Petrocephalus Marcusen, 1854

Lavoué, Sébastien, Hopkins, Carl D. & Toham, André Kamdem, 2004, The Petrocephalus (Pisces, Osteoglossomorpha, Mormyridae) of Gabon, Central Africa, with the description of a new species, Zoosystema 26 (3), pp. 511-535 : 514-518

Genus Petrocephalus Marcusen, 1854

Petrocephalus simus Sauvage, 1879 ( Figs 4A; 5A ; 6A )

Petrocephalus simus Sauvage, 1879: 100 .

Mormyrus simus – Sauvage 1880: 51. — Günther 1896: 292.

TYPE MATERIAL. — Syntypes: Gabon, Ogooué River at the type locality Doumé (near the modern city of Lastoursville, Gabon, 00°51’S, 12°56’E [estimate]), Expedition Savorgnan de Brazza, Alfred Marche coll., 2 ♀♀ 91.2 and 93.1 mm SL ( MNHN A 0892).

OTHER MATERIAL EXAMINED. — Gabon. Ogooué basin, tributary Ivindo at the confluence with the Nounah River, 01°11’N, 13°08’E, 26.I.1998, C. D. Hopkins, S. Lavoué and J. P. Sullivan coll., 13 specimens ( MNHN 1998-0717). — Ogooué basin, tributary Ivindo at the confluence with the Nounah River, 01°11’N, 13°08’E, XI.1964, J. Géry coll., 22 specimens ( MNHN 1987-905). — Ogooué basin, tributary Ivindo at the rapids of Loa Loa, downstream of Makokou, 00°34’N, 12°52’E, 11.XI.1964, J. Géry coll., 10 specimens ( MNHN 1987-906). — Ogooué basin, tributary Ivindo at the rapids of Loa Loa, downstream of Makokou, 00°34’N, 12°52’E, XI.1964, J. Géry coll., 2 specimens ( MNHN 1987- 907). — Ogooué basin at Lambaréné, 00°42’S, 10°13’E, IX.1999, J. P. Friel, S. Lavoué and J. P. Sullivan coll., 2 specimens ( MNHN 2002- 253). — Ogooué basin at Cap Lopez, 00°40’S, 08°50’E (estimate), 1885, Bois Guillaume coll., 1 specimen ( MNHN 1885-411). — Nyanga basin, Moukalaba River nearby the ferry at Mougambou, 02°47’S, 10°43’E, 2. VII.2001, S. Lavoué and V. Mamonekene coll., 7 specimens ( MNHN 2002- 254). — Basin of Rembo-Nkomi, Moufoubou River at Moufoubou, 01°46’S, 10°08’E, VII.2001, S. Lavoué and V. Mamonekene coll., 7 specimens ( MNHN 2002-255). — Ogooué basin at Lambaréné, 00°42’S, 10°13’E, IX.1999, J. P. Friel, S. Lavoué and J. P. Sullivan coll., 4 specimens ( MNHN 2002- 256). — Ogooué basin, River Onoy, 01°50’S, 11°15’E, 18. VII.2001, S. Lavoué and V. Mamonekene coll., 1 specimen ( MNHN 2002-257). — Ogooué River at the National Park of La Lopé, 00°06’S, 11°35’E, 20. VIII.2001, M. E. Arnegard, C. D. Hopkins, S. Lavoué and T. Uschold coll., 18 specimens ( MNHN 2002-258). — Mbari River, stream at Toucan downstream the bridge, 01°47’S, 09°53’E, 24. VII.2002, S. Lavoué and O. G. Pauwels coll., 1 specimen ( MNHN 2003-607). — Beneath Ogooué River bridge West of Franceville, 01°38’S, 13°31’E, 11. VII.1999, M. E. Arnegard, J. P. Sullivan and A. Lehman coll., 1 specimen ( AMNH 233593). — Louétsi River couple 100 m downstream of Bongolo Bridge, 02°14’S, 11°27’E, 21. VII.1999, J. P. Sullivan and J. Beck coll., 1 specimen (CU80322). — Ntem River near auberge d’Ayengbe, 02°13’N, 11°44’E, 7.IX.1999, J. P. Friel, S. Lavoué and J. P. Sullivan coll., 1 specimen (CU80924). — Ogooué basin, tributary Ivindo at the confluence with the Nounah River, 01°11’N, 13°08’E, 27.I.1998, C. D. Hopkins, S. Lavoué and J. P. Sullivan coll., 4 specimens (CU). — Beneath Ogooué River bridge West of Franceville, 01°38’S, 13°31’E, 7. VIII.1999, M. E. Arnegard, J. P. Sullivan and A. Lehman coll., 1 specimen (CU80539). — Ntem River, “Deghe” creek near auberge d’Ayengbe, 02°13’N, 11°44’E, 3.IX.1999, J. P. Friel, S. Lavoué and J. P. Sullivan coll., 1 specimen (CU80699). — Ogooué River, upstream point of Lambaréné Island, 00°42’S, 10°13’E, 11. VII.1999, M. E. Arnegard and J. P. Sullivan coll., 4 specimens (CU80242). — Ogooué River, north part of Lambaréné Island in rocks, 00°42’S, 10°13’E, 17. VII.1999, M. E. Arnegard, P. Guinsoumbi and J. P. Sullivan coll., 2 specimens (CU80254). — Ntem River just in front of auberge d’Ayengbe, 02°17’N, 11°33’E, 4.IX.1999, J. P. Friel, S. Lavoué and J. P. Sullivan coll., 4 specimens ( AMNH 233595). — Ogooué River at rocky point on Lambaréné Island across from Hôpital Schweitzer, 00°41’S, 10°13’E, 19.IX.1999, J. P. Friel, S. Lavoué and J. P. Sullivan coll., 2 specimens ( AMNH 233596). — Louetsi River at Bongolo dam below bridge, 02°14’S, 11°27’E, 14.IX.1998, J. P. Sullivan and J. Beck coll., 1 specimen ( AMNH 233599).

