Crenuchus spilurus, the sailfin tetra, is a species belonging to the South American darter family, Crenuchidae.

Active migration in open areas, particularly in a predator-rich environment like the Amazon basin, presents unique obstacles for small, non-schooling fish.

The species makes specific use of the rhythmic oscillations of the dorsal fin to control its movements precisely, stressing its close relationship with complex structures.

Unlike most members of the Characiformes group, the sailfin tetra does not swim much and prefers to stay near stream margin structures.

This behavior stands in stark contrast to the majority of the order's species, which are either spread spawners or have minimal site selection for spawning.