Petrocephalus similis, Lavoué, Sébastien, 2011

Lavoué, Sébastien, 2011, A new species of Petrocephalus Marcusen 1854 (Osteoglossomorpha: Mormyridae) from the Sanaga River basin, Cameroon, Zootaxa 2934, pp. 20-28 : 23-25

Petrocephalus similis n. sp.

( Fig. 2 , Table 1)

Holotype. CU 95318 (107.9 mm SL male), Cameroon, Adamaoua Province, Sanaga River basin, Djerem River near Mbakaou Village, (6.21° N, 12.75° E), D.T. Reid, July 2006.

Paratypes. CU 93218, 4 spec. (108.9 mm SL sex undetermined, 104.9 mm SL sex undetermined, 101.3 mm SL male, 103.8 mm SL male), same collection data as holotype. — CU 93219, 3 spec. (104.6 mm SL male, 91.8 mm SL male, 97.9 mm SL male), same collection data as holotype. — CU 93221, 4 spec. (118.5 mm SL male, 106.1 mm SL male, 106.1 mm SL sex undetermined, 106.2 mm SL male), same collection data as holotype. — MNHN 1978-0720, 1 spec. (110.4 mm SL sex undetermined). Cameroon, Adamaoua Province, Sanaga River basin, Djerem River, just downstream of Lake Tibati (=Mbakaou Reservoir), ~ 6.3° N, 12.8° E, D. Depierre.

Diagnosis. Petrocephalus similis is distinguished from all other Petrocephalus species of Central Africa (i.e., Lower Guinea and Congo provinces) by the following combination of characteristics: body coloration gold/silverwhite without melanin mark; 22–24 branched rays in the dorsal fin and 28 or 29 branched rays in the anal fin. Petrocephalus similis can be further distinguished from P. s i m u s by its mouth opening under the posterior half of the eye (vs. the anterior half of the eye in P. s i m u s); its relatively deep caudal peduncle (CPL/CPD = 2.2–2.6, mean = 2.4; holotype = 2.3 vs. 2.8 in P. s i m u s) and its greater number of scale rows between the anterior base of the anal fin and the lateral line (16 or 17 versus 12 in P. s i m u s). Petrocephalus similis can be further distinguished from P. s u l - livani, by its proportionally larger mouth (HL/mouth width = 3.9–4.5, mean = 4.2, holotype = 4.4 vs. 4.8 in P. sullivani , wider head (HL/head width = 1.6–1.9, mean = 1.8, holotype = 1.7 vs. 2.0 in P. sullivani ), and its shorter caudal peduncle (SL/CPL = 6.3–7.5, mean = 6.8, holotype = 7.1 vs. 6.3 in P. sullivani ).

From the six Nilo-Sudanian species occurring in the Niger and Chad basins bordering the upper Sanaga, P. similis is easily distinguished from Petrocephalus pallidomaculatus Bigorne & Paugy in Lévêque et al. 1990, Petrocephalus soudanensis Bigorne & Paugy in Lévêque et al. 1990 and Petrocephalus ansorgii Boulenger 1903 by its complete absence of large melanin sub-dorsal spot, from Petrocephalus bane ( Lacepède 1803) and Petrocephalus sauvagii ( Boulenger 1887) , by its smaller mouth and fewer branched rays in the dorsal and anal fins, and from Petrocephalus bovei Valenciennes in Cuvier & Valenciennes 1847, by its fewer branched rays in the dorsal and anal fins and its larger maximum standard length ( Bigorne & Paugy 1991).

Description. Morphometric ratios and meristic data for the holotype and paratypes are presented in Table 1. Petrocephalus similis is a relatively large sized species within the genus (maximum observed SL = 118.6 mm; holotype = 107.9 mm). Body ovoid, 2.9–3.3 times longer than high (paratype average = 3.0, holotype = 2.9) and laterally compressed. Head length 3.8–4.2 times in SL (paratype average = 4.0, holotype = 3.9). Snout short (4.3 ≤ HL/SNL ≤ 5.8, paratype average = 5.0, holotype = 5.3) and round. Mouth small (3.9 ≤ HL/MW ≤ 4.5, paratype average = 4.2, holotype = 4.4), sub-terminal, opening under the posterior half of the eye. Teeth small and bicuspid, 8–11 in a single row in the upper jaw (paratype median = 10, holotype = 9), 19–23 in a single row in the lower jaw (paratype median = 21, holotype = 21). Dorsal and anal fins originate in the posterior half of the body (1.5 ≤ SL/ PDD ≤ 1.6 and 1.6 ≤ SL/PAD ≤ 1.7, respectively). Pre-dorsal distance slightly greater than the pre-anal distance (1.0 ≤ PDD/PAD ≤ 1.1). Dorsal fin with 22–24 branched rays (paratype median = 23, holotype = 24). Anal fin with 28 or 29 branched rays (paratype median = 29, holotype = 29). Scales cover the body, except for the head. Lateral line visible and complete with 36–40 (paratype median = 39, holotype = 38) pored scales along its length. Twelve scales around the caudal peduncle. Fifteen to 17 scales (paratype average = 16, holotype = 17) between the anterior base of the anal fin and the lateral line. Caudal peduncle thin (2.2 ≤ CPL/CPD ≤ 2.6, paratype average = 2.4, holotype = 2.3). Twelve scales around the caudal peduncle. Skin on head thick, turning opaque with formalin fixation. Knollenorgans visible, clustered into the three distinct rosettes of Harder (1968).

