Picture above is a redeye piranha Serrasalmus rhombeus. Redeye piranha is just one of the common names this fish goes by. Other more popular common names is White Piranha and Black Piranha.
The reason I used redeye piranha is because there is so much confusion between white and black piranha that the name is almost meaningless. If you do a search for either of these names you will be rewarded with hundreds of misidentified fish.
Why because there is even some division in the scientific community about these spesies, more research needs to be done and variablity in coloration and body shape is significant when you consider the local the fish was caught and the age of the fish. This is a young piranha identification is more straight foward when they get larger.