Comprehensive DescriptionRead full entry
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.