Petrocephalus balayi Sauvage, 1883

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 : 519-523

Petrocephalus balayi Sauvage, 1883

( Figs 4B; 5B )

Mormyrus catostoma – Günther 1867: 116 (non Mormyrus catostoma Günther, 1866 ).

Petrocephalus balayi Sauvage, 1883: 159 .

Mormyrus ballayi – Sauvage 1884: 195.

Petrocephalus ballayi – Pellegrin 1908: 185. — Boulenger 1909: 52. — Gosse 1984: 108.

Mormyrus amblystoma Günther, 1896: 281 . — Boulenger 1909: 52.

TYPE MATERIAL. — Holotype of P. balayi : Gabon, Ogooué River , without more precision, Expedition Savorgnan de Brazza, Noël Ballay coll., ♀ 85.5 mm SL ( MNHN A 6297 ).

OTHER MATERIAL EXAMINED. — Gabon. Ogooué basin at Ngomo (Lower Ogooué), 00°49’S, 09°57’E (estimate), E. Haug coll., 1 specimen ( MNHN 1901- 505 ) ; 1 specimen ( MNHN 1906-159 ). — Coastal River Doumvou at Doumvou , 03°21’S, 10°44’E, 24.VII.2001, S. Lavoué and V. Mamonekene coll., 3 specimens ( MNHN 2002-260 ). — Basin of Rembo- Nkomi, River Moufoubou , 01°46’S, 10°08’E, 31.VII.2001, S. Lavoué and V. Mamonekene coll., 1 specimen ( MNHN 2002-261 ). — Coastal River Doumvou at Doumvou, 03°21’S, 10°44’E, 24.VII.2001, S. Lavoué and V. Mamonekene coll., 1 specimen (CU83327) .

DIAGNOSIS. — Petrocephalus balayi is distinguished from all other Petrocephalus species from Gabon by a combination of six characters: 10 to 12 scales between the anterior base of the anal fin and the lateral line; wide mouth in comparison with the other species in this area that possess a narrower mouth (width between 2.7 and 3.9 times in the head length [average 3.3]); very distinct sub-dorsal black spot on each side of the body; more than 27 small bicuspid teeth in only one series in the lower jaw; 20 to 22 branched rays in the dorsal fin and 26 to 27 in the anal fin.

DESCRIPTION

Counts and measurements are shown in the Table 2. Petrocephalus balayi is the largest species of this genus in Gabon (maximum size 126 mm SL). Body ovoid, longer than deep, and compressed. Height of body between 2.5 and 3.0 times in standard length, which gives this species a heavy aspect since the caudal peduncle is short. Head length is between 3.3 and 3.6 times in standard length. Head width between 1.6 and 2.2 times in head length. Snout short, wide and squareshaped. Mouth wide (ratio between head length and mouth width ranges from 2.7 to 3.9). Mouth sub-terminal, slightly ventral. Teeth small, bicuspid, with 28 to 38 in the lower jaw and 14 to 18 in the upper jaw. Eye relatively small. Eye diameter between 4.5 and 4.9 times in head length. Dorsal fin originates in the posterior half of the body (1.5 <SL/PDD <1.6). Pre-dorsal distance equal to, or slightly greater than pre-anal distance (1.0 <PDD/PAD <1.1). Scales cover the entire body, except for the head. Lateral line visible and complete, with 35 to 38 pored scales. Caudal peduncle relatively thick (CPL/CPD between 1.9 and 2.3), with 12 circumpeduncular scales. Skin on head thick, with numerous electroreceptors. Skin turns opaque with formalin fixation. Three rosettes of Knollenorgan electroreceptors present on head: the “Nakenrosette”, the “Kehlrosette” and the “Augenrosette”.

EOD CHARACTERISTICS

We recorded an EOD from just one female specimen ( Fig. 2B ). With a duration of 340 µs, it is shorter than those of either P. simus or P. microphthalmus , although the data are insufficient for statistical analysis ( Table 5). The third peak (P3) is only 4.5% of the peak-to-peak height for this specimen.

LIVE COLORATION

Body silver, slightly darker dorsally. The head is also slightly darker than the rest of the body. Iridescent reflections sometimes appear on the side depending on the orientation of light. Presence of a distinct sub-dorsal, black, round spot on each side of the body is characteristic for this species in Gabon. In addition, a black and ovoid mark is present at the base of the caudal peduncle. We did not observe any special coloration on the fins, which are translucent grey in color.

