Petrocephalus similis Lavoué 2011

Adapted from Lavoué, 2011:

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, holo- type = 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).

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.

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.

119 mm SL maximum observed size.

Adapted from Lavoué, 2011:

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/silver-white 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. simus by its mouth opening under the posterior half of the eye (vs. the anterior half of the eye in P. simus); its relatively deep caudal peduncle (CPL/CPD = 2.2–2.6, mean = 2.4; holotype = 2.3 vs. 2.8 in P. simus) 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. simus). Petrocephalus similis can be further distinguished from P. sullivani, 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 andPetrocephalus 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 boveiValenciennes in Cuvier & Valenciennes 1847, by its fewer branched rays in the dorsal and anal fins and its larger maximum standard length (Bigorne & Paugy 1991).