Petrocephalus grandoculis is distinguished from all other Petrocephalus species in Central Africa by the following combination of characteristics: very small mouth (mouth width 5,2-6,1 times in head length), 8-11 teeth in the upper jaw, lower jaw with 18-22 teeth, eye large (eye diameter 2,8-3,2 times in head length), snout short, dorsal fin with 24-26 branched rays, anal fin with 30-33 branched rays (Ref. 85331). Pigmentation pattern consists of two melanin markings (black patches): (1) a distinct, although generally weak, round black mark on each side of the body below the anterior base of the dorsal fin (first to fifth rays); and (2) a crescent-like mark at the base of the caudal fin on each side, not extending onto the rayed portions of the upper and lower caudal fin lobes (Ref. 85331).