A piranha or piraña
is a member of a family of omnivorous freshwater fish which live in South American rivers. In Venezuelan rivers, they are called caribes. They are known for their sharp teeth and a voracious appetite for meat.[You must be registered and logged in to see this image.] Taxonomy
Piranhas belong to the subfamily Serrasalminae, which also includes closely related herbivorous 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 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 found to be more closely related to Catopricornis than the other three piranha genera.The total number of piranha species is unknown and new species continue to be described. In 1988, it was stated that fewer than a half of the approximately 60 nominal species of piranhas at the time were valid. More recently (in 2003), one author recognized a total of 38 or 39 species, although the validity of some taxa remains questionable. Distribution
Piranhas are found in the Amazon basin, in the Orinoco, in rivers of the Guyanas, in the Paraguay-Paraná, and the Sãn Francisco River systems. Some species of piranha have broad geographic ranges, occurring in more than one of the major basins mentioned above, whereas others appear to have more limited distributions.
Aquarium piranhas have been introduced into parts of the United States with specimens occasionally found in the Potomac River and even as far north as Lake of the Ozarks in Missouri and Lake Winnebago in Wisconsin, although they typically do not survive cold winters.Piranhas have also been discovered in the Kaptai Lake in south-east Bangladesh. Research is being carried out to establish how piranha have moved to such distant corners of the world from their original habitat. It is anticipated that rogue exotic fish traders have released them in the lake to avoid being caught by anti-poaching forces.Description
Piranhas are normally about 15 to 25 cm long (6 to 10 inches), although some specimens have been reported to be up to 43 cm (18.0 inches) in length.
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 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. In the scale-eating Catoprion, the shape of their teeth is markedly different and the premaxillary teeth are in two rows, as in most other serrasalmines.Ecology
Piranhas are important ecological components of their native environments. Although largely restricted to lowland drainages, these fish are widespread and inhabit diverse habitats within both lotic and lentic environments. Some piranha species are abundant locally, and multiple species often occur together.As both predators and scavengers, piranhas influence the local distribution and composition of fish assemblages.Certain piranha species consume large quantities of seeds, but unlike the related Colossoma and Piaractus, herbivorous piranhas thoroughly masticate and entirely devour all seeds eaten and consequently do not function as dispersers.
Piranha have a reputation as a fearless fish who hunt their prey in ferocious packs. However, recent research, which "started off with the premise that they school as a means of cooperative hunting", discovered that they were in fact rather fearful fish, like other fish, who schooled for protection from their predators, such as cormorants, caimans and dolphins. Piranhas are "basically like regular fish with large teeth".
Research on the species Serrasalmus aff. brandtii and Pygocentrus nattereri in Viana Lake, which is formed during the wet season when the Rio Pindare (a tributary of the Rio Mearim) floods, has shown that these species eat vegetable matter at some stages in their life; they are not strictly carnivorous fish.Myths
There are various myths about piranhas such as how they can dilacerate a human body or cattle in seconds. These myths refer specifically to Pygocentrus nattereri, the red piranha.A recurrent myth is that they can be attracted by blood and are exclusive carnivores.A Brazillian 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.These myths were dismissed through research by Helder Queiroz and Anne Magurran and published on Biology Letters.
Relationship with humans
Piranha teeth are often used to make tools and weapons by the indigeneous population. Piranha are also popular as food, although if an individual piranha is caught on a hook or line, it may be attacked by other (free) piranhas.
Piranha are commonly consumed by subsistence fishermen and often sold for food in local markets.In recent decades, dried specimens have been marketed as tourist souvenirs.Piranhas occasionally bite and sometimes injure bathers and swimmers.A piranha bite is sometimes considered more an act of carelessness than that of misfortune, but piranhas are a considerable nuisance to commercial and sport fishers because they steal bait, mutilate catch, damage nets and other gear and may bite when handled.
Several piranha species appear in the aquarium trade.Piranhas can be bought as pets in some areas, but they are illegal in many parts of the United States including Alabama, Arizona, Arkansas, California, Colorado, Florida, Georgia, Hawaii, Kentucky, Louisiana, Maine, Massachusetts, Mississippi, Nevada, New Mexico, New York, North Carolina, Oklahoma, South Carolina, Texas, Utah, Virginia and Washington.
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. If underfed, piranhas are likely to become cannibalistic on others in their group.Theodore Roosevelt's description
There exists a legend that piranhas will skin and eat a human being alive, which is said to have been started with American President Theodore Roosevelt's visit to Brazil, and a spectacle set up by Brazilian fishermen. To guarantee a good show for the adventure-loving Roosevelt, local fishermen blocked off a portion of an Amazon tributary with nets and dumped hordes of starving piranhas into it when the U.S. president explored the region on a hunting trip. Then they sliced up a cow and tossed it in the river, setting off a wild feeding frenzy that quickly reduced the carcass to bones the "instant skeleton" now associated with piranhas. Roosevelt presented piranhas as vicious creatures in his 1914 book Through the Brazilian Wilderness, indicating that
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 they are found. If cattle are driven into, or of their own accord enter, the water, they are commonly not molested; but if by chance some unusually big or ferocious specimen of these fearsome fishes does bite an animal taking off part of an ear, or perhaps of a teat from the udder of a cow the blood brings up every member of the ravenous throng which is anywhere near, and unless the attacked animal can immediately make its escape from the water it is devoured alive.