Hemigrammus durbinae can be diagnosed from most congeners, except H. marginatus, by lacking a conspicuous humeral spot and by having two dark patches of pigmentation on caudal-fin lobes. It differs from H. marginatus by having two conspicuous patches of dark pigmentation occupying most of the caudal-fin lobes, except the tips, which are hyaline (vs. relatively faint dark pigmentation along caudal-fin distal portion, tips of caudal fin dark) and by having two dark narrow stripes along anal-fin base, the first sub-parallel to anal-fin base, extending approximately along region where hypaxial musculature and the muscles of anal fin meet, and the second along anal-fin base (vs. only an inconspicuous dark stripe along anal-fin base present). Other characters useful to differentiate it from H. marginatus include the following: 5-8 pored lateral line scales (vs. 8-14); upper jaw length 32.1-41.6% in head length (vs. 42.3-46.0%); length of dorsal-fin base 9.9-13.1% of SL (vs.13.6-15.1% of SL); length of dorsal-fin length 22.7-27.1% of SL (vs. 27.6-32.6% of SL); and distance from eye to dorsal-fin origin 38.7-45.9% of SL (vs. 34.6-37.8% of SL) (Ref. 101340).

Description: Dorsal-fin rays ii,8 or 9; anal-fin rays iv,16, 17, 18, 19, 20, or 21; pectoral-fin rays i,9, 10, or 11; pelvic-fin rays i,6 or 7 (Ref. 101340).