethal piranhas.[16] In 2011, in the Brazilian state of Piauí, there were brutal and recurring attacks resulting in one hundred people being injured.[17]In the State of São Paulo another attack in the Tietê river resulted in 15 injured people.[18] In the city of Palmas, Tocantins, 190 piranha attacks were reported in the first half of 2007.[19] Biologists and experts warn that entering unknown rivers can be dangerous and fatal. Contrary to what many think, piranhas can be found in all regions of Brazil, including rivers, lakes,and coastal areas.
Legendary reputation
There are various myths about piranhas such as how they can dilacerate a human body or cattle in seconds. These myths refer specifically toPygocentrus nattereri, the red-bellied piranha.[20] A recurrent myth is that they can be attracted by blood and are exclusive carnivores.[21] A Brazilian myth 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.[22] These myths were dismissed through research by Helder Queiroz and Anne Magurran and published on Biology Letters.[23] Nevertheless, a study in Suriname found that piranhas may occasionally attack humans, particularly when water levels are low.[24]
Theodore Roosevelt
They are the most ferocious fish in the world. Even the most formidable fish, the sharks or the barracudas, usually attack things smaller than themselves. But the piranhas habitually attack things much larger than themselves. They will snap a finger off a hand incautiously trailed in the water; they mutilate swimmers—in every river town in Paraguay there are men who have been thus mutilated; they will rend and devour alive any wounded man or beast; for blood in the water excites them to madness. They will tear wounded wild fowl to pieces; and bite off the tails of big fish as they grow exhausted when fighting after being hooked.But the piranha is a short, deep-bodied fish, with a blunt face and a heavily undershot or projecting lower jaw which gapes widely. The razor-edged teeth are wedge-shaped like a shark’s, and the jaw muscles possess great power. The rabid, furious snaps drive the teeth through flesh and bone. The head with its short muzzle, staring malignant eyes, and gaping, cruelly armed jaws, is the embodiment of evil ferocity; and the actions of the fish exactly match its looks.I never witnessed an exhibition of such impotent, savage fury as was shown by the piranhas as they flapped on deck. When fresh from the water and thrown on the boards they uttered an extraordinary squealing sound. As they flapped about they bit with vicious eagerness at whatever presented itself. One of them flapped into a cloth and seized it with a bulldog grip. Another grasped one of its fellows; another snapped at a piece of wood, and left the teeth-marks deep therein. They are the pests of the waters, and it is necessary to be exceedingly cautious about either swimming or wading where
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