DISTRIBUTION ( Fig. 7 )

In Gabon, P. balayi occurs in the lower course of the Ogooué River and numerous associated lakes (Mbega pers. comm.), as well as in small coastal rivers south of the Ogooué to the border with Congo. Elsewhere, this species has been collected from the Congo basin ( David & Poll 1937; Poll 1939).

REMARKS

Lacking the holotype of Mormyrus amblystoma Günther, 1896 , we inspected the photograph provided by Harder (2000) and the drawing in the Catalogue of the Freshwater Fishes of Africa in the British Museum ( Boulenger 1909). Based on these and the original description ( Günther 1896), we agree with Boulenger’s (1898) synonymy with P. balayi . As in P. balayi , M. amblystoma has a sub-dorsal black spot, a wide mouth, a short snout and only 24 rays in the dorsal fin (including two or three unbranched rays). This combination of characters is diagnostic for P. balayi .

P. balayi is morphologically similar to P. sauvagii Boulenger, 1887 , which is known to occur in some coastal rivers of Cameroon, the lower course of the Niger basin and the central Congo basin. Both species live in sympatry in the Congo basin (pers. obs.). They can be easily distinguished one from the other by the number of the branched rays in the dorsal fin (26 to 28 for P. sauvagii vs 20 to 22 for P. balayi ) and in the anal fin (34 to 36 for P. sauvagii vs 26 to 27 for P. balayi ).

Petrocephalus microphthalmus Pellegrin, 1908 ( Figs 4C; 5C ; 6C )

Petrocephalus microphthalmus Pellegrin, 1908: 185 .

TYPE MATERIAL. — Holotype: Gabon, Ogooué basin at Ngomo (Lower Ogooué), 00°49’S, 09°57’E

A

B

C

D

(estimate), E. Haug coll., Ƌ 73.7 mm SL ( MNHN 1908-211).

OTHER MATERIAL EXAMINED. — Gabon. Ogooué basin at Ngomo (Lower Ogooué), 00°49’S, 09°57’E (estimate), E. Haug coll., 1 specimen ( MNHN 1906- 160 ) ; 1 specimen ( MNHN 1906-161 ). — Gabon, Ogooué basin from the tributary Ivindo at the confluence with the Nounah River , 01°11’N, 13°08’E, 11.VIII.1964, J. Géry coll., 7 specimens ( MNHN 1987-900 ). — Ogooué basin, tributary Ivindo at the rapids of Loa Loa, downstream of Makokou, 00°34N, 12°52’E, IX.1964, J. Géry coll., 1 specimen ( MNHN 1987-903 ). — Ogooué basin, tributary Ivindo at the rapids of Loa Loa, downstream of Makokou, 00°34N, 12°52’E, X.1964, J. Géry coll., 2 specimens ( MNHN 1987-904 ). — Ogooué basin, tributary Ivindo at the rapids of Loa Loa, downstream of Makokou, 00°34N, 12°52’E, 29.I.1998, C. D. Hopkins and S. Lavoué coll., 3 specimens ( MNHN 1998-722 ). — Gabon, Ogooué basin at Lambaréné, 00°42’S, 10°13’E, 20.X.1999, J. P. Friel, S. Lavoué and J. P. Sullivan coll., 3 specimens ( MNHN 2002-259 ). — Rembo- Nkomi basin, Moufoubou River at Moufoubou, 01°46’S, 10°08’E, VII.2001, S. Lavoué and V. Mamonekene coll., 1 specimen ( MNHN 2002-262 ). — Gabon, stream at Toucan downstream the bridge, 01°47’S, 09°53’E, 24.VII.2002, S. Lavoué and O. G. Pauwels coll., 6 specimens ( MNHN 2003-608 ). — Ogooué River at rocky point on Lambaréné Island facing Schweitzer Hospital, 00°42’S, 10°13’E, 20.IX.1999, J. P. Friel, S. Lavoué and J. P. Sullivan coll., 10 specimens ( MNHN 2003-700 ). — Ivindo River , mouth near Balé creek , 00°34’N, 12°52’E, 14.I.1998, C. D. Hopkins, S. Lavoué and J. P. Sullivan coll., 1 specimen (CU82207). — Ivindo River , boat landing, IRET Station , 00°34’N, 12°52’E, 15.I.1998, C. D. Hopkins, S. Lavoué and J. P. Sullivan coll., 1 specimen (CU82205). — Ogooué River , Okoloville , route from Franceville to Oroudja , 01°29’S, 13°31’E, 12.VIII.1999, M. E. Arnegard, C. D. Hopkins, J. P. Sullivan, A. Ngankale, M. Nganjobi and J. F. Liwouwou coll., 1 specimen (CU80491). — Ivindo River near Loa Loa , 00°34’N, 12°52’E, 19.I.1998, C. D. Hopkins, S. Lavoué, J. H. Mve Beh, M. J. Stiassny and E. Vreven coll., 1 specimen (CU82205). — Ogooué River , creek crossing road near Okoloville , 01°29’S, 13°31’E, 11.VIII.1999, M. E. Arnegard, C. D. Hopkins, J. P. Sullivan, A. Ngankale, M. Nganjobi and J. F. Liwouwou coll., 1 specimen (CU80479). — Ivindo River just below Loa-Loa rapids, 00°01’N, 12°49’E, 23.VIII.2001, C. D. Hopkins and M. E. Arnegard coll., 5 specimens (CU83104). — Ogooué River at rocky point on Lambaréné Island across from Hopital Schweitzer , 00°41’S, 010°13’E, 19.IX.1999, J. P. Friel, S. Lavoué and J. P. Sullivan coll., 15 specimens ( AMNH 233603 ). — Ivindo River just below Loa-Loa rapids, 00°31’N, 12°49’E, 23.VIII.2001, C. D. Hopkins and M. E. Arnegard coll., 11 specimens ( AMNH 233604 ). — Balé Creek under bridge, 00°31’N, 12°47’E, 16.I.1998, S. Lavoué and J. H. Mvé Beh coll., 1 specimen ( AMNH 233605 ) ; 1 specimen ( AMNH 233606 ) .

