Gnathonemus histrio Fowler, 1936
Species overview
Medium sized fish, moderately deep, body oblong, head sharp-snouted, snout obtusely pointed, mouth terminal with thick, long barbel. Blackish brown with lighter belly, dark bar bordered white between unpaired fins. Size observed: 158 mm SL, 180 mm TL.
G. histrio(measurements)
Taxonomic description
-Body laterally compressed, oblong ovoid, moderately deep, body depth 28-31 % SL, greatest depth between pelvic and anal fin.
-Outlines of back and belly slightly convex, upper profile and underside of head convex.
-Head length 26-28 % SL, head depth 20-23 % SL, about 3/4 body depth.
-Snout obtusely pointed, straight, length 30-33 % head length, bluntly conical with terminal mouth.
-Mouth small, width about 4 % head length, edge of mouth far away from anterior nostril, upper jaw on midline of head.
-Chin forming a thick, long barbel, half as long as head, directed forward-downward in life.
-Teeth notched, 2-5/3-5.
-Nostrils separate, anterior circular, level with upper rim of eye and above posterior which is oval and level with centre of eye. Distance posterior nostril - eye about 2/3 eye diameter, distance anterior nostril front equal distance between nostrils; axis of nostrils cuts axis of head at an angle of about 45°.
-Eye small, 11-14 % head length.
-Opercular cleft curved, 34-38 % head length, about 45 % head depth.
-Dorsal fin 24 rays, base of D 20-21 % SL, anal 31 rays, base of A 26-27 % SL. D originating behind origin of A, ending before end of A.
-Outlines of D and A convex. Predorsal length 67-70 % SL, preanal length 60-63 % SL.
-Pectoral fin obtusely pointed, originating close to middle of opercular cleft, extending to middle of pelvic fin which is closer to P than to A.
-Caudal fin with obtusely pointed scaled and membranous lobes. 47-49 scales in lateral line, 8 round caudal peduncle.
-Caudal peduncle 14-16 % SL, its depth 6-7 % SL, 44-48 % its length.
-Coloration, blackish brown, belly little lighter, a crescent shaped dark band between anterior rays of D and A, bordered white, fins blackish. According to Fowler (l. c.): »Light brown to pale or whitish generally, contrasted with darker. On head many minute, close-set dark dots, darker behind eye and below and before pectoral, also entire medial side of trunk «
Type locality
G. histrio: Fort Sibut, Ubangi Shari (00° 30 ‘ S 17°42 ‘E).
G. barbatus : »Caluango, riv. Camalao, affl. riv. Luange« (08° 21 ‘ S 19° 40 ‘E) Angola, Congo basin.
Distribution
Congo basin and Angola.