A piranha, or piraña, is a freshwater fish that lives primarily in the warm rivers of South America, especially in the Amazonian waters. The word piranha comes from an indigenous South American language, the Tapi-Guarani. The word piranha 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 piranha's teeth in makeshift weapons and tools.

A piranha is a fairly small fish, averaging eight inches (17cm) long, although larger specimens have been found. The largest species, a five-kgm piranha that lives in the Suriname/French Guiana, is actually herbivore. As is it well-known by 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 piranhas have been known to attack anything that goes into the water.

Piranha fish can make good aquarium pets if you're willing to put the time and effort into recreating the proper environment. They also require a large tank (at least 50 liters) to prosper, so you should also consider the added expense. Piranha 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 in general leads to fighting, and piranha fish have been known to band in groups, which is why 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 types of piranhas, the most popular pet piranha is the red-bellied piranha or Pygocentrus nattereri. Despite its name, the Red Bellied Piranha can be a variety of colors, from yellow to silver to black. Piranhas are illegal in many states, so make sure you check local regulations before you make a final decision.