Xenomystus nigri (Günther, 1868)
Species overview
Body shape a knife fish with convex back and slightly convex underside of body along base of anal fin. Dorsal fin absent, pelvic fins very small. No colour pattern or distinctive marks in adults. Olive brown or brown, anal fin somewhat leighter.
Size observed: Smallest of all Old World freshwater knifefishes, attains about 20 cm total length.
Taxonomic description
-Body strongly laterally compressed, greatest depth above origin of anal fin.
-Head short, upper profile straight, or feebly concave, continuing into the convex outline of back.
-Underside of head straight, gular region convex, merging in sligthly convex unterside of body - base of anal fin.
-Mouth terminal, its edge slightly anterior to posterior rim of eye.
-Outer edge of mandible with well developed serrations.
-Opercular cleft long, round; no more than 3 branchiostegal rays; gill rakers rudimentary.
-Base of pectoral fin on level of edge of mouth, fin extends well behind origin of anal fin.
-Pelvic fins small, with only 3-4 fin-rays.
-Dorsal fin absent.
-Anal fin very long, 94-111 fin rays, merging in caudal fin, 7-9 fin-rays, without apparent border. 67-73 vertebrae.
-Coloration, uniformly brown or olive brown, the anal fin appears a little lighter because of its transparent membrane.
Type locality
N. nigri : "River Niger",
N. (Xenomystus) nili : "Nil, Bahr el Saraf und Bahr el Gebel."
Distribution
"... widely distributed in tropical Africa, in the Nile, Chad, Niger, Ogowe and Congo basins. It is known from coastal river basins in Sierra Leone, Liberia, Togo Benin and Cameroun. It has not been found in Côte d'Ivoire or Ghana. In the Niger basin it occurs in the Benue and Niger delta but not in the Upper Niger. In the Congo basin it ocurs mainly in the Cuvette Centrale and Ubangui."