Cameroon. Ntem basin, without more precision, 1906, A. Cottes coll., 4 specimens ( MNHN 1907- 153). — Ntem basin, River Mboua which is a tributary of Kom at Ekowong, 02°31’N, 12°11’E, 21.IV.1995, A. Kamdem Toham coll., 8 specimens ( MRAC 93-108-P-37-48). — Ntem basin, near the south part of Ma’an, 02°19’N, 10°38’E, 9.XII.1994, A. Kamdem Toham coll., 2 specimens ( MRAC 95- 030-P-299-300).

DIAGNOSIS. — Petrocephalus simus is distinguished from all other Petrocephalus species from Gabon by a combination of five characters: a minimum of 19 branched rays on the dorsal fin, very rarely 18 (range: 18-27; median: 22); a minimum of 11 scales, rarely 10 (range: 10-16; median: 12.4), between the anterior base of the anal fin and the lateral line; a subterminal mouth in which the ratio between the head length and the mouth position is between 3.8 and 6.3 (average of 4.7); a moderately wide mouth (width between 4.1 and 6.1 times in the head length, average of 5.0); and absence of a black spot near the base of the dorsal fin on either side of the body.

DESCRIPTION

Counts and measurements are shown in Table 1. Petrocephalus simus is a medium sized species (maximum SL observed: 105.7 mm). Body ovoid, longer than high (2.6 <SL/H <3.4) and compressed. Head length between 3.4 and 4.3 times in standard length. Snout short and round. Mouth relatively narrow (4.1 <HL/ MW <6.1), sub-terminal, just under the anterior half of the eye. Teeth small and bicuspid, 8 to 14 in a single row in the upper jaw, 16 to 22 in the lower jaw. Dorsal fin originates in the posterior half of the body (1.5 <SL/PDD <1.8). Pre-dorsal distance equal to, or slightly greater than, the preanal distance (1.0 <PDD/PAD <1.1). Scales cover the body, except for the head. Lateral line visible and complete with 36 to 44 pored scales along its length. Caudal peduncle relatively thin (2.0 < CPL / CPD <3.7, average 2.8), although specimens from the Nyanga River basin have thicker caudal peduncles (2.2 < CPL / CPD <2.5, average 2.37). Twelve scales around the caudal peduncle. Skin on head thick, with numerous electroreceptors. Skin turns opaque with formalin fixation. Three rosettes of Knollenorgan electroreceptors are present on the head: the “Nakenrosette” behind the eye and dorsal to the opercular flap, the “Kehlrosette” anterior to the pectoral fin, and the “Augenrosette” anterior and slightly dorsal to the eye (see Harder 2000).

