Petrocephalus ballayi Sauvage, 1883
Species overview
Smaller fish, body rather short and deep, head long, slightly longer than deep, snout very short, shorter than diameter of eye, slightly protruding mouth, Three aggregations of cutaneous sensory organs on the head, »rosettes«, present. Base of dorsal fin steeply falling, base of anal fin steeply rising to caudal peduncle. Silvery with dark back, countershaded, a black spot at base of caudal, another below origin of dorsal fin.
Size observed: 157 mm SL.
P. ballayi(measurements)
Taxonomic description
-Body moderately short, strongly laterally compressed, body depth 32-38 % SL, greatest depth above origin of anal fin.
-Head length 28-33 % SL; head depth 23-30 % SL, 68-83 % body depth.
-Outline of back slightly convex, upper profile and underside of head convex, outline of belly slightly convex.
-Snout strongly rounded, protruding mouth, very short, 13-18 % head length, 21-31 % postorbital length.
-Mouth moderately inferior, 19-35 % head length, its edge below centre of eye, upper jaw on a level with upper edge base of pectoral fin.
-Chin inconspicuous.
-Teeth notched, 20-24/30-36.
-Nostrils closely together, upright-oval, distance between nostrils about half their distance from eye; axis parallel axis of head.
-Eye big, its diameter 16-29 % head length, 87-167 % snout length, 22-52 % postorbital length. Three aggregations of cutaneous sensory organs, electrorecpetors of the type tuberous organs, on the head, »rosettes« present: above the eye and above and below the opercular cleft.
-Opercular cleft strongly curved, 32-56 % head length, 32-58 % head depth.
-Dorsal fin 21-25 fin-rays, base of D 19-24 % SL, anal fin 28-30 rays, base of A 24-28 % SL, origin of D more or less opposite origin of A, end of D before end of A; predorsal length 59-65 % SL, preanal length 57-62 % SL.
-Pectoral fin pointed, extending to 3/4 the length of pelvic fin. V is closer to P than to A.
-Caudal fin pointed, scaled at the base. 35-37 scales in lateral line; (10-)12 round caudal peduncle.
-Caudal peduncle 15-20 % SL, its depth 6-8 % SL, 32-45 % its length.
-Coloration »Brown above, silvery below [countershaded]; a black spot on the root of the caudal, and another below origin of dorsal«.
Type locality
P. ballayi: »Riv. Ogôué (Congo français)« Gabon; M. amblystoma: »Talagouga, Ogowe« Gabon.
Distribution
Congo basin (Central basin) and Ogowe River, Gabon.