Live coloration ( Fig. 2 A). Body background color gold/silver-white with metallic reflection on the head, darker dorsally from the midline. No large melanin spot or mark on side below dorsal fin and at the base of the pectoral fins and the caudal fin. All fins whitish-yellowish, mostly translucent.

Holotype Paratypes (n=12)

Range Mean Std. Dev. Standard length (mm) 107.9 91.8–118.6 105.1 6.6 Head length (mm) 37.7 29.6–39.8 35.1 2.6

Ratio of standard length (SL):

SL/body height (H) 2.9 2.9–3.3 3.0 0.1 SL/head length (HL) 3.9 3.8–4.2 4.0 0.1 SL/pre-dorsal distance (PDD) 1.6 1.5–1.6 1.6 0.0 SL/pre-anal distance (PAD) 1.7 1.6–1.7 1.7 0.0 SL/dorsal-fin length (DFL) 4.3 4.3–4.6 4.4 0.1 SL/anal-fin length (AFL) 3.3 3.3–3.7 3.4 0.1 SL/caudal peduncle length (CPL) 7.1 6.3–7.5 6.8 0.4 SL/mouth width (MW) 17.4 15.4–17.7 16.5 0.8

Ratio of head length (HL):

HL/snout length (SNL) 5.3 4.3–5.8 5.0 0.4 HL/mouth width (MW) 4.4 3.9–4.5 4.2 0.2 HL/eye diameter (ED) 3.6 3.5–3.8 3.7 0.1 HL/interorbital width (IOW) 2.8 2.4–3.1 2.8 0.2 HL/head width (HW) 1.7 1.6–1.9 1.8 0.1 HL/mouth position (MP) 3.6 2.9–3.6 3.1 0.2

Ratio of caudal peduncle length (CPL):

CPL/caudal peduncle depth (CPD) 2.3 2.2–2.6 2.4 0.1

Range Median

Meristic counts:

Scale rows between the anterior base of the anal fin 17 15–17 16 and the lateral line (SDL)

Number of upper jaw teeth (TUJ) 9 8–11 10 Number of lower jaw teeth (TLJ) 21 19–23 21

Distribution ( Fig. 1 ). Endemic to the upper Sanaga basin. Petrocephalus similis is known from two adjacent localities along the course of the Djerem River (upper Sanaga basin), slightly downstream of the Mbakaou (Tibati) Reservoir.

Electric organ discharge. Unknown. Electrocyte anatomy not studied; all Petrocephalus species examined to date have electric organ of type "NPp" (i.e., the electrocytes have non-penetrating cellular stalks arising from their posterior face ( Bass 1986; Lavoué et al. 2010; Sullivan et al. 2000)).

Remarks. Based on identity of museum records from the Sanaga River basin, P. s im il is has probably been confused several times with P. s i m u s, due to the conspicuous absence of a large melanin spot on the side beneath the dorsal fin, the overall similarity of the body, with few distinctive characteristics. Petrocephalus simus is endemic to the lower part of the Lower Guinea province; its occurrence is restricted to the following rivers (from north to south): Ntem, Woleu, Ogooué, Nyanga and Kouilou-Niari (Hopkins et al. 2007).

Etymology. The specific epithet " similis " is given in reference to the resemblance between this new species and P. sullivani .

Figures

FIGURE 1. Map of the hydrographic system of Cameroon (top-left inset showing the location of Cameroon in Africa). The Sanaga River basin is highlighted with deep grey lines. The boundaries among the faunal regions are indicated with black dashed lines. The filled black circle indicates the type locality of Petrocephalus similis n. sp. and the open circle indicates the second known locality.

FIGURE 2. Petrocephalus similis n. sp. from Djerem River near the village of Mbakaou, Adamoua province, Cameroon. A. Photograph of a live specimen ~ 100 mm SL showing coloration in life (CU 93219), photo by Duncan T Reid. B. Photograph of the preserved holotype (CU 95318, scale bar = 1.0 cm), photo by John P. Sullivan. C. Photograph of a preserved paratype (MNHN 1978 - 0720), photo by Claude Ferrara.