Diagnosis: Nannocharax usongo is distinguished from all other described Nannocharax species by its very small distance between the posterior border of the anus and the articulation of first anal-fin ray (0.9–1.9 vs. 2.2–14.2% of standard length), its body coloration, which consist of 7–11 mostly big blotches along the lateral line often coalesced to one wide black band, and 7–12 small blotches along the dorsum (Ref. 80507).

Description: Body elongate, sides slightly compressed, greatest body depth at anterior dorsal-fin region; predorsal body profile slightly convex to snout; body profile at base of dorsal fin slightly posteroventrally sloped; dorsal body profile posterior to dorsal fin convex to adipose fin, from there straight to caudal peduncle; ventral body profile straight or very slightly posterodorsally sloped from tip of lower jaw to base of pectoral-fin and from pectoral fin insertion nearly straight to insertion of anal fin; body profile at base of anal-fin base slightly posterodorsally inclined; ventral body profile posterior to anal fin slightly posterodorsally sloped to caudal peduncle (Ref. 80507). Eyes large and situated closer to the tip of the snout than to the posterior end of operculum; eye diameter always smaller than interorbital width (Ref. 80507). Mouth small and subterminal (Ref. 80507). Upper jaw with a single row of 8-10 bicuspid, acute teeth; upper jaw teeth limited to the premaxilla (Ref. 80507). Body covered with ctenoid scales; lateral line complete and originating midlaterally behind operculum; two or three lateral line scales extending of on caudal fin (Ref. 80507).