They are a fish found in rivers with little water movement or in stagnant, warm water. They swim in large shoals and it is in groups when they can attack animals as big as an ox, generally wounded, which they detect thanks to their fine sense of smell. They feed on fish, seeds and fruits. They are called red piranhas because during the breeding season their belly turns a bright red colour. This is after the rains, in April and May. The eggs are laid in the vegetation at the bottom of the river and the couple defends them very aggressively.
Their teeth are so sharp and cut so much that the Guaycuru and the Abipones people used their jaws as knives or scissors.