Crenuchus

Crenuchus spilurus, the sailfin tetra, is a species belonging to the South American darter family, Crenuchidae. It is found in the Amazon and Orinoco Basins, as well as various river Basins in the Guianas. It is the only member of its genus.

Ecology and Behavior of the Sailfin Tetra
The sailfin tetra, as a tiny species, is unlikely to participate in active dispersal across long distances. This is clear from the lack of people in the main channel of huge rivers. 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. As a hard substrate spawner with larvae that sink to the substrate, passive larval dispersal is reduced, implying a preference for philopatry. 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.