Petrocephalus odzalaensis

General description: 

Petrocephalus odzalaensis is a medium sized species within the genus (maximum standard length observed = 99.3 mm; holotype = 92.9 mm). Body ovoid, body 2.6-2.9 longer than high (holotype = 2.6) and laterally compressed. Head length between 3.7 and 4.0 times in standard length (average = 3.9, holotype = 4.0). Snout short and round. Mouth small (4.0 ≤ Head length/mouth width ≤ 4.8, average = 4.3, holotype = 4.3), sub–terminal, opening just under the anterior half of the eye. Teeth small and bicuspid, 8–12 in a single row in the upper jaw (median = 11, holotype = 11), 18–23 in a single row in the lower jaw (median = 20, holotype = 18). Dorsal and anal fins originate in the posterior half of the body (1.5 ≤ standard length/pre–dorsal distance ≤ 1.6 and 1.6 ≤ standard length/pre–anal distance ≤ 1.7, respectively). Pre–dorsal distance slightly greater than the pre–anal distance. Dorsal fin with 20–22 branched rays (median = 21, holotype = 22). Anal fin with 27–29 branched rays (median = 28, holotype = 29). Scales cover the body, except for the head. Lateral line visible and complete with 36–38 (holotype = 38) pored scales along its length. Ten to 14 scales (average = 12, holotype = 11) between the anterior base of the anal fin and the lateral line. Caudal peduncle thin (1.9 ≤ Caudal peduncle length/caudal peduncle distance ≤ 2.3, average = 2.1, holotype = 2.1). Twelve scales around the caudal peduncle. Skin on head thick, turning opaque with formalin fixation. Knollenorgans clustered into the three distinct “rosettes” of Harder (1968).

Body background color pinkish–gray, darker dorsally. Pigmentation pattern consisting of three characteristic black patches: (1) a distinct ovoid black mark below the anterior base of the dorsal fin; (2) a small black mark at the base of the pectoral fin; and (3) an ovoid black mark centered at the base of the caudal fin, which does not extend on the upper and lower lobes. Fins translucent.

Diagnostic description: 

Petrocephalus odzalaensis is distinguished from all other Petrocephalus species in Central Africa by the following combination of characteristics. Dorsal fin shorter than anal fin. Dorsal fin with a maximum of 22 branched rays (range = 20–22). Anal fin with a minimum of 27 branched rays (range = 27–29). Mouth sub–terminal; ratio between head length and mouth position is between 4.2 and 5.0. Eye small (3.7 ≤ head length/eye diameter ≤ 4.2). Body pinkish–gray, darker dorsally, with the presence of three distinct pigmentation patches: (1) a distinct ovoid black mark situated below the anterior base of the dorsal fin on each side of the body; (2) a small black mark at the base of each pectoral fin; (3) an ovoid black mark on each side that is centered at the base of the caudal fin, not extending onto the upper and lower lobes of this fin. EOD of normal polarity, appearing triphasic at low gain, with two main phases and a small third phase. A final, fourth phase may be present, but it is always extremely small (< 1.5% of total peak–peak amplitude).


The EOD waveform is typical for the genus, similar to EODs produced by many other Petrocephalus species. The total EOD duration ranges from 0.231 to 0.339 msec, based on 1.5% voltage deviations from baseline relative to peak-peak amplitude. No EOD sex differences are apparent in the specimens recorded thus far.

Histological examination confirms that electrocytes are type NPp


To 99.3 mm SL


Petrocephalus odzalaensis forms a monophyletic group with Petrocephalus binotatus and Petrocephalus balayi.


Endemic to the central Congo basin.

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