Much like other members of Deuterodon, and like some species in related genera, D. oyakawai is a small, silvery fish with fins in some combination of red and clear.

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

Before its nomination, instances of D. oyakawai were likely cataloged as congener D. heterostomus, specifically in the Ribeira de Iguape river basin.

Oyakawa is also notable for his major contributions to the knowledge of the fishes that inhabit the Ribeira de Iguape river basin.

[11] Deuterodon oyakawai is known to inhabit the Ribeira de Iguape river basin, which lies in southeastern Brazil.

Scales of varying types (ctenoid and cycloid) have been found in the stomach contents of examined specimens, which indicates differing sources of food rather than preferential treatment.

[6] However, it is a widespread and hardy species, and much of its native range is already protected; large swathes of the Atlantic Forest are preserved as national parks.