Petrocephalus binotatus Pellegrin, 1924

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 : 6-9

Petrocephalus binotatus Pellegrin, 1924

Petrocephalus binotatus Pellegrin (1924) : 1.

[Odzala field identification: Petrocephalus sp. 1, OTU 1]

Images. Fig. 3 A, photo of a live specimen from Odzala, Fig. 3 B, photo of a preserved specimen from Odzala and Fig. 14 , drawing of the holotype (MRAC 15191) from Pellegrin (1928), p. 12. Photo of the holotype in Harder (2000).

Type material. Holotype, MRAC 15191 [examined], sex undet., 83.2 mm SL. Democratic Republic of the Congo, Congo River at Ikengo [estimated geographic coordinates: 0.13° S, 18.13° E], H. Schouteden coll.

Other specimens. We have examined 35 additional specimens from Odzala National Park (see "additional material examined").

Diagnosis. The following diagnosis is based on all examined specimens of P. binotatus , regardless their geographic origins. Petrocephalus binotatus is distinguished from all other Petrocephalus species from Lower Guinea and Congo provinces by the following combination of characteristics. Dorsal fin shorter than the anal fin (1.5 ≤ AFL/DFL, range = 1.5–1.7). Dorsal fin with at least 20 branched rays (range = 20–24). Anal fin with at least 30 branched rays (range = 30–33). Sixteen teeth or fewer (range = 8–16) in the upper jaw, 24 teeth or fewer (range = 19–24) in the lower jaw. Eye relatively large (HL/ED ≤ 4.0, range = 3.5–4.0). Mouth sub-terminal; ratio of head length to mouth position (HL/MP) between 3.9 and 6.1. Unique pigmentation pattern with the presence of three well defined black patches: (1) a distinct (although sometimes covering only few scales), more or less round/oval, black mark situated slightly anterior to the dorsal fin on each side of the body; (2) a black mark at the base of each pectoral fin; (3) an ovoid black mark centered at the base of the caudal fin that does not extend onto the upper and lower fleshy lobes of this fin. EOD of normal polarity (i.e., first major phase head-positive).

Description. This description corresponds to the Odzala material (e.g., ranges, averages, medians), except where explicit reference is made to the holotype (from Ikengo). Morphometric ratios and meristic data for non-type specimens from Odzala and the holotype are presented in Table 1 . Petrocephalus binotatus , described by Pellegrin (1924), is a small sized species within the genus Petrocephalus (maximum SL observed in Odzala = 88.4 mm, holotype = 83.2 mm). Body ovoid, longer than high (2.3 ≤ SL/H ≤ 2.8, average = 2.5, holotype = 2.4) and laterally compressed. Head length of Odzala specimens between 3.7 and 4.0 times in standard length (average = 3.9, holotype = 3.6). Snout short (6.8 ≤ HL/SNL ≤ 8.3, average = 7.8, holotype = 5.5) and round. Eye large (3.5 ≤ HL/ED ≤ 4.0, average = 3.6, holotype = 3.6). Mouth small (4.4 ≤ HL/MW ≤ 5.2, average = 4.7, holotype = 3.2), sub-terminal, opening under the anterior half of the eye. Teeth small and bicuspid, 8 to 16 (median = 10) in a single row in the upper jaw, 19 to 24 (median = 21) in the lower jaw. Dorsal and anal fins originate in the posterior half of the body (1.5 ≤ SL/PDD ≤ 1.6) and (1.6 ≤ SL/PAD ≤ 1.7), respectively. Pre-dorsal distance slightly greater than the pre-anal distance (1.0 <PDD/PAD ≤ 1.1). Dorsal fin with 20–22 branched rays (median = 21, holotype = 24). Anal fin with 30–33 branched rays (median = 32, holotype = 33). Scales cover the body, except for the head. Lateral line visible and complete with 37 or 38 pored scales along its length. Eleven to 13 scales (median = 12), between the anterior base of the anal fin and the lateral line. Caudal peduncle thin (1.8 ≤ CPL/CPD ≤ 2.2, average = 2.0, holotype = 2.3). Twelve scales around the caudal peduncle. Skin on head thick, becoming opaque with formalin fixation. Three distinct rosettes of Knollenorgans are present on the head (Augenrosette, Nackenrosette and Kehlrosette).

Min–Max Median

Meristic counts:

Number of scale rows between the anterior base of the anal 11 11–13 12 fin and the lateral line (SDL)

Number of teeth in the upper jaw (TUJ) 8–16 10 Number of teeth in the lower jaw (TLJ) 19–24 21 Live coloration ( Fig. 3 A). Body uniformly white-silver, with the presence of three characteristic melanin marks on each side of the body: (1) a distinct, approximately round/oval black mark situated slightly anterior to the dorsal fin, sometimes covering only a few scales; (2) a black spot at the base of the pectoral fin; (3) an ovoid black mark centered at the base of the caudal fin that does not extend onto the upper and lower parts of the caudal fin. Fins translucent.

Distribution ( Fig. 1 ). Apparently endemic to the Congo River basin. Holotype from the locality Ikengo on the Congo River just below Mbandaka. One of the most abundant Petrocephalus species in Odzala. We collected P. binotatus at several localities along the main channel of the Lékoli River. At the time of our collections, however, this species appeared to be absent from small tributary creeks flowing through the forest or savannah.

Petrocephalus binotatus was absent in two recent collections from the Lower Congo River made in the vicinities of the Pool Malebo (one collection by M. Stiassny and B. Schelly in 2002, housed in the American Museum of Natural History; the other by P. Feulner and F. Kirschbaum in 2006, housed in the Leibniz Institute of Freshwater Ecology and Inland Fisheries, Berlin; pers. obs. of material contained in these collections).

Electric organ discharge ( Fig. 3 C). Petrocephalus binotatus males and females produce EODs with overall waveforms that are typical for the genus, being similar to EODs produced by many other congeners. However, this is one of the few Petrocephalus species (e.g., the only Petrocephalus species in Odzala National Park) for which possible EOD sex differences have been detected thus far in field recordings. As with other Petrocephalus species exhibiting possible sex differences, magnitudes of the differences between males and females are small. In Odzala, for example, mean EOD duration (± std. dev.) is 0.330 ± 0.074 msec in obvious adult males and 0.270 ± 0.033 msec in other adult and sub-adult individuals, based on 1.5% voltage deviations from baseline relative to peak-peak amplitude. Statistics for waveform landmarks and other EOD measurements are provided by Lavoué et al. (2008) for specimens recorded in Odzala National Park. No EOD recordings are available for the holotype or other specimens collected near the type locality (Ikengo, Congo River, Fig. 1 ). Electrocytes are assumed to be of type NPp based on characteristics of the EOD, although electrocyte anatomy has not yet been confirmed histologically.

Remarks. Specimens of P. binotatus from Odzala resemble the holotype described from the main channel of the Congo River (locality Ikengo, Fig. 1 ) ( Pellegrin, 1924). However, they also exhibit several differences, mainly in head morphology. The holotype has a larger mouth (HL/MW = 3.2 versus ≥ 4.4 in Odzala specimens), a longer snout (HL/SNL = 5.5 versus ≥ 6.8 in Odzala specimens) and a larger interorbital width (HL/IOW = 2.3 versus ≥ 2.6 in Odzala specimens). Additional comparative material from the type locality and other localities in the Congo basin are necessary to determine the taxonomic implications of these differences.

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 3. Petrocephalus binotatus of the Lékoli River system of Odzala National Park, Republic of the Congo. A. Photograph of a live specimen (no scale: the photo has been maximally enlarged to better illustrate details of body shape, melanin patterning, etc.). B. Photograph of a preserved specimen (scale bar = 1.0 cm). C. EOD waveforms displayed separately for obvious males and other individuals (see text). One EOD was arbitrarily selected from each recorded individual and superimposed with the other recordings (N = number of individuals, given separately for obvious males and all other individuals). All EODs are scaled to the same peak-to-peak voltage, and they are plotted (head-positive up) on the same time scale as overlays centered on the largest positive peak of each waveform (scale bar = 0.2 msec).

FIGURE 14. Historical illustrations of Petrocephalus species described from Congo or Lower Guinea that occur in Odzala. The drawings were reproduced from the following sources: Petrocephalus binotatus from Pellegrin (1928); Petrocephalus balayi from Boulenger (1909 – 1916); Petrocephalus microphthalmus from Poll (1967); Petrocephalus christyi from Boulenger (1920); Petrocephalus sauvagii from Boulenger (1909 – 1916); and Petrocephalus grandoculis from Boulenger (1920).

Tables

TABLE 1. Principal morphometric ratios and meristic counts for the holotype (MRAC 15191) and seven specimens from Odzala (CU 88063, CU 88079, CU 88076, CU 88074, CU 87838, CU 88041, CU 88091) of Petrocephalus binotatus (Abbreviations: m = male; Std – Dev = standard deviation; Min – Max = minimum – maximum).

	Holotype (m)	Specimens from Odzala (n=7)
		Min–Max Mean Std–Dev
Standard length (mm)	83.2	65.0–88.4 76.0 8.1
Head length (mm)	23.1	17.3–21.9 19.6 1.6
Ratio of standard length (SL):
SL/body height (H)	2.4	2.3–2.8 2.5 0.2
SL/head length (HL)	3.6	3.7–4.0 3.9 0.1
SL/pre-dorsal distance (PDD)	1.6	1.5–1.6 1.6 0.0
SL/pre-anal distance (PAD)	1.7	1.6–1.7 1.7 0.0
SL/dorsal fin length (DFL)	4.5	4.2–4.9 4.7 0.3
SL/anal fin length (AFL)	2.8	2.8–3.3 3.0 0.2
SL/caudal peduncle length (CPL)	7.0	6.5–7.6 7.1 0.4
SL/mouth width (MW)	11.6	17.3–18.2 20.3 1.0
Ratio of head length (HL):
HL/snout length (SNL)	5.5	6.8–8.3 7.8 0.5
HL/mouth width (MW)	3.2	4.4–5.2 4.7 0.3
HL/eye diameter (ED)	3.6	3.5–4.0 3.6 0.2
HL/interorbital width (IOW)	2.3	2.6–3.0 2.8 0.2
HL/head width (HW)	1.9	1.8–1.9 1.8 0.0
HL/mouth position (MP)	3.9	4.4–6.1 5.1 0.6
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD)	2.3	1.8–2.2 2.0 0.2