As they mature their silvery body becomes less mottled and changes to a darker grey or black colour.

[1] The black piranha is found in northern South America, east of the Andes.

[4] The black piranha occurs in a wide variety of habitats but the adults have a preference for the larger, deeper river channels where they normally hunt for prey either in deep stretches or in the vicinity of rapids.

The juveniles are most frequently recorded in stiller stretches where there is thick submerged or marginal vegetation.

[7] The morphological differences between populations suggest that S. rhombeus is a species complex,[4] but molecular work to confirm this has yet to be undertaken.