The African weakly electric fish, <i>Gnathonemus petersii</i> (Günther, 1862) (Osteoglossiformes: Mormyridae): a first morphometric exploration into a hidden species complex

Abstract A morphological study of populations identified as Gnathonemus petersii, a widespread mormyrid species distributed from the Niger to the Congo Basin, revealed it to be a species complex. Its junior synonyms, Gnathonemus brevicaudatus and Gnathonemus histrio, collectively represent a distinct valid species, G. brevicaudatus. Gnathonemus brevicaudatus differs from G. petersii by a longer caudal peduncