Petrocephalus mbossou Lavoué, Sullivan & Arnegard, 2010
Original Published Description:
Petrocephalus mbossou is a large–sized species within the genus Petrocephalus (standard length = 127.1 mm). Body ovoid, longer than high (standard length /height = 3.0) and laterally compressed. Head length 3.4 times in standard length. Eye large (Head length/eye diameter = 3.7). Snout short and round. Mouth small (Head length/mouth width = 4.7), opening ventrally under the posterior half of the eye. Teeth small and bicuspid, 12 in a single row in the upper jaw, 14 in a single row in the lower jaw. Both the dorsal and anal fins originate in the posterior half of the body (standard length/pre–dorsal distance = 1.7 and standard length/pre–anal distance = 1.6, respectively). The pre–dorsal distance is slightly greater than the pre–anal distance. Dorsal fin with 24 branched rays. Anal fin with 26 branched rays. Scales cover the body, except for the head. Lateral line visible and complete with 37 pored scales along its length. Caudal peduncle relatively thin (caudal peduncle length/caudal peduncle diameter = 2.9) with twelve circumpeduncular scales. Skin on head thick, turning opaque with formalin fixation and containing numerous Knollenorgan electroreceptors organized into only two rosettes (the Nackenrosette and the Kehlrosette). The Augenrosette appears to be absent.
Body mostly white–silver. Dorsum slightly darker than the rest of the body. Pigmentation pattern consists of two distinct black markings: (1) a black patch of irregular shape below the anterior base of the dorsal fin (first ray to the sixth or seventh ray); (2) an irregularly-shaped mark centered at the base of the caudal fin that does not extend onto the rayed portions of the upper and lower caudal fin lobes. The fins themselves are translucent.
Petrocephalus mbossou is distinguished from all other Petrocephalus species in Central Africa by the following combination of characteristics. Dorsal fin with 24 branched rays. Anal fin with 26 branched rays. Mouth inferior and small (Head length/mouth width = 4.7) with 12 teeth in a single row in the upper jaw and 14 teeth in a single row in the lower jaw. Distance from the anterior extremity of the snout to the corner of the mouth only 2.8 times in head length. Weak pigmentation pattern with the presence of two black markings on each side of the body: (1) an irregular patch below the anterior base of the dorsal fin (first ray to the sixth/seventh rays); (2) an irregularly-shaped mark centered at the base of the caudal fin that does not extend onto the rayed portions of the upper and lower caudal fin lobes.
EOD of normal polarity (i.e., first major phase head–positive) and very brief duration. Unlike any other Petrocephalus species, the second head–positive phase in the EOD (P3) is larger in amplitude than the first head positive phase (P1).
Electric Organ Discharge
EOD recordings are only available for a single individual (the holotype). In this single individual of P. mbossou, EOD duration is very brief (0.144 msec), and the peak spectral frequency is unusually high (22.11 kHz), compared to other Petrocephalus species. In fact, duration and peak spectral frequency of this EOD recording fall outside the range observed for all other Petrocephalus. Like EODs of P. christyi, the EOD of the holotype of P. mbossou possesses a prominent head–negative, fourth peak (P4), the amplitude of which is 5.7% of the waveform’s total peak–to–peak swing. However, unlike the EOD of P. christyi (as well those of all other Petrocephalus species), the second head–positive peak (P3) is larger than the first head–positive peak (P1). Electrocyte anatomy is presumed to be of type "NPp" based on the EOD waveform.
To 127.1 mm SL
Ecology and Distribution
Endemic to the central Congo River basin
Evolution and Systematics
Petrocephalus mbossou and Petrocephalus christyi form a monophyletic group.
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