While little research exists regarding its ecological habits, such as diet and mating practices, its environment preferences are known to include marshy lowlands, and it easily lives in sympatry with various other fish species in the Cauca and Magdalena river basins.

Congener Astyanax atratoensis has been noted to bear a strong visual resemblance to A. caucanus, and researchers as early as 1908 were commenting on a possible relationship.

[6] Based on modern understandings, this may not remain the case; recent research places A. atratoensis in the subgenus Poecilurichthys.

The reasoning behind this was not made clear in the nominal text, but modern etymologists suspect that the appearance of type species Astyanax argentatus may be responsible; its scales are large and silvery, perhaps comparable to armor or a shield.

When compared with congeners A. filiferus and A. magdalenae from the same subgenus, A. caucanus presents with a somewhat more generalized morphology, while the other two are more specialized for their environments.

[12] Astyanax caucanus was originally described from the Cauca River Basin in Colombia,[13] and is solely recorded from the country (located in the far northwest of South America).

[17] In aquatic macrophyte patches (multicellular plants, as opposed to algae) of the Ayapel Swamp Complex in Colombia, A. caucanus is one of a small handful of species that makes up a great deal of the biomass; other common species with which it coexists in the same region include Eigenmannia virescens, Roeboides dayi, Cyphocharax magdalenae, Triportheus magdalenae, Caquetaia kraussii, and Aequidens latifrons.

The IUCN considers A. caucanus a species of least concern due to a wide range and a lack of active threats.

A 2007 article from Colombian newspaper El Tiempo regarding the Cauca suggests pollution rates as high as 500 tons of residual waste per day.