Mormyrus cyaneus Roberts and Stewart, 1976
Species overview
Medium-sized fish, body elongate, head longer than body depth, snout funnel-shaped, blunt, slightly bent down, mouth terminal. No conspicuous cutaneous sensory organs below the eye. Light blue, uniform or darker blue on head and back, countershaded.
Size observed: 260 mm SL.
M. cyaneus(measurements)
Taxonomic description
-Body rather elongate, laterally compressed, cross section oblong-oval, body depth 20-23 % SL, greatest depth at origin of dorsal fin.
-Head length 25-28 % SL; head depth 16-18 % SL, 79-87 % body depth.
-Outline of back (dorsal fin inclusive) convex, upper profile of head between opercular cleft and eye stronger convex, upper profile of snout slightly concave or convex, underside of head concave, outline of belly slightly convex up to caudal fin, no step at base of anal fin.
-Snout more or less bluntly funnel-shaped, slightly compressed and bent down, 40-44 % head length, 80-98 % postorbital length.
-Mouth small, 10-14 % head length, terminal, edge of mouth far away from anterior nostril, edge of upper jaw on a level with lower edge of opercular cleft.
-Chin with moderate submental swelling, lower jaw as thick as or slightly thicker than upper part of snout.
-Teeth: neither shape nor number indicated in description.
-Nostrils separate, more or less oval, depending on size of the specimen, anterior or posterior nostril on a level with lower rim of eye; their axis cutting axis of head at an angle of about 30°.
-Eye in an oval orbit, its diameter 12-15 % head length, 25-29 % postorbital length. No conspicuous cutaneous sensory organs below the eye.
-Opercular cleft curved, 30-40 % head length, 45-59 % head depth.
-Dorsal fin 51-59 fin-rays, base of D 45-51 % SL, anal fin rays no indicated in description, base of A 18-20 % SL, not forming a step between outlines of belly and caudal peduncle; origin of D far before origin of A, slightly before pelvic fin, end of D far behind end A; predorsal length 37-40 % SL, preanal length 53-59 % SL.
-Pectoral fin rounded, originating at lower end of opercular cleft, ending well before base of pelvic fin. V is slightly closer to A than to P.
-Caudal fin obtusely pointed, rather large, the scaled lobes obtusely pointed, covering 3/4 of the entire fin. Number of scales in lateral line and round caudal peduncle not indicated.
-Caudal peduncle 11-13 % SL, its depth 4-5 % SL 33-43 % its length.
-Coloration »Uniformly light blue or uniformly blue on the body with head dark blue or blackish blue, no iridescence« countershaded.
Type locality
»Zaïre River mainstream near Inga hydroelectric dam (5° 31.5 ‘ S 13° 57.5 ‘ E)«, Rapids of Congo river, Central Zaïre district, Democratic Republic of Congo.
Distribution
Type locality.