Papyrocranus afer (Günther, 1868)
Species overview
Body shape typically for a knife fish, but with rather straight back. Pelvic fins absent. Of the cranial dermal bones only the preopercle is serrated. The most striking internal character is the extension of diverticula of the swimbladder into the cranial bones. There is considerable geographical variation in coloration. Hardly to be separated from the other species of the genus.
Size observed: up to 80 cm.
Taxonomic description
-Body strongly laterally compressed, greatest depth between origins of pectoral and anal fins.
-Head longer and not as wide as compared to the other species of the genus, P. congoensis; its upper profile straight to slightly concave, its underside slightly convex.
-Outline of back sligthly convex or straight, no hump; outline of body along base of anal fin convex.
-Mouth terminal, its edge slightly behind posterior rim of eye.
-Opercular cleft long, curved. Origin of pectoral fin slightly above level of edge of mouth, length of pectoral extends to origin of anal fin. Pelvic fins absent.
-Dorsal fin with short base present.
-Anal fin long, 121-141 fin-rays, merging in the caudal fin, 12-14 fin-rays, but there may be a slight inflection between the two parts of the fin blades. 77-85 vertebrae.
-Coloration, there "are at least four distinct geographical colour variaties. In Ghana, Sierra Leone, most of Liberia and at least part of Guinea (Corubal and Kolenté) it usually has moderately numerous pale spots (mainly on lower half of the body) on a dark background on body and anal fin. Specimens from the Cavally basin (Liberia, Côte d'Ivoire) are very striking with numerous and relatively large pale spots (white or yellow in life ?) covering entrire body and anal fin.
Most specimens from Cross River basin (Cameroun), on the other hand, have no spots and are uniformly dark or even black. Finally, specimens from the Upper Niger basin (Bamako, and Diafarabé) and some coastal rivers basins in Guinée (Haute Gambié, Casamance, Kogon) tend to have scattered small round dark spots on body and pale spots or dark and pale marbling on anal fin." (Roberts, 1992: 377.
Type locality
>Sierra Leone< and >West Africa<, Nigeria.
Distribution
>Restricted to West Africa, Niger basin with Upper Niger, Benue, and Niger Delta, most West African coastal river basins from Senegal and Gambia to Tano and Prah basins of Ghana, east of the Niger delta in Cross and Sanaga basins. It has not (or not yet ?) been found in the Volta basin and coastal basins of Togo and Benin, the Chad basin and the basins of the Ogowe, Kwilu-Niari and Chiloango of Tropical West Africa.<