Petrocephalus sauvagii is distinguished from all other Petrocephalus species in Central Africa by the following combination of characteristics. Very wide mouth (Head length/mouth wide ≤ 3.7, range = 2.7–3.7) associated with a characteristic head shape when viewed from below. Twenty–four to 30 teeth in the upper jaw and 30–34 in the lower jaw. Anal fin with at least 32 branched rays (range = 32–38). Dorsal fin with at least 25 branched rays (range = 25–30). Mouth sub–terminal; ratio between the head length and the mouth position as large as 7.4 (range = 5.5–7.4). Pigmentation pattern with two melanin markings, sometimes of weak intensity or even scarcely visible: (1) an irregularly round black mark below the anterior base (first to fourth rays) of the dorsal fin; (2) an ovoid blackish mark, often irregularly–shaped, at the base of the caudal fin, extending onto the upper and lower fleshy lobes of the fin. EOD of normal polarity, with two main phases followed by a third, smaller phase.
Petrocephalus sauvagii does not seem to make large school.