Petrocephalus sauvagii ( Boulenger, 1887 )

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 : 29-32

Petrocephalus sauvagii ( Boulenger, 1887)

Mormyrus (Petrocephalus) sauvagii Boulenger (1887) : 149.

Mormyrus sauvagii Steindachner (1895) : 69.

Petrocephalus sauvagii Boulenger (1898) : 19 - Taverne (1972): 162 - Gosse (1984): 113. [Odzala field identification: Petrocephalus sp. 8, OTU 8]

Images. Fig. 10 A, photo of a live specimen from Odzala, Fig. 10 B, photo of a preserved specimen from Odzala and Fig. 14 , drawing of the holotype (BMNH 1887.1.13.3) from Boulenger (1909 –1916). Photo of the holotype in Harder (2000).

Type material. Holotype, BMNH 1887.1.13.3 "in the creeks of the Lower Congo and the tributary streams, without more precision, unknown coll."

Other specimens. We examined six specimens from Odzala and four additional specimens from the Lower Niger River (specimen list provided in the section "additional material examined").

Diagnosis. We prepared the following diagnosis using all the specimens of P. sauvagii that we examined, regardless their geographic origins. Petrocephalus sauvagii is distinguished from all other Petrocephalus species in Central Africa by the following combination of characteristics. Very wide mouth (HL/MW ≤ 3.7, range = 2.7–3.7) associated with a characteristic head shape when viewed from below. Twenty-four to 30 teeth in the upper jaw and 30–34 in the lower jaw. Anal fin with at least 32 branched rays (range = 32–38). Dorsal fin with at least 25 branched rays (range = 25–30). Mouth sub-terminal; ratio between the head length and the mouth position as large as 7.4 (range = 5.5–7.4). Pigmentation pattern with two melanin markings, sometimes of weak intensity or even scarcely visible: (1) an irregularly round black mark below the anterior base (first to fourth rays) of the dorsal fin; and (2) an ovoid blackish mark, often irregularly shaped, at the base of the caudal fin, extending onto the upper and lower fleshy lobes of the fin. EOD of normal polarity, with two main phases followed by a third, smaller phase.

Description. Table 8 provides morphometric ratios and meristic data for the holotype, six non-type specimens from Odzala and four non-type specimens from the Lower Niger River. However, the following description corresponds only to the six Odzala specimens we examined, except where separate reference is made to the holotype. Petrocephalus sauvagii is the largest Petrocephalus species occurring in the Odzala assemblage (maximum SL observed in Odzala = 189.0 mm, holotype = 146.7 mm). Body ovoid, longer than high (2.7 ≤ SL/H ≤ 3.4, average = 3.0, holotype = 2.9) and laterally compressed. Head length between 3.5 and 3.7 times in standard length (average = 3.6, holotype = 3.7). Eye small (4.1 ≤ HL/ED ≤ 4.5, average = 4.3, holotype = 4.6). Snout very short (6.3 ≤ HL/SNL ≤ 9.9, average = 8.0, holotype = 6.7) and round. Mouth distinctively large (3.1 ≤ HL/MW ≤ 3.7, average = 3.3, holotype = 3.1), sub-terminal (5.5 ≤ HL/MP ≤ 7.4, average = 6.6, holotype = 4.9), opening just under the anterior half of the eye. Dentition consisting of many small bicuspid teeth, 24–30 (median = 26, holotype = 26) in a single row in the upper jaw, 30–34 (median = 32, holotype = 30) in a single row in the lower jaw. Dorsal and anal fins originate in the posterior half of the body (1.5 ≤ SL/PDD ≤ 1.6 and 1.5 ≤ SL/PAD ≤ 1.7). Pre-dorsal distance equal to, or slightly greater than, preanal distance (1.0 ≤ PDD/PAD ≤ 1.1). Anal fin with 33–38 branched rays (median = 35, holotype = 34).

Dorsal fin with 26–30 branched rays (median = 28, holotype = 27). Scales cover the body, except for the head. Lateral line visible and complete with 38–41 (median = 39, holotype = 36) pored scales along its length. Twelve to 16 scales (median 14, holotype = 14) between the anterior base of the anal fin and the lateral line. Caudal peduncle relatively thin (2.3 ≤ CPL/CPD ≤ 3.1, average = 2.6, holotype = 2.7). Twelve scales around the caudal peduncle. Skin on head thick, becoming opaque with formalin fixation, with Knollenorgan electroreceptors organized into three relatively small rosettes.

