Petrocephalus frieli, Lavoué, 2012

Lavoué, Sébastien, 2012, Petrocephalus Marcusen, 1854 (Osteoglossomorpha: Mormyridae) of the Bangweulu-Mweru ecoregion (Luapula River system, Congo basin), with the description of a new species, Journal of Natural History (J. Nat. Hist.) 46 (35 - 36), pp. 2159-2178 : 2170-2173

Petrocephalus frieli sp. nov.

( Figure 3A, B )

Type specimens

Holotype. CU 96866; Zambia (Northern province on label), Congo basin, Luapula River, Samfa Rapids at pontoon on Chambeshi River , Chambeshi River , (10.85 ◦ S, 31.17 ◦ E) (station JPF 05-047); coll. Bills, Chilala and Friel, 11 October 2005 (sexually mature male, 90.7 mm SL).

Paratypes (10). Zambia, Congo basin: CU 91152; same locality, date and collectors as the holotype (five specimens including one sexually mature male, 47.1–87.8 mm SL) (CU DNA tissue 363). CU 91140; Luapula River , Central Luapula River at Luapula River Bridge (12.11 ◦ S, 29.85 ◦ E) (station JPF 05-006); coll. Bills, Chilala and Friel, 22 September 2005 (one sex undetermined specimen, 60.0 mm SL) (CU DNA tissue: 41). CU 91144; Luapula River , Lake Bangweulu shoreline at rocky point near Samfya Ferry dock (11.35 ◦ S, 29.56 ◦ E) (station JPF 05-014A); coll. Bills, Chilala and Friel, 24 September 2005 (three sex undetermined specimens, 52.9–66.7 mm SL). CU 91146; Luapula River, Lake Bangweulu shoreline at rocky point near Samfya Zambian Fisheries Offices (11.37 ◦ S, 29.65 ◦ E) (station JPF 05-015); coll. Bills, Chilala and Friel, 25 September 2005 (one sex undetermined specimen, 57.2 mm SL) .

Diagnosis

Petrocephalus frieli sp. nov. is distinguished from all other Petrocephalus spp. of Central Africa (i.e. Lower Guinea and Congo provinces) by the following combination of characteristics: body coloration brownish without an intense subdorsal pigmentation mark; 21 to 24 branched rays in the dorsal fin (mean = 23) and 28–30 branched rays in the anal fin (mean = 29); more than 13 scale rows between the anterior base of the anal fin and the lateral line; three distinct electroreceptive rosettes on the head.

Description

Morphometric ratios and meristic data for the holotype and paratypes are presented in Table 2. Maximum SL observed = 90.7 mm (holotype). Body ovoid longer than high (mean SL/H = 2.9) and laterally compressed. Head length 3.6 times (mean) in standard length. Snout short (mean HL/ SNL = 6.0) and round. Mouth small (mean HL/ MW = 4.2), sub-terminal, opening under the posterior half of the eye. Teeth small and bicuspid, a median of 11 teeth in a single row in the upper jaw, a median of 20 teeth in a single row in the lower jaw. Dorsal and anal fins originate in the posterior half of the body (mean SL/ PDD = 1.6 and mean SL/ PAD = 1.7). Predorsal distance slightly greater than the pre-anal distance (1.0 ≤ PDD/PAD ≤ 1.1). Median dorsal fin branched rays of 23. Median anal fin branched rays of 29. Scales cover the body, except for the head. Lateral line visible and complete, with a median of 38 pored scales along its length. Twelve scales around the caudal peduncle. Median of 16 scales between the anterior base of the anal fin and the lateral line. Caudal peduncle thin (mean CPL / CPD = 2.7). Skin on head thick, turning opaque with formalin fixation. Knollenorgans visible, clustered into the three distinct rosettes of Harder (1968) .

