Petrocephalus christyi is distinguished from all other Petrocephalus species in Central Africa by the following combination of characteristics. Dorsal fin with 22–24 branched rays. Anal fin with 25–29 branched rays. Eye large (Head length/eye diameter ≤ 4.2, range = 3.1–4.2). Mouth small (2.9 ≤ Head length /mouth width, range = 2.9–5.5). Nine to 13 teeth in the upper jaw, 17–22 teeth in the lower jaw. Melanin patterning consisting of two characteristic black patches: (1) a distinct round mark below the anterior base (first to the fifth rays) of the dorsal fin; (2) a somewhat diffuse crescent–like mark, centered at the base of the caudal fin and extending onto the fleshy dorsal and ventral lobes of this fin.
In the small number of individuals recorded so far, the EOD is of normal polarity, four–phasic, with a relatively slow initial rise.
EOD of this species does appear to be distinctive. The EOD exhibits normal polarity and is four–phasic with a large, negative–going P2 and smaller peaks, P1, P3 and P4. Similar to the EODs of the Odzala population of P. microphthalmus, a relatively long, slow rise occurs during the initial part of the first head–positive phase in the EODs of both individuals of P. christyi. This rise toward P1 has a shoulder-like inflection point, which at magnified gain is seen to possess a small, negative-going local peak. Both the slow rise and inflection point are subtle features of the EOD; they are only visible in amplified traces. Unlike the EODs of P. microphthalmus, however, those of the two P. christyi individuals possess a prominent head–negative fourth peak (P4), the amplitude of which is 4.5 – 8.6 % of the waveform’s total peak–to–peak swing. A prominent P4 is also present in the EOD emitted by the only individual of Petrocephalus mbossou ever recorded, but otherwise a P4 seems to be rare in Petrocephalus. Based on 1.5% voltage deviations from baseline relative to peak-peak amplitude and at ambient recording temperatures, duration of the EOD is between 0.284 and 0.390 msec in P. christyi, falling in the range of many other Petrocephalus species. Electrocyte anatomy is presumed to be of type NPp based on the EOD waveform, but this has not yet been confirmed histologically.
To 100.0 mm SL
Petrocephalus christyi is the sister group of P. mbossou nested within a large clade of mostly Central Africa endemic species.
Endemic to the Congo River basin. The type specimens were collected at the locality Bosabangui along the Lindi River. Petrocephalus christyi is known from several localities in the Congo basin: Odzala, Pool Malebo (Lower Congo), Yangambi region, etc.