The Piranha

Jan 08, 2017 Features / Columnists, Interesting Creatures in Guyana

The piranha 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.
Piranhas belong to the subfamily Serrasalminae, which also includes closely related herbivorous fish including pacus. Traditionally, only the four genera Pristobrycon, Pygocentrus, Pygopristis and Serrasalmus are considered to be true piranhas, due to their specialised teeth.
The total number of piranha species is unknown and new species continue to be described. In 1988, it was stated that fewer than 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.
Piranhas are found only in the Amazon basin, in the Orinoco, in rivers of the Guianas, in the Paraguay-Paraná, and in the São 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.
However, piranha (inevitably former aquarium-dwellers) have been introduced into parts of the United States, even being occasionally found in the Potomac River, although they typically do not survive the cold winters of that region. Piranhas have also been discovered in the Kaptai Lake in south-east Bangladesh. Research is being carried out to establish how piranhas 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.
Piranhas are normally about 15 to 25 centimetres (cm) long (6 to 10 inches), although reportedly individuals have been found up to 43 cm (18.0 inches) in length.
Serrasalmus, Pristobrycon, Pygocentrus and Pygopristis are most easily recognised 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.
Ecologically, piranhas are important 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.
Piranhas 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”.
People are known to use piranha teeth to make tools and weapons and this fish species is also a popular food, although if an individual piranha is caught on a hook or line, it may be attacked by other (free) piranhas.
They 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. (Source: Wikipedia)

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The Piranha

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