Gnathonemus petersii (Günther, 1862)
Species overview
Medium sized fish, body moderately deep, head sharp-snouted, bases of unpaired fins of nearly equal length, margins concave; snout funnel shaped, mouth terminal, barbel long and thick. Size observed: 350 mm SL.
G. petersii(measurements)
Taxonomic description
-Body moderately deep, laterally compressed, 22-29 % SL, greatest depth between pelvic and anal fin; head length 24-28 % SL, head depth 17-22 % SL, 68-79 % body depth.
-Outlines of back and belly slightly convex, upper profile of head concave, underside of head convex, curving into base of barbel.
-Snout obtusely pointed, 30-39 % head length, 56-77 % postorbital length.
-Mouth terminal, small, edge of mouth far away from anterior nostril, upper jaw on a level with upper edge base of pectoral fin.
-Chin with long and thick cylindrical barbel, directed forward in life.
-Teeth notched, 3-5/ 5-6.
-Nostrils separate, anterior above, posterior below centre of eye, anterior circular, posterior oval, 25-30 % snout length away from eye; axis of nostrils cutting axis of head at an angle of about 45° .
-Eye 12-17 % head length, 19-33 % postorbital length.
-Opercular cleft 29-41 % head length, 38-49 % head depth, curved.
-Dorsal 25-31 fin-rays, its base 18-23 % SL, anal 32-36 rays, its base 22-29 % SL, D originating behind origin of A, ending before end of A; margin of both D and A concave. Predorsal length 61-67 % SL, preanal length 55-61 % SL.
-Pectoral fin obtusely pointed, originating close to lower half of opercular cleft, extending beyond middle of pelvic fin, which is closer to P than to A..
-Caudal fin pointed, both scaled lobes and blades. 57-70 scales in lateral line. 8 (10) scales round caudal peduncle.
-Caudal peduncle 11-20 % SL, its depth 5-6 % SL, 28-43 % its length.
-Coloration, black, in life with yellow shine, two white bars between of D and A, anterior rays of these fins black, next ones more and more fading.
-Caudal fin with dark outer rays, inner rays yellowish or colourless.
(Mr. E. Schraml saw and photographed an albino Gnathonemus petersii 5 at a pet fish dealer. Considering that albinism is nothing really astounding among fishes, a Japanese dealer paid an exorbitant prize of 8000 DM for this animal).
Type locality
G. petersii: »Old Calabar (West-Africa)« (04° 57 ‘ N °08 19’ E).
G. brevicaudatus: »Riv. Gribingui, Congo français, Shari basin (00° 26 ‘ N 12° 48 ‘ E).
Distribution
West african rivers from lower Niger to Zaïre basins, Gribingui (Shari or Chari basin, 12° 58 ‘ N 14° 31 ‘ E), l’ Ogun (07° 0 ‘ N 03° 40 ‘ E) Bassin de la Cross (5° 40 ‘ N 08° 10 ‘ E).
Electric organ discharges
G. petersii(elec. organ)
G. petersii(EOD)