Its diet was not well-known until a 1970 study that classified it as a voracious lepidophage, preying on other fish species for their scales.

Most of its food is sourced from related fishes such as Psalidodon fasciatus, a cryptic species to which D. heterostomus bears a strong visual resemblance.

[3] It was known as such for most of its existence as a species, and can still be found listed under the genus Probolodus in some databases, such as GBIF[4] and the Encyclopedia of Life.

[6] This updated classification is reflected in databases including FishBase,[7] the World Register of Marine Species,[2] and Eschmeyer's Catalog of Fishes.

[11] Deuterodon heterostomus reaches a maximum of roughly 10 cm (3.9 in) SL (standard length, without the tail fin included).

There is another spot on the caudal peduncle that continues onto the fin-rays in younger specimens; the ray pigmentation fades somewhat in adults.

[16] Some larger males develop backwards-facing hooks on select rays of the pelvic fin when mature.