Petrocephalus pulsivertens

General description: 

Petrocephalus pulsivertens is a relatively large sized species within the genus Petrocephalus (maximum standard length = 114.8 mm, the length of the holotype). Body ovoid, body 2.6-2.9 longer than high (holotype = 2.8) and laterally compressed. Head length between 3.6 and 3.7 times in standard length (holotype = 3.7). Eye large (3.2 ≤ head length/eye diameter ≤ 3.5, average = 3.4, holotype = 3.5). Snout short and round. Mouth large (3.0 ≤ head length/mouth width ≤ 3.7, average = 3.3, holotype = 3.0), sub–terminal, opening just under the anterior half of the eye. Teeth bicuspid, small and numerous, 15–21 (average = 18, holotype = 21) in a single row in the upper jaw, 24–30 (average = 28, holotype = 29) in a single row 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 1.7 ≤ standard length/pre–anal distance ≤ 1.8, respectively). Pre–dorsal distance equal to, or slightly greater than, pre–anal distance. Dorsal fin with 25–27 branched rays (median = 26, holotype = 26). Anal fin with 31–35 branched rays (median = 33, holotype = 34). Scales cover the body, except for the head. Lateral line visible and complete with 38–40 pored scales along its length. Caudal peduncle relatively thin (2.1 ≤ Caudal peduncle length/Caudal peduncle distance ≤ 2.3, holotype = 2.2). Twelve scales around the caudal peduncle. Skin on head thick, becoming opaque with formalin fixation. Knollenorgan electroreceptors on head clustered into three distinct rosettes.

Body and head mostly whitish–silvery, but head also exhibits faint metallic blue–purple iridescence. Dorsum darker than the rest of the body. Melanin patterning consists of two distinct black marks: (1) a distinct ovoid melanin mark below the anterior base of the dorsal fin on each side of the body and (2) a crescent–like melanin mark, sometimes diffuse, centered at the base of the caudal fin on each side and extending onto the upper and lower parts of the caudal fin. No black mark is present at the base of the pectoral fins. The fins themselves are mostly translucent.

Diagnostic description: 

Petrocephalus pulsivertens is distinguished from all other Petrocephalus species in Central Africa by the following combination of characteristics. Dorsal fin with at least 25 branched rays (range = 25–27). Anal fin with at least 31 branched rays (range = 31–35). Mouth large (Head length/mouth width ≤ 3.7, range = 3.0–3.7). Fifteen to 21 teeth in the lower jaw; 24–30 teeth in the upper jaw. Eye large (Head length/eye diameter ≤ 3.5, range = 3.2–3.5). Pigmentation pattern consists of two distinctive melanin markings (black patches): (1) a distinct ovoid mark below the anterior base of the dorsal fin; and (2) a crescent–like mark, sometimes diffuse, centered at the base of the caudal fin and extending onto the upper and lower parts of the caudal fin.

EOD appears to be inverted in polarity, with a first main phase that is negative under the standard recording geometry, resulting in a waveform that is very distinctive in comparison to all known congeners.


The EOD waveform of Petrocephalus pulsivertens resembles an inverted–polarity version of the "typical" Petrocephalus EOD. That is, the temporal sequence of electrocyte face firing known for all other Petrocephalus (i.e., firing of the posterior electrocyte face preceding firing of the anterior electrocyte face) appears to be reversed in P. pulsivertens. At high gain, however, one can see that the very first event in the EOD is a minute head-positive deflection. This waveform feature is consistent with currents from the stalks of the posterior electrocyte face (and possibly from the early part of posterior face firing) slightly preceding anterior face firing.

Given its inverted–polarity appearance, the EOD of P. pulsivertens is immediately recognizable as distinct from those of all other congeners. Based on a threshold of 1.5% of peak-peak amplitude (and at ambient recording temperatures), the duration of the EOD of P. pulsivertens ranges from 0.270 to 0.418 msec, falling in the range of many "typical" Petrocephalus EODs.

Despite the waveform inversion, electrocytes of P. pulsivertens are known to be of type "NPp", the character state also shared by all other Petrocephalus species investigated to date.


To 114.8 mm SL


Petrocephalus pulsivertens belongs to a clade of Central African species of Petrocephalus.


Endemic to the Congo River basin where Petrocephalus pulsivertens occurs in Odzala (Republic of Congo), the vicinities of Brazzaville (i.e., the Pool Malebo), the Dja River (Cameroon) and the Dzangha–Sangha region (Sangha River basin, Central African Republic).


P. pulsivertens along the main course of the Lékoli River in Odzala. This species seemed to be absent from the small tributary creeks flowing through forest or savannah.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith