Petrocephalus grandoculis Boulenger, 1920

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 : 35-38

Petrocephalus grandoculis Boulenger, 1920

Petrocephalus grandoculis Boulenger (1920) : 10.

[Odzala field identification: Petrocephalus sp. 10, OTU 10]

Images. Fig. 12 A, photo of a live specimen from Odzala, Fig.12 B, photo of a preserved specimen from Odzala and Fig. 14 , drawing of one syntype from Boulenger (1920), p. 10. Photo of two syntypes in Harder (2000).

Type material. Syntypes, BMNH 1919.9.10.16–17 [examined] and MRAC 7158, 7167 [not examined]. Leopoldville (Kinshasa), Zaire ( Democratic Republic of the Congo)[estimated 4.25 ° S, 15.33 ° E].

Other specimens. We also examined two specimens from Odzala National Park (specimen list provided in the section “additional material examined”).

Diagnosis. The following diagnosis is based on all examined specimens of P. grandoculis , regardless their geographic origins. Petrocephalus grandoculis is distinguished from all other Petrocephalus species in Central Africa by the following combination of characteristics. Very small mouth (5.2 ≤ HL/MW ≤ 6.1). Eight to 11 teeth in the lower jaw. Upper jaw with 18–22 teeth. Eye large (2.8 ≤ HL/ED ≤ 3.2). Snout short (6.5 ≤ HL/SNL ≤ 10.7). Dorsal fin with 24–26 branched rays. Anal fin with 30–33 branched rays. Pigmentation pattern consists of two melanin markings (black patches): (1) a distinct, although generally weak, round black mark on each side of the body below the anterior base of the dorsal fin (first to fifth rays); and (2) a crescentlike mark at the base of the caudal fin on each side, not extending onto the rayed portions of the upper and lower caudal fin lobes. EOD of normal polarity.

Min–Max Min–Max

Meristic counts:

Number of scale rows between the anterior base of 15– 15 13–15 11 the anal fin and the lateral line (SDL)

Number of teeth in the upper jaw (TUJ) 10–11 8–8 12 Number of teeth in the lower jaw (TLJ) 19–20 18–22 14 Description. Table 10 provides morphometric ratios and meristic data for the two Kinshasa syntypes and, separately, for the two non-type specimens from Odzala National Park. The following description applies to the two Odzala specimens, with separate reference to the two syntypes. Petrocephalus grandoculis is a medium-sized species within the genus Petrocephalus (maximum SL observed = 97.8 mm). Body ovoid, longer than high (2.5 ≤ SL/H ≤ 2.7, syntypes = 3.0–3.1) and laterally compressed. Head length 3.8–4.2 times in standard length (syntypes = 3.9–4.1). Eye quite large (2.8 ≤ HL/ED ≤ 3.1, syntypes = 3.1–3.2). Snout short (6.5 ≤ HL/SNL ≤ 10.7, syntypes = 6.5–6.7) and round. Mouth very small (5.2 ≤ HL/MW ≤ 5.9, syntypes = 5.7–6.1), sub-terminal, opening under the anterior half of the eye. Teeth small and bicuspid, only eight (syntypes = 10 or 11) in a single row in the upper jaw, 18–22 (syntypes = 19 or 20) in a single row in the lower jaw. Dorsal and anal fins originate in the posterior half of the body [SL/PDD = 1.6 and SL/PAD = 1.7 (syntypes = 1.7–1.8), respectively]. Pre-dorsal distance slightly greater than pre-anal distance (1.0 ≤ PDD/ PAD ≤ 1.1). Dorsal fin with 25–26 branched rays (syntypes = 24–26). Anal fin with 32 or 33 branched rays (syntypes = 30 or 31). Scales cover the body, except for the head. Lateral line visible and complete with 37–39 (syntypes = 38) pored scales along its length. Caudal peduncle relatively thin (2.2 ≤ CPL/CPD ≤ 3.0, syntypes = 3.0). Twelve scales around the caudal peduncle. Skin on head thick, becoming opaque with formalin fixation. The numerous Knollenorgan electroreceptors on the head are clearly organized into two visible rosettes (Augenrosette and Nackenrosette). In our examination of specimens, we were uncertain about the definitive presence of the third rosette, the Kehlrosette, as this structure did not appear to us to be as distinct as it is in other species (e.g., P. binotatus ). However, more definitive recent analysis using toluidine blue staining of the skin now suggests that the Kehlrosette is present, but smaller and harder to discern than in other Petrocephalus (M. Hollmann and B. A. Carlson, unpub. obs.).