Congo. Ogooué basin from the Karagoua River, tributary of Ivindo, at Garabinzam, 01°38’N, 13°30’E, IX.1964, J. Géry coll., 1 specimen ( MNHN 1987- 902).

DIAGNOSIS. — Petrocephalus microphthalmus is distinguished from all other Petrocephalus species from Gabon by: few branched rays in the dorsal and anal fins (15 to 18 [average 16.5] and 23 to 27 [average 25.4], respectively); no more than 10 scales between the anterior base of the anal fin and the lateral line (range: 8- 10, average 9); a small eye (diameter between 4.1 and 4.8 times in head length [average 4.5]).

DESCRIPTION

Counts and measurements are summarized in Table 3. With a maximum standard length of 73.7 mm, P. microphthalmus is the smallest known species of Petrocephalus from Gabon. Body ovoid, longer than deep (SL/H between 2.7 and 3.2, average 3.0), and compressed. Snout short and rounded. Mouth narrow (3.5 <HL/ MW <4.9, average 4.2), situated just below the eye. Teeth small and bicuspid, with 10 in the upper jaw and 20 in the lower jaw. Dorsal fin occupies a posterior position on the body (1.5 <SL/PDD <1.7). Pre-dorsal distance equal to, or slightly greater than, pre-anal distance (1.0 <PDD/PAD <1.1). Scales cover the entire body, except for the head. Lateral line visible and complete, with 33 to 36 pored scales. Eight to 10 scales between the anterior base of the anal fin and the lateral line. Twelve scales around the caudal peduncle. Skin on head thick, with numerous electroreceptors. Skin turns opaque with formalin fixation. Knollenorgan electroreceptors appear as isolated receptor pores, but do not form “rosettes” in their typical positions on the head.

EOD CHARACTERISTICS

The EOD is 487 ± 142 µs in duration, with a peak FFT frequency at 4092 ± 942 Hz ( Fig. 2C ; Table 5). Peaks P1 and P2 are the same amplitude as in the other three species, but the third peak is reduced in amplitude (2.1% of peak-topeak height).

LIVE COLORATION

Body generally blue-grey, with the dorsum darker than the abdomen. The fish can appear metallic blue to violet depending on the angle of illumination. The color is especially intense on the operculum. Numerous chromatophores occur below the skin surface. Fins translucent except for the first dorsal fin rays, which are black.

DISTRIBUTION ( Fig. 7 )

In Gabon, this species is present throughout the Ogooué and Ntem basins, as well as in a small coastal river (Rembo Nkomi), which is situated just south of the mouth of the Ogooué and merges with the Ogooué in coastal lagoons. Elsewhere, Daget & Depierre (1980) identified some specimens from the Sanaga River ( Cameroon) as P. microphthalmus , but we were unable to examine them. Similarly, Poll (1967) identified some specimens from the Congo basin as P. microphtlamus , but these specimens were also not examined.

REMARKS

Bigorne & Paugy (1991) described P. microphthalmus as possessing a sub-dorsal black spot, but we did not observe this color pattern on any of the specimens we studied, including the holotype.

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. 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).

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.