Piranha
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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 warm North American rivers and small lakes, but they typically do not survive long.[1] (http://www.washingtonpost.com/wp-dyn/content/article/2005/05/28/AR2005052801079_pf.html)
Recent research (http://www.practicalfishkeeping.co.uk/pfk/pages/item.php?news=695) 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.
The name piranha may come from a hybrid language composed of Tupi-Guarani languages; it may be a compound word made of the components 'pirá', meaning 'fish', and 'sanha' or 'ranha', meaning 'tooth'. In Tupi, inalienably possessed nouns take the prefix 't-', 's-', or 'r-' depending on the possessor, or zero in combination; thus 'pirá'+'anha'. Alternately, it may come from Tupi 'pirá' ('fish') and 'ánha' ('cut'). It is pronounced (in IPA) (or ), , or ).
In the Maroni River in Suriname/French Guiana a large kind, weighing up to five kilograms, can be found; it seems to be an herbivore. This species hosts colonies of worms in its stomach.
Alleged danger to humans
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. It is not recommended to swim where piranha live in drought season because of increased aggressiveness caused by food scarcity. Piranha fish do not have the same sensory system that enables sharks to detect blood in miniscule amounts, so it is not believed that swimming with an open cut would provoke an attack.Template:Fact
Stories about schools of piranhas turning horses or people into skeletons within seconds are the result of numerous re-tellings and exaggerations over the years. While piranha schools can reach over a thousand in count, and bites do happen, there are no documented reports of someone being killed in a piranha attack. There are, however, documented cases of people dying from other causes and then being consumed by piranha (they just happened to be the scavenger that got there first).