Petrocephalus simus Sauvage 1879

From Lavoué et al (2004): Body ovoid, longer than high (2.6 < standard length/body height < 3.4) and compressed. Head length between 3.4 and 4.3 times in standard length. Snout short and round. Mouth relatively narrow (4.1 < head length/mouth width < 6.1), sub-terminal, just under the anterior half of the eye. Teeth small and bicuspid, 8 to 14 in a single row in the upper jaw, 16 to 22 in the lower jaw. Dorsal fin originates in the posterior half of the body (1.5 < standard length / pre-dorsal distance < 1.8). Pre-dorsal distance equal to, or slightly greater than, the pre-anal distance. Scales cover the body, except for the head. Lateral line visible and complete with 36 to 44 pored scales along its length. Caudal peduncle relatively thin (2.0< Caudal peduncle length / Caudal peduncle depth < 3.7, average 2.8). Twelve scales around the caudal peduncle. Skin on head thick, with numerous electroreceptors. Skin turns opaque with formalin fixation. Three rosettes of Knollenorgan electroreceptors are present on the head: the “Nakenrosette” behind the eye and dorsal to the opercular flap, the “Kehlrosette” anterior to the pectoral fin, and the “Augenrosette” anterior and slightly dorsal to the eye.

Body silver, slightly darker dorsally including the head. Sub-dorsal round black spot never present on the side, as some authors have mentioned previously. Fins translucent, except for the first rays of the dorsal fin, which appear black. Moreover, the first external rays of the caudal fin are pigmented black, in a crescent shape centred on the base of the caudal fin.