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The red-bellied piranha (Pygocentrus nattereri) is a species of piranha. This species lives in the Amazon River Basin, coastal rivers of northeastern Brazil, and the basins of the Paraguay, Paraná and Essequibo Rivers. The red-bellied piranha has a reputation for being one of the most ferocious freshwater fish in the world.[weasel words] As their name suggests, red-bellied piranhas have a reddish tinge to the belly when fully grown, although juveniles are a silver colour with darker spots. They grow to a maximum length of 33 centimetres (13 in) and a weight of 3.5 kilograms (7.7 lb). This species is restricted in some locations. The red-bellied piranha has the narrowest intenstine of any bony fish.
Their diet consists largely of fish, insects, worms, crustaceans, and the occasional larger animal. In contrast to their popular reputation of feeding on live animals, red-bellied piranhas usually feed on dead, dying, and injured vertebrates in the wild, but have been known to attack healthy animals. The fish usually feed in large schools around dusk and dawn. They locate their prey by scent or motion using a set of sensors down the sides of their bodies, the lateral line system.
Red-bellied piranha usually spawn around April and May during the rainy season. The male will build a dug-out nest in rocks and vegetation, awaiting a female. Females can lay around 600 eggs which the male fertilizes. Males become extremely territorial during spawning, and will prevent other fish from approaching the nest. After the eggs hatch, both parents guard the broods. Red-bellied piranhas exhibit very little obvious sexual dimorphism, although females may have slightly more yellow on the belly than males.
Red-bellied piranha in media
Many myths surround this species. The 1978 film Piranha by Joe Dante shows these fish in a similar light to Jaws. Piranha was followed by a sequel, Piranha II: The Spawning, in 1981, and two remakes, one in 1995, and one in 2010. Films such as these, and stories of large schools of red-bellies attacking humans, fuels their exaggerated and erroneous reputation as being one of the most ferocious freshwater fish. In reality, they are generally timid scavengers, fulfilling a role similar to vultures on land. In the 2010 film Piranha 3D, Christopher Lloyd's character identifies a specimen of the fictional monstrous piranha, specifically as Pygocentrus nattereri, but erroneously refers to them as the first piranhas, when in reality, red-bellied piranha are most likely not the "original" species.
In an aquarium
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Red-bellied piranhas are sometimes kept as aquarium fish. Their natural diet consists of live prey and dead animals and fish. Live feedings to captive piranhas can introduce diseases, and goldfish contain a growth-inhibiting hormone which in turn will affect piranhas. They may be kept with certain armoured catfish, such as Hypostomus plecostomus, but this is generally discouraged amongst the piranha-keeping community. Red-bellied piranhas, particularly when juvenile, will sometimes bite one another in the aquarium, normally on the fins, in behaviour called 'fin nipping'. Fish that have had their fins nipped will grow them back surprisingly rapidly. Red-bellied piranhas are generally timid in the aquarium for a variety of reasons, i.e. due to unnaturally high light conditions, poor water quality, and lack of cover, which juvenile fish in particular need to hide. Some hobbyists have been disappointed with the fish's timidity in the aquarium, having acquirred them for their exaggerated reputations as killers. Piranhas require frequent water changes with soft water. Extensive filtration is required for these fish.