EOD CHARACTERISTICS

EODs from this species are illustrated in Figures 1 and 2A . The electric discharge waveform begins

D Petrocephalus sullivani n. sp. P1 0

-20 dB -40

-60 P2 100 10,000 0.1 ms Frequency in Hz

Lavoué S. et al.

with a head-positive phase (P1) of approximately 26% of peak-to-peak height, followed by a larger, head-negative phase (P2) with an amplitude of 74% of peak-to-peak height, followed by a third phase (P3) with an amplitude of 5.1%. The overall duration of the pulse is 436 ± 142 µs. The FFT of the EOD peaks at 4995 Hz ( Table 5).

LIVE COLORATION

Body silver, slightly darker dorsally including the head. Sub-dorsal round black spot never present on the side, as some authors have mentioned previously. Fins translucent, except for the first rays of the dorsal fin, which appear black. Moreover, the first external rays of the caudal fin are pigmented black, in a crescent shape centred on the base of the caudal fin.

DISTRIBUTION ( Fig. 7 )

In Gabon, P. simus has a widespread distribution. This species occurs in the entire Ogooué River basin, as well as the basins of the Ntem, the Rembo Nkomi and the Nyanga in the southern part of Gabon. Outside Gabon, P. simus was until recently considered to have a widespread distribution, stretching out to almost all hydrographical basins of West Africa and Central Africa (including the Congo basin), from Liberia to Angola. It has been commonly recorded outside Gabon ( Pellegrin 1936; Poll 1939, 1967; Daget 1954, 1962; Matthes 1964), but see Discussion.

REMARKS

Populations of P. simus from the Ivindo and Ntem systems are morphologically closer to each other than are populations from other parts of Gabon. In particular, individuals from Ntem and Ivindo populations possess fewer branched dorsal rays (18 to 23 [average 21.34] vs 21 to 27 [average 23] for remaining populations, largely from the Ogooué) and anal rays (25 to 28 [average 27] vs 27 to 31 [average 28]), and they have fewer scales between the anterior extremity of the anal fin and the lateral line (10 to 13 [average 11] vs 12 to 16 [average 14]).

Figures

FIG. 5. — Drawing of specimens of Petrocephalus; A, P. simus Sauvage, 1879 (syntype, MNHN A 0892) (from Boulenger 1909-1916); B, P. balayi Sauvage, 1883 (holotype of Mormyrus amblystoma Günther, 1896, BMNH 1896.5.5) (from Boulenger 1909-1916); C, non type specimen of P. microphthalmus Pellegrin, 1908 from Angola (from Poll 1967); D, P. sullivani n. sp. (holotype, MNHN 2003-619, 93.1 mm SL). Scale bars: 1 cm.

FIG. 6. — Photos of live specimens of Petrocephalus; A, P. simus Sauvage, 1879 (from the Ivindo River, near Loa Loa, CU75445, 56 mm SL); B, P. sullivani n. sp. (from the Ogooué River, near La Lopé, CU83120, 109 mm SL); C, P. microphthalmus Pellegrin, 1908 (Ogooué River, near Franceville, CU80479, 64 mm SL). Photographs by Carl D. Hopkins.

FIG. 1. — Electric organ discharge (EOD) waveform of Petrocephalus simus Sauvage, 1879 with landmarks indicated by symbols. Head positive is upward in this and all other EOD plots. Open circles mark the start and end of the waveform, defined as the first and last points that deviate from the baseline by at least 1.5% of the peak-to-peak height. P1, P2, and P3 mark three peaks in the waveform. Zero-crossings, indicated by open squares, are used to delimit the beginning and end of phase P2. The sampling rate in this example was 250 kHz.

FIG. 2. — Representative electric organ discharge (EOD) waveforms (left) and power spectra of EODs (right) superimposed for 31 individuals representing four species of Petrocephalus from Gabon. Individual field numbers are listed to the left. All EOD recordings are made with head-positivity upward. EODs have been normalized to the same peak-to-peak height and centered around the midpoint between peaks P1 and P2.

FIG. 7. — Geographical distribution in Gabon of Petrocephalus simus Sauvage, 1879 (●), P. balayi Sauvage, 1883 (■), P. microphthalmus Pellegrin, 1908 (◆) and P. sullivani n. sp. (O).