The truth is that pirhanas is a name used for a number of fishes within the subfamily Serrasalminae and only a few of those are predators. Many pirhana species survives by eating veggies and other are specialized to only eat certain parts of fish such as eating fins. These species feed of other fish without killing them and bits of small fin pieces from a lot of different fish thereby leaving the prey fish virtually unharmed and the fin eventually grows back again.

There are however some small truth behind the myth of the killer Pirhana. The predatory species, those who have been the basis for the myth mainly eat fish but they do sometimes eat mammals during the dry season if the have in large numbers have been captured in small bodies of water where the food supply have been used up. They are under these conditions able to like the myth says tear the flesh from the bones in a matter of seconds, or more often in minutes. However during more normal conditions and during the wet seasons the pirhanas are spread over far greater areas in the flooded jungle and posses no life threatening threat to humans and other larger mammals.