Petrocephalus mbossou, Lavoué, Sébastien, Sullivan, John P. & Arnegard, Matthew E., 2010

Lavoué, Sébastien, Sullivan, John P. & Arnegard, Matthew E., 2010, African weakly electric fishes of the genus Petrocephalus (Osteoglossomorpha: Mormyridae) of Odzala National Park, Republic of the Congo (Lékoli River, Congo River basin) with description of five new species, Zootaxa 2600, pp. 1-52 : 38-41

Petrocephalus mbossou n. sp.

[Odzala field identification and in Lavoué et al. (2008): Petrocephalus sp. 11, OTU 11]

Images. Fig. 13 A, photo of the live holotype (CU 92389) and Fig. 13 B, photo of the preserved holotype.

Type material. Holotype, CU 92389 (morpho, EOD, DNA), sex undet., 127.2 mm SL. Republic of the Congo, Cuvette-Ouest, Lékoli River ( Congo basin), small branch of the Lékoli River, only ca. 300 meters long before it re-enters into the main channel of the Lékoli (0.62° N, 14.91° E), M.E. Arnegard, V. Mbossi, E. Kinzonzi, S. Lavoué, V. Mamonekene & P.B. McIntyre coll., June 2006.

Diagnosis. Petrocephalus mbossou n. sp. 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 (HL/MW = 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 (i.e., MP) 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 headpositive phase in the EOD (P3) is larger in amplitude than the first head positive phase (P1).

Description. This description is based on data collected solely from the holotype, which is the only specimen of this species collected to date. Table 10 provides morphometric ratios and meristic data for the holotype. Petrocephalus mbossou n. sp. is a large-sized species within the genus Petrocephalus (SL = 127.1 mm). Body ovoid, longer than high (SL/H = 3.0) and laterally compressed. Head length 3.4 times in standard length. Eye large (HL/ED = 3.7). Snout short (HL/SNL = 5.4) and round. Mouth small (HL/MW = 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 (SL/PDD = 1.7 and SL/PAD = 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 (CPL/CPD = 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.

Live coloration ( Fig. 13 A). 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.

Distribution ( Fig. 1 ). Endemic to the Congo River basin. The single known specimen of this species was collected in a fish trap, which we had baited with worms and set at night in the main channel of the Lékoli River on the last day of our second trip.

Electric organ discharge ( Fig. 13 C). EOD recordings are only available for a single individual (the holotype), so the following description of EOD features is in need of elaboration based on additional recordings. In this single individual of P. m b o s s o u n. sp., 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 individuals/species recorded in Odzala National Park ( Lavoué et al., 2008). Like EODs of P. christyi , the EOD of the holotype of P. mbossou n. sp. 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 from Odzala), 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.

Etymology. The specific epithet is the name given to Petrocephalus locally in the Lingala language. Speakers of Lingala recognize Petrocephalus as a natural group, which they call " mbossou ."

Remarks. We opted to describe P. m b o s s o u as a new species based only on the holotype for the following reasons. This individual specimen has a unique cytb haplotype and does not belong to any putative species (consisting of two or more specimens) of Petrocephalus in our molecular phylogenetic tree, and its body form and EOD are outside the ranges observed for all other Odzala Petrocephalus specimens, as well as all type material for Petrocephalus species of the Congo and Lower Guinea provinces. In taxonomic investigations of fish faunas from more accessible regions of Africa, it is normally (and reasonably) expected that investigators collect multiple specimens before describing a new species. However, given the remote location of Odzala National Park it may be some time before additional specimens become available. This fact and this species’ distinctive morphology, EODs and DNA justify describing P. mbossou n. sp. at this time with only a single specimen.

Figures

FIGURE 1. Map of Africa (right) showing the entire Congo River and its main tributaries together with the neighboring Lower Guinea province (first inset at center). The boundary between the Congo and Lower Guinea provinces is shown by a dashed line. Filled black circles indicate type localities for all Petrocephalus species that were described from either province and were considered valid just prior to the present study. Exact type localities are unknown for P. b a l a y i and P. sauvagii. Based on our understanding of the chronology of Central African exploration at the time of the descriptions, we estimate these type localities to be the following: the vicinity of Pool Malebo on the Lower Congo River near the modern cities of Brazzaville and Kinshasa [4.25 ° S, 15.29 ° E] for P. sauvagii; and the vicinity of the present-day city Lambaréné on the Lower Ogooué River [0.7 ° S, 10.22 ° E] for P. b a l a y i. Second inset at the far left: detailed map of Odzala National Park, located in the Congo River basin. Within the boundaries of the park, forest is shown in green and savannah in yellow. The red oval indicates our collection area (a segment of the Lékoli drainage system, including the lower parts of two of its tributaries, the Pandaka and Lékénie Rivers).

FIGURE 13. Petrocephalus mbossou n. sp. of the Lékoli River system of Odzala National Park, Republic of the Congo. A. Live photograph of the holotype (CU 92389; no scale). B. Photograph of the preserved holotype (scale bar = 1.0 cm). C. EOD waveform of the holotype. One EOD was arbitrarily selected from all recordings made of this individual. The selected EOD is shown here head-positive up (scale bar = 0.2 msec).