Petrocephalus valentini is a small sized species within the genus (maximum standard length = 77.2 mm, holotype). Body ovoid, body 2.8 to 3.0 longer than high and laterally compressed. Head length between 3.4 and 3.7 times in standard length (paratype average = 3.6, holotype = 3.4). Snout short and round. Mouth small (4.7 ≤ Head length/mouth width ≤ 5.8) and sub–terminal, positioned under the anterior half of the eye. Eye large (2.9 ≤ Head length/Eye diameter ≤ 3.2). Teeth small and bicuspid, 7–12 (median = 9) in a single row in the upper jaw, 15–17 (median = 16) in the lower jaw. Dorsal and anal fins originate in the posterior half of the body (1.6 ≤ standard length /Pre–dorsal distance ≤ 1.7 and standard length / Pre–anal distance = 1.6). Pre–dorsal distance approximately equal to the pre–anal distance. Dorsal fin with 19–24 branched rays (median = 22). Anal fin with 24–26 branched rays (median = 25). Scales cover the body, except for the head. Lateral line visible and complete with 35–36 pored scales along its length. Nine to 12 scales (median = 11) between the anterior base of the anal fin and the lateral line. Caudal peduncle relatively thin (2.2 ≤ Caudal peduncle length/ Caudal peduncle depth ≤ 2.5, paratype average = 2.3, holotype = 2.3). Twelve scales around the caudal peduncle. Skin on head thick, turning opaque with formalin fixation. Knollenorgans clearly organized into two visible rosettes (the Augenrosette and the Nackenrosette). The third rosette, the Kehlrosette, is also present but this structure is not as visible as it is in other species (e.g., Petrocephalus binotatus).
Body uniformly white–silver, with two faint black patches, sometimes hardly distinguishable: (1) a dorsal mark on each side of the body, below the anterior base of the dorsal fin under the second to the sixth rays; (2) an ovoid/crescent–shaped mark centered at the base of the caudal fin (sometimes the center of this second mark is less distinguishable than two arms of the crescent, each 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.
Petrocephalus valentini is distinguished from all other Petrocephalus species in Central Africa (i.e., Lower Guinea and Congo provinces) by the following combination of characteristics. Dorsal fin with 19–24 branched rays. Anal fin with 24–26 branched rays. Eye large (Head lengt/eye diameter ≤ 3.2, range = 2.9–3.2). Mouth very small (Head length/Mouth width ≤ 5.8, range = 4.7–5.8). Twelve teeth or fewer in the upper jaw (range = 7–12), 17 teeth or fewer in the lower jaw (range = 15–17). Pigmentation pattern subtle, including two components: (1) a 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. EOD of normal polarity.
The EOD waveform produced by P. valentini n. sp. is similar in its characteristics to those produced by many other Petrocephalus species (mainly biphasic). EOD duration = 0.520 – 1.022 msec.
Electrocytes are assumed to be of type NPp based on the EOD waveform, although this has not been confirmed histologically.
To 77.2 mm SL
P. valentini belongs to a large clade of mostly Central Africa endemic species of Petrocephalus.
Apparently endemic to the central Congo basin. Common in Odzala National Park.
Elsewhere in the Congo basin, P. valentini n. sp. has been collected from the Lower Congo River in the vicinity of the Pool Malebo and Yangambi region.