Petrocephalus sullivani is a species of medium size (maximal standard length observed = 104.7mm). Body ovoid, longer than high (2.8 < standard length / body height < 3.7), and compressed. Snout short and very round. Mouth inferior, below the eye. Teeth small and bicuspid, with 10 to 13 in the upper jaw and 12 to 15 in the lower jaw. Eye relatively large. Eye diameter between 3.0 and 4.1 times in head length (average 3.5). Dorsal fin originates in the posterior half of the body (1.5 < standard length / pre-dorsal distance < 1.7). Pre-dorsal distance equal to, or slightly greater than, pre-anal distance. Scales cover the entire body, except for the head. Lateral line visible and complete, with 35 to 42 pored scales along its length. Ratio of caudal peduncle length to height between 2.1 and 3.2 (average 2.5). Twelve circumpeduncular scales present. Thick skin, with numerous electroreceptors, covers the head and part of the body. Skin turns opaque with formalin fixation. Three rosettes of Knollenorgan electroreceptors present on the head: the “Nakenrosette”, the “Kehlrosette”, and the “Augenrosette”.
The body is silver to slightly gold. The back is darker than the abdomen. With differing angles of illumination, the golden metallic reflections are more prominent. The fins are unpigmented, with the exception of the first rays of the dorsal fin, which are black.
Twenty to 25 branched rays in the dorsal fin and 24 to 30 in the anal fin; 14 to 20 scales (average 17.5) between the anterior base of the anal fin and the lateral line; mouth clearly inferior (distance between anterior extremity of the snout and corner of the mouth between 2.7 and 4.4 times in head length; mouth opens under the posterior half of the eye; large eye (diameter of the eye between 3.0 and 4.1 times in head length, average 3.6); and no sub-dorsal black spot. The EOD is short (216 µs mean duration) with a peak FFT frequency of 9597 Hz. The EOD presents a prominent third phase (P3) with an amplitude of 12.8% of peak-to-peak height.
The EODs of Petrocephalus sullivani are short in duration with a high peak power spectrum frequency. The third phase (P3) is quite prominent in this species (12.8 ± 3.6 % of peak-to-peak height).
To 104.7 mm SL
Petrocephalus sullivani belongs to a large clade of endemic species of Central Africa
Petrocephalus sullivani has been collected from the Ogooué basin (excepting its most upper and lower reaches), the Ntem and Ivindo basins, and the Nyanga basin.