[2] It can be distinguished from other species by: its body depth (26.7–34.8% of its standard length); its short and pointed snout smaller than the orbital diameter; and a reduced number of branched anal fin rays.

It possesses a single humeral spot that is constricted to the region above the lateral line; at the same time it shows a conspicuous midlateral body stripe from opercle to the caudal fin base, an autapomorphy of this precise species.

The species name is derived from the Greek pelekus, meaning "axe", referring to the pigmentation shape resulting from the adjoinment of the humeral spot with the midlateral stripe.

Its maxilla extends posteriorly to vertical through the anterior margin of the orbit, being aligned at an angle of about 45 degrees relative to the longitudinal body axis.

[3] In alcohol, the fish's dorsal and dorsolateral portion of the head and body are a dark brown colour.

The scales on its midlateral surface are bordered with dark brown chromatophores that form an overall reticulate pattern.

Along the upper edge of its opercle to the base of its middle caudal fin rays extends a black midlateral stripe.

[3] D. pelecus is known from the upper Rio Pardo, at Cândido Sales in the state of Bahia, eastern Brazil.

Deuterodon pelecus cohabitates this ecosystem with the spotfin hogfish, Apareiodon itapicuruensis, Geophagus brasiliensis, Parotocinclus cristatus, and Hoplias, Characidium and Astyanax species.