Petrocephalus frieli sp. nov. can be distinguished from the otherwise similar P. squalostoma , occurring in sympatry in the Lake Bangweulu region, by its number of branched rays in the dorsal fin (median = 23, range 21–24 versus median = 20, range 15–22 in P. squalostoma ) – this results in a longer dorsal fin in P. frieli sp. nov. ( Figure 3B, C ) – and its deeper body (mean SL/H = 3.3, range 3.0–3.6 versus mean = 2.9, range 2.7–3.2 in P. squalostoma ). Petrocephalus frieli sp. nov. differs from P. c. haullevillii , P. c. congicus , P. mbossou , P. microphthalmus , P. schoutedeni , P. valentini and P. zakoni by the presence of three very distinct Knollenorgan-type clusters in the head. Petrocephalus frieli sp. nov. also differs from P. grandoculis and P. sauvagii by the lower number of branched rays in the dorsal fin (median = 25, range 24–26 in P. grandoculis and median = 28, range 26–30 in P. sauvagii ) and anal fin (median = 31, range 30–32 in P. grandoculis and median = 35, range 33–38 in P. sauvagii ). Petrocephalus frieli sp. nov. can be further distinguished from P. simus by its mouth opening under the posterior half of the eye (versus the anterior half of the eye in P. simus ) and its relatively larger mouth (HL/MW = 4.2, range 3.7–4.9 versus 5.3, range 4.4–7.3 in P. simus ). Finally, P. frieli sp. nov. can be further distinguished from P. c. catostoma by the number of scales around the caudal peduncle (12 versus 15/ 16 in P. c. catostoma ) ( Kramer and van der Bank 2000).

Live coloration

Body background colour silver-white with metallic reflection on the flanks, darker on the snout, forehead and along the dorsal edge until the caudal peduncle ( Figure 3B ). Presence of a very faded subdorsal spot below the anterior part of the dorsal fin only on the specimens from Lake Bangweulu. Not observed in the other specimens. Scattered melanophores over the body, denser and larger on the head. All fins whitish, translucent, with melanophores marking the lepidotrichia.

Petrocephalus frieli sp. nov. differs from P. balayi , P. binotatus , P. christyi , P. mbossou , P. odzalaensis , P. pulsivertens and P. zakoni by the absence of any distinct black marking, including the absence of a distinct subdorsal spot.

Distribution

Petrocephalus frieli sp. nov. is restricted to the southern part of the Bangweulu-Mweru ecoregion, from the Chambeshi River to Lake Bangweulu and the upper Luapula River, downstream to Lake Bangweulu ( Figure 1 ).

Electric organ discharge

Unknown. Electrocyte anatomy not examined.

Remarks

The specimens of P. frieli sp. nov. from Lake Bangweulu differ from the riverine specimens from the Chambeshi River and the upper Luapula River in having a pale melanin pattern, with an attenuated subdorsal roundish mark, the first dorsal fin rays and the base of the pectoral fin blackish, a croissant-shaped mark centred at the base of the caudal fin, and the eyes circled with denser melanophores. They are otherwise indistinguishable; therefore I interpret this geographical difference in the marking pattern as of intra-specific level.

Etymology

Dedicated to Dr John P. Friel, curator at the Cornell University Museum of Vertebrates (CUMV), in recognition of his contribution to African ichthyology and for his care of the large collection of African electric fish deposited at CUMV. In addition, John P. Friel is one of the collectors of this new species.

Figures

Figure 1. Map of Africa (top right) showing the location of the Congo basin. The first inset at centre details the topography of the Congo River and its main tributaries and rapids/falls sections. The second inset (bottom left) provides a detailed map of the Bangweulu-Mweru ecoregion (comprising the Luapula River basin), located in the southeastern-most part of the Congo River basin. The filled circle indicates the type locality of the new species Petrocephalus frieli sp. nov.; open circles indicate additional localities. The filled triangle indicates the type locality of Petrocephalus squalostoma; open circles indicate additional localities. Filled diamond marks the estimated location of the first specimen identified as Petrocephalus simus by Boulenger (1920) (identification uncertain, see text for details).

Figure 3. Photographs of Petrocephalus frieli sp. nov. and Petrocephalus squalostoma from the Bangweulu-Mweru ecoregion, Luapula River system, Congo basin. (A) Preserved holotype of P. frieli sp. nov. (CU 96866, scale bar 1.0 cm) (photograph by John P. Sullivan, CUMV). (B) Live specimen of P. frieli sp. nov. of about 8.0 cm [estimated] standard length (photograph by Roger Bills, SAIAB). (C) Live specimen of P. squalostoma of about 8.0 cm [estimated] standard length (photograph by Roger Bills, SAIAB).