Holotype Specimens Specimens from

(m) from Odzala Lower Niger

(n=6) (n=4)

Min–Max Mean Std–Dev Min–Max Mean Std–Dev Live coloration ( Fig. 10 A). Body uniformly white-silver with metallic iridescence. Two characteristic melanin markings are present, sometimes with very weak intensity in large individuals: (1) an irregular round mark below the anterior base (first to fourth rays) of the dorsal fin; (2) an ovoid blackish mark, often irregular in shape, centered at the base of the caudal fin and extending onto the upper and lower fleshy lobes of this fin. The fins themselves (caudal fins and others) are translucent.

Distribution ( Fig. 1 ). Petrocephalus sauvagii is the only species of Petrocephalus known to occur in both the Congo and Niger basins. There is no record of this species occurring in the Lower Guinea province. The holotype was collected from " the creeks of the Lower Congo and the tributary streams " without more precision being given on the exact locality ( Boulenger, 1887). In Odzala, we collected P. sauvagii at several localities along the main course of the Lékoli River and, exclusively at night, in some small tributary creeks flowing through savannah.

Electric organ discharge ( Fig. 10 C). EOD recordings are only available for three individuals. Thus, generalizations about the EOD features of this species must be made with caution. EOD waveforms of all three individuals are of somewhat short duration for the genus (range = 0.232 – 0.273 msec), but they are, nevertheless, very similar to EODs of several other Petrocephalus species. Statistics for waveform landmarks and other EOD measurements for P. sauvagii are provided by Lavoué et al. (2008), who demonstrated histologically that the electrocytes of this species are type NPp.

Remarks. We noticed some morphological differences between allopatric specimens of P. sauvagii from the Niger and Congo basins. Specimens from the Niger basin possess fewer anal fin rays (32–33 versus 33– 38), a longer snout (HL/SNL = 5.5–6.8 versus 6.3–9.9) and a greater interorbital width (HL/IOW = 2.6–2.7 versus 3.5–4.2) than Odzala specimens.

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 10. Petrocephalus sauvagii 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 waveforms. One EOD was arbitrarily selected from each recorded individual and superimposed with the other recordings (N = number of 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 8. Principal morphometric ratios and meristic counts for the holotype (BMNH 1887.1.13.3), six specimens from Odzala (CU 87864, CU 89082, CU 92387) and four specimens from Lower Niger (MNHN 1990 - 942) of Petrocephalus sauvagii (Abbreviations: m = male; Std – Dev = standard deviation; Min – Max = minimum – maximum).

Standard length (mm)	146.7	109.2–189.0 156.2 33.3	118.7–127.7	122.0 3.9
Head length (mm)	50.3	31.1–51.6 43.6 8.6	31.2–32.9	32.0 0.8
Ratio of standard length (SL):
SL/body height (H)	2.9	2.7–3.4 3.0 0.3	2.5–2.7	2.6 0.1
SL/head length (HL)	3.7	3.5–3.7 3.6 0.1	3.8–3.9	3.8 0.0
SL/pre-dorsal distance (PDD)	1.6	1.5–1.6 1.6 0.1	1.6–1.6	1.6 0.0
SL/pre-anal distance (PAD)	1.6	1.5–1.7 1.6 0.1	1.6–1.7	1.6 0.0
SL/dorsal fin length (DFL)	4.5	4.2–4.7 4.5 0.2	4.1–4.5	4.3 0.2
SL/anal fin length (AFL)	3.6	3.1–3.4 3.3 0.1	3.2–3.3	3.2 0.1
SL/caudal peduncle length (CPL)	6.3	6.1–7.7 7.0 0.8	6.0–6.2	6.1 0.1
SL/mouth width (MW)	11.4	11.2–12.9 11.9 0.6	10.2–12.4	11.7 1.0
Ratio of head length (HL):
HL/snout length (SNL)	6.7	6.3–9.9 8.0 1.5	5.5–6.8	5.9 0.6
HL/mouth width (MW)	3.1	3.1–3.7 3.3 0.2	2.7–3.2	3.1 0.2
HL/eye diameter (ED)	4.6	4.1–4.5 4.3 0.1	4.0–4.2	4.1 0.1
HL/interorbital width (IOW)	3.5	3.5–4.2 3.8 0.3	2.6–2.7	2.7 0.1
HL/head width (HW)	2.1	1.8–2.4 2.1 0.3	1.7–1.9	1.8 0.1
HL/mouth position (MP)	4.9	5.5–7.4 6.6 0.9	4.4–5.4	5.0 0.4
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD)	2.7	2.3–3.1 2.6 0.4	2.6–2.8	2.7 0.1