Diagnosis: Petrocephalus valentini is distinguished from all other Petrocephalus species in Central Africa by the following combination of characteristics: dorsal fin with 19-24 branched rays; anal fin with 24-26 branched rays; eye large, the ratio head length and eye-diameter between 2.9 and 3.2; mouth very small, the ratio head length and mouth width between 4.7 and 5.8; 12 teeth or fewer in the upper jaw; and 17 teeth or fewer in the lower jaw (Ref. 85331). Pigmentation pattern subtle, including two components: (1) a pale dorsal black mark on each side of the body below the anterior base of the dorsal fin, under the second to sixth dorsal rays; (2) an ovoid mark, sometimes scarcely visible, at the base of the caudal fin, extending weakly onto the upper and lower lobes of the fin (Ref. 85331).

Description: Body ovoid, longer than high, the ratio standard length and height between 2.8 and 3.0, and laterally compressed (Ref. 85331). Head length between 3.4 and 3.7 times in standard length (Ref. 85331). Snout short, the ration head length and snout length between 6.5 and 8.2, and round (Ref. 85331). Mouth small, the ration head length and mouth width between 4.7 and 5.8, and subterminal, positioned under the anterior half of the eye (Ref. 85331). Eye large, the ratio head length and eye-diameter between 2.9 and 3.2 (Ref. 85331). Teeth small and bicuspid, 7-12 in a single row in the upper jaw, 15-17 in the lower jaw (Ref. 85331). Caudal peduncle relatively thin, the ration caudal peduncle length and caudal peduncle height between 2.2 and 2.5 (Ref. 85331). Dorsal and anal fins originate in the posterior half of the body; pre-dorsal distance approximately equal to the pre-anal distance; dorsal fin with 19-24 branched rays; anal fin with 24-26 branched rays (Ref. 85331). Scales cover the body, except for the head; lateral line visible and complete with 35-36 pored scales along its length; 9-12 scales between the anterior base of the anal fin and the lateral line; 12 scales around the caudal peduncle (Ref. 85331). Skin on head thick, turning opaque with formalin fixation; knollenorgans clearly organized into two visible rosettes (Ref. 85331).

Colouration: Body uniformly white-silver, with two faint black patches, sometimes hardly distinguishable: a dorsal mark on each side of the body, below the anterior base of the dorsal fin under the second to the sixth rays; an ovoid/crescent-shaped mark centered at the base of the caudal fin , with each arm slightly extending onto the upper and lower parts of the caudal fin; there is no melanin marking at the base of the pectoral fins; fins translucent (Ref. 85331).