Serrasalmus nattereri (non Günther, 1864)
The red-bellied piranha or red piranha (Pygocentrus nattereri) is a species of piranha native to South America, found in the Amazon River Basin, coastal rivers of northeastern Brazil, and the basins of the Paraguay and Paraná. The red-bellied piranha has a popular reputation as a ferocious predator, despite being primarily scavengers. 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). The way to distinguish males from females is that the female has a slightly deeper color of red on her belly.
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 up to 1000 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 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 
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. 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.
- "Animal Diversity Web: Pygocentrus nattereri". Animal Diversity Web. University of Michigan.
- "BBC Nature Red-bellied piranhas". BBC Nature Wildlife. BBC. Retrieved 10 December 2012.
- "Red Bellied Piranha (Serrasalmus nattereri)". Marwell Animal Encyclopedia. Marshwell Wildlife. Retrieved 24 January 2013.
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