Hyperopisus bebe (Lacepède, 1803)
Species overview
Large fish, body elongate, moderately deep, head about as long deep, snout short, mouth terminal, dorsal fin very short, anal fin more than four times as long as dorsal fin.
Size observed: 510 mm SL.
H. bebe(measurements)
Taxonomic description
-Body elongate, laterally compressed, moderately deep, body depth 19-25 % SL, greatest depth between pelvic and anal fin, belly keeled.
-Head about as long as deep, head length 18-23% SL, head depth 13-18 % SL, 75-78 % body depth.
-Outline of back slightly curved, outline of belly stronger curved; front profile moderately curved, gular profile slightly convex; Snout not protruding mouth, directed strictly forward, snout 21-27 % head length, 34-40 % postorbital length.
-Mouth small, terminal, upper jaw on a level with lower margin of eye, edge of mouth below anterior nostril.
-Chin with slight submental swelling.
-Teeth in jaws small, notched, 3-5/ 5-6; on parasphenoid and tongue a pavement of large sphaeroid teeth.
-Nostrils separate, circular, nearer front than eye, lower nostril on a level with centre of eye, anterior above it, the axis arranged at an angle of about 60° to axis of head.
-Eye small, 8-12 % head length, 13-20 % postorbital length.
-Opercular cleft S-shaped, 31-41 % head length, 44-60 % head depth.
-Dorsal fin, 12-16 fin-rays, base of D very short, 6-9 % SL, steeply inclined to caudal peduncle; anal fin 52-71 rays, base very long, 35-41 % SL. Origin of D far behind that of A, end of D clearly before end of A; predorsal length 72-78 % SL, preanal length 45-54 % SL.
-Pectoral fin pointed, extending to base or to middle of pelvic fin. V is clearly nearer P than A.
-Caudal fin obtusely pointed, scaled lobe covers 4/5 of C. 93-120 scales in lateral line; 16-20 (22) round caudal peduncle.
-Caudal peduncle 28-63 % its depth.
-Coloration Silvery with much darker back, olive, brown or yellowish, speckled with black dots in adults, belly greyish, throat greyish or whitish, fins mottled grey.
Type locality
Hyperopisus bebe bebe: »Lieu dit Bébé« Egypt, to day: Bilbays, Nile delta, (30° 25 ‘ N 31° 34 ‘ E)
Hyperopisus dorsalis: »Nil (Egypte)«,
Hyperopisus bebe occidentalis: »West Africa« Niger,
Hyperopisus bebe charienis: »Chad«.
Hyperopisus tenuicauda: »Riv. Chari, à Fort-Archambault (Congo français)0«,
Distribution
»Nile basin (up to Albert and Murchison Niles)« »Senegal, Niger, Volta and Gambia rivers, Lake Chad, Riv. Ouémé (Dahomey)«, »Lago Margherita«, to day: Lake Abaya, Ethiopia.
Electric organ discharges
Biphasic, head positive, +/- with small. low negative precursor and positve overshoot at the end, about 1.5 msec.
Remark
Of Hyperopisus bebe two subspecies and several synonyms have been described. A re-examination of the various type specimens and non-types has shown a wide overlap in both meristics and proportions. This means that the differences in the presumed subspecies most probably are due to local conditions. The species occurs in rivers as well as in lakes in the Sahelo-Soudanian region from Guinea in the west to south Ethiopia in the east. This wide range of distribution also means great differences in ecological conditions. (See also Bigorne, 1990.)