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The piranhas or pirañas are a group of carnivorous freshwater fish living in South American rivers. They belong to five genera of the subfamily of Serrasalminae (which also includes closely related herbivorous fish including pacus and silver dollars).


 


They are normally about 15 to 25 cm long (6 to 10 inches), although reportedly individuals have been found up to 40 cm in length. They are known for their sharp teeth (able to bite through a steel fishing hook) and an aggressive appetite for meat and flesh. They are normally only found in the Amazonian, Guianas and Paraguayan river systems. However, piranha (most likely former aquarium-dwellers) are also occasionally found in the Potomac River, but they typically do not survive the cold winters of that region


Recent research on Serrasalmus aff. brandtii and Pygocentrus nattereri in Viana Lake, which is formed during the wet season when the Rio Pindare (a left bank tributary of the Rio Mearim) floods, has shown that these species eat vegetable matter at some stages in their life history. They are not strictly carnivorous fishes.

Piranhas generally pose little threat to humans, and attacks on humans are extremely rare. Natives frequently swim in piranha infested water without attacks or scratches. However, it is not recommended to swim where piranha live in drought season because of increased aggressiveness caused by food scarcity and increased tendency to form large schools. Piranha fish also have the same sensory system that enables sharks to detect blood in minuscule amounts, so it is believed that swimming with an open cut may enhance the chance of an attack.

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 Kingdom: Animalia

 Phylum: Chordata

 Class: Actinopterygii

 Order: Characiformes

 Family: Characidae

 Subfamily: Serrasalminae