A piranha, or piraña, is a freshwater fish that lives primarily in the warm rivers of South America, especially in the Amazonian waters. The name comes from an indigenous South American language, the Tapi-Guarani. It seems to be a composite of two words: pira meaning fish, and sanha, which means tooth. Their fearsome reputation is well-earned: a piranha's teeth are so sharp that they can easily sever a human finger with just one bite. In fact, local indigenous tribes use the teeth in makeshift weapons and tools.
A fairly small fish, the piranha averages 8 inches (17 cm) long, although larger specimens have been found. The largest species, an 11 pound (5 kg) piranha that lives in the Suriname/French Guiana, is actually a herbivore. As is it well-known by most, most piranhas are carnivorous, feeding mainly on small fish, crustaceans, and carrion. Attacks on people are rare, though they do happen sometimes, especially if something like blood attracts them at first. This is especially true during the dry season, when food becomes scarce, and the fish have been known to attack anything that goes into the water.
Piranha fish can make good aquarium pets if owners are willing to put the time and effort into recreating the proper environment. They also require a large tank (at least 13 gallons (50 liters)) to prosper, so people should also consider the added expense. These fish are highly territorial, and they can turn cannibalistic if kept in a small space. They are also shy, so they need to be provided with plenty of hiding spaces. Overcrowding usually leads to fighting, and piranha fish have been known to band in groups, which is why it is a good idea to keep an even number of them in the tank.
When kept in a fish tank, a piranha can be fed shrimp, fish pieces, or basically any fish food available at pet stores. While there are many species, the most popular pet is the red-bellied piranha or Pygocentrus nattereri. Despite its name, this fish can be a variety of colors, from yellow to silver to black. Piranhas are illegal in many places, so people who want to keep them should check local regulations.