Petrocephalus sullivani is distinguished from all other Petrocephalus species from Gabon by the following characters: 20 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 extremityof th esnout and corner of the mouth between 2.7 and 4.4 times in head length; mouth opens under the posterior half of the eye, whereas in P. simus and P. balayi it opens under the anterior 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 ms 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. Eye relatively large. Eye diameter between 3.0 and 4.1 times in head length (average 3.5) (Ref. 52344).