Petrocephalus zakoni

description

Description. Morphometric ratios and meristic data are given in Table 2 for the holotype and paratypes separately. Petrocephalus zakoni n. sp. is a small sized species within the genus (maximum SL in the type series = 86.0 mm, maximum SL observed in all specimens = 90 mm). Body ovoid, longer than high (2.5 ≤ SL / H ≤ 2.8, paratype average = 2.6, holotype = 2.8) and laterally compressed. Head length between 3.4 and 3.7 times in standard length (paratype average = 3.6, holotype = 3.6). Eye large compared to many Petrocephalus species (3.1 ≤ HL / ED ≤ 3.3, paratype average = 3.2, holotype = 3.2). Snout short (6.1 ≤ HL / SNL ≤ 8.5, paratype average = 7.2, holotype = 6.2) and round. Mouth small (4.4 ≤ HL / MW ≤ 5.0, paratype average = 4.7, holotype = 4.5) and sub-terminal, opening under the posterior half of the eye. Teeth small and bicuspid, 6 – 10 (paratype median = 8, holotype = 9) in a single row in the upper jaw, 18 – 22 (paratype median = 19, holotype = 20) in the lower jaw. Dorsal and anal fins originate in the posterior half of the body (1.6 ≤ SL / PDD ≤ 1.7, paratype average and holotype = 1.6; 1.6 ≤ SL / PAD ≤ 1.7, paratype average and holotype = 1.6). Pre-dorsal distance roug

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

diagnosis

Diagnosis. Petrocephalus zakoni n. sp. is distinguished from all other Petrocephalus species in Central Africa (Lower Guinea and Congo provinces) by the following combination of characteristics. Dorsal fin with 23 or 24 branched rays. Anal fin with 27 or 28 branched rays. Eye large (HL / ED ≤ 3.3, range = 3.1 – 3.3). Mouth small (4.4 ≤ HL / MW, range = 4.4 – 5.0). Ten teeth or fewer (range = 6 – 10) in the upper jaw. Twentytwo teeth or fewer (range = 18 – 22) in the lower jaw. Unique pigmentation pattern consisting of three well defined black patches (Fig. 4 A): (1) an intense dark mark on each side of the body close to the anterior base of the dorsal fin, often extending onto the first dorsal rays, forming a characteristic saddle across the dorsum; (2) a mark on each side of the body at the base of the pectoral fin; (3) a crescent-shaped mark on each side of the body centered at the base of the caudal fin, extending onto the upper and lower parts of the caudal fin. EOD of normal polarity (i. e., first major phase head-positive).

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

discussion

Remarks. Given our identification of specimens from the Lower Congo River and the Dzangha-Sangha Reserve (Sangha River), Petrocephalus zakoni n. sp. is likely a common species in the Congo basin. This species has been previously misidentified as Petrocephalus christyi Boulenger, 1920 because its body proportions are similar to those of P. christyi. In addition, both species exhibit an intense sub-dorsal melanin marking on the flank. Nevertheless, these species can be distinguished by the presence of a black spot at the base of the pectoral fins in P. zakoni n. sp. (absent in P. christyi), the shape of the sub-dorsal marking (ovoid to saddle-shaped versus rounded in P. christyi), the waveshape of the EOD (with two main phases and a weak third phase in P. zakoni versus four phases in P. christyi) and presence / absence of Knollenorgan rosettes on the head (absent in P. zakoni versus present in P. christyi). Holotype (m) Paratypes (n = 10) Min – Max Mean Std – Dev Min – Max Median Meristic counts: Number of scale rows between the anterior base of 14 12 – 14 13 the anal fin and the lateral line (SDL) Number of teeth in the upper jaw (TUJ) 9 6 – 10 8 Number of teeth in the lower jaw (TL

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

distribution

Distribution (Fig. 1). Apparently endemic to the Congo basin. Abundant in Odzala. We collected P. zakoni n. sp. at several localities along the main channel of the Lékoli River at night. Elsewhere in the Congo basin, we have identified specimens of P. z a k o n i n. sp. from the Lower Congo (Pool Malebo) and from the Sangha River basin (unpublished observations). Electric organ discharge (Fig. 4 C). EOD waveforms produced by P. zakoni n. sp. are of relatively short duration among Petrocephalus (range = 0.164 – 0.281 msec), but they are, nevertheless, very similar in waveform to the EODs of several other Petrocephalus species. EOD sex differences are not apparent in the Odzala population. Statistics for waveform landmarks and other EOD measurements are provided by Lavoué et al. (2008). Electrocytes are assumed to be of type NPp based on characteristics of the EOD, although electrocyte anatomy has not yet been confirmed histologically.

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