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 in Wisconsin, although they typically do not survive cold winters. 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 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. 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. 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 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". 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. 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 other (free) piranhas. Piranhas 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 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. 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. Piranhas are likely to become cannibalistic on others in their group if underfed. 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-bellied piranha. A recurrent myth is that they can be attracted by blood and are exclusive carnivores. 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. These myths were dismissed through research by Helder Queiroz and Anne Magurran and published on Biology Letters. Nevertheless, a study in Suriname found that piranhas may occasionally attack humans, particularly when water levels are low. Attacks on humans are usually reported around docks where fish are frequently gutted, and entrails  are commonly thrown into the water. Hollywood would later emblazon the above gory image for posterity and profit. An example of this perception of piranhas in media appears in the 1967 James Bond film You Only Live Twice, where a piece of meat is shown being fed to pet piranhas owned by the film's main antagonist, Blofeld, then only a bone is raised from the water. Later on, a woman is thrown to the piranha pool, although all that is seen is water bubbling vigorously. Piranha (1978) and Piranha II: The Spawning (1981) perpetuated the piranha's sinister image by showing murderous piranha fish biting and eating humans. A 2010 remake titled Piranha 3D continued the trend and a sequel, Piranha 3DD, is in the making. |
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AN - Friday, March 9, 2012
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