Serrasalmus niger
Serrasalmus rhombeus (Redeye Piranha, and see below), is a fish of the piranha family Characidae found in South America in the Amazon and Orinoco river basins, the north and eastern Guiana Shield rivers, and northeastern Brazilian coastal rivers. Its length is up to 41.5 cm.
These piranhas live in very diverse habitats ranging from soft blackwater, to hard whitewater areas in the Amazon, and as such, are very tolerant of differing water chemistry.
Read more about Redeye Piranha: Names, In The Aquarium