Live coloration ( Fig. 12 A). Body mostly white-silver. Dorsum slightly darker than the rest of the body. Pigmentation pattern consists of two melanin markings: (1) a distinct, but weak, round black mark below the anterior base of the dorsal fin (first to fifth rays); and (2) a crescent-shaped mark at the base of the caudal fin, which does not extend onto the rayed portions of the upper and lower caudal fin lobes. No black mark is present at the base of pectoral fins. The fins themselves are translucent.

Distribution ( Fig. 1 ). Endemic to the Congo basin. The type locality is situated on the Lower Congo River at Kinshasa. In Odzala, we collected only two specimens of P. grandoculis from the main channel of the Lékoli River.

Electric organ discharge ( Fig. 12 C). EODs have only been recorded from one individual of P. grandoculis , which was collected in Odzala National Park. The EOD duration for this individual (0.380 msec, based on 1.5% deviations from baseline) and the general appearance of the waveform are typical for Petrocephalus . Statistics for waveform landmarks and other EOD measurements are provided by Lavoué et al. (2008). Electrocyte anatomy is unknown, although it is expected to be type "NPp" as deduced from the EOD waveform.

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 12. Petrocephalus grandoculis of the Lékoli River system of Odzala National Park, Republic of the Congo. A. Photograph of a live specimen (no scale). B. Photograph of a preserved specimen (scale bar = 1.0 cm). C. EOD waveform. One EOD was arbitrarily selected from the only individual of this species recorded in Odzala, an obvious male. The EOD is shown here head-positive up (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 10. Principal morphometric ratios and meristic counts for the two syntypes (BMNH 1919.9.10.16 - 17) and two specimens from Odzala (CU 88119, CU 92385) of Petrocephalus grandoculis Boulenger, 1920 and the holotype (CU 92389) of Petrocephalus mbossou n. sp., (Abbreviations: o = sex category " other " [i. e., not an obvious mature male, but rather a female or immature male]; Min – Max = minimum – maximum).

	P. grandoculis Syntypes (n=2)	P. grandoculis Odzala specimens (n=2)	P. mbossou n. sp. Holotype (o)
	Min–Max	Min–Max
Standard length (mm)	74.0–76.0	88.0–97.8	127.1
Head length (mm)	18.4–19.0	23.0–23.5	36.9
Ratio of standard length (SL):
SL/body height (H)	3.0–3.1	2.5–2.7	3.0
SL/head length (HL)	3.9–4.1	3.8–4.2	3.4
SL/pre-dorsal distance (PDD)	1.6–1.6	1.6–1.6	1.7
SL/pre-anal distance (PAD)	1.7–1.8	1.7–1.7	1.6
SL/dorsal fin length (DFL)	4.2–4.6	4.0–4.1	4.4
SL/anal fin length (AFL)	3.3–3.3	3.1–3.3	4.3
SL/caudal peduncle length (CPL)	5.8–6.1	5.3–6.7	5.2
SL/mouth width (MW)	23.6–23.6	21.7–22.4	16.2
Ratio of head length (HL):
HL/snout length (SNL)	6.5–6.7	6.5–10.7	5.4
HL/mouth width (MW)	5.7–6.1	5.2–5.9	4.7
HL/eye diameter (ED)	3.1–3.2	2.8–3.1	3.7
HL/interorbital width (IOW)	3.4–3.7	3.2–3.8	4.3
HL/head width (HW)	2.1–2.2	1.8–1.9	2.2
HL/mouth position (MP)	3.7–4.0	4.5–5.0	2.8
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD)	3.0–3.0	2.2–3.0	2.9