Isichthys henryi Gill, 1863

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Possesses electroreceptors over the entire head, the dorsal region and some parts of the ventral region; absent from the side and the caudal peduncle where the electric organ is located. Electric organ discharge (EOD) rates are of low frequency and sexually dimorphic as to waveform (Ref. 10011).

Body very elongate, body depth 5.9-11.9% SL; cross-section slightly compressed laterally, about 70% as wide as deep. Unpaired fins long, dorsal base, 44-48% SL originating well in advance of anal. Anal base, 39-41% SL. Teeth large and bicuspid, five (rarely six) in upper jaw, six in lower. Head 1.75-2 times as long as deep. Snout bluntly rounded, 21-25% HL, mouth subterminal, opening directly below posterior nostril. Submental swelling present, but reduced, covered with electroreceptors. Four large Knollenorgan electroreceptors, with pore diameters equal to the posterior nostril, surround the eye. Eye small, less than 50% of snout length. Dorsal fin with 42-49 rays in rivers of Nigeria to the Ogowe (compared to 37-44 in the Upper Guinea populations). Anal fin with 40-48 rays in the populations from Niger to Ogowe compared to 36-44 for Upper Guinea. Caudal peduncle very small, its length only 8% SL; 1.7-3.3 times as long as high. Caudal fin small with obtusely pointed lobes. 120-140 scales in the lateral line with clinal variation from 135-145 in Upper Guinea to 120-130 in Lower Guinea; 16-20 circumpeduncular scales (circumpeduncular scales in Isichthys are sometimes irregular in shape and arrangement, leading to variable counts depending on where the counts are taken). Maximum size: 235 mm SL.

Coloration: uniformly dark chocolate-brown, yellow-brown on the head. Fin rays dark brown, membranes transparent.

This species is known from Guinea, Sierra Leone and Liberia, and then from Nigeria to the Democratic Republic of Congo.

Central Africa: Isichthys henryi is distributed throughout Lower Guinea, including the Cross River of Nigeria/Cameroon (Kadem Toham and Teugels 1998), the Sanaga, the Kribi, the Ntem, the Ogowe, the Ivindo, the coastal streams around Mayumba, and in the coastal drainages in Congo, including the Kouilou.

Western Africa: It is found in West Africa from the coastal basins of Guinea, Sierra Leone and Liberia, and from Ogun as well as from coastal reaches of rivers in Western Nigeria and the Lower Niger.