Numerous nematodes were found in the rectum of three fish species Synodontis ocellifer, S. nigrita and S. schall (Mochokidae, Siluriformes) from the Gambia River and Mare de Simenti, National Park Nikolo Koba, Senegal. A nematode species Raillietnema synodontisi Vassiliades, 1973 (host S. ocellifer), is redescribed using morphometric (including scanning electron microscopy) and molecular characteristics and transfered into the genus Labeonema Puylaert, 1970. It is morphologically and metrically similar to Labeonema intermedium Puylaert, 1970, the other congeneric species (L. bainae Baker, 1982, L. bakeri Van Waerebeke, Chabaud, Bain et Georges, 1988 and L. africanum Moravec et Van As, 2004) differs from them either by the spicule and gubernaculum lengths, distribution and number of pre-cloacal papillae, position of the vulva, as well as hosts and geographical distribution. The partial sequences of small ribosomal subunit rDNA of L. synodontisi was analyzed and compared with other nematodes sequences. Molecular analyses seem to support the position of this nematode species based on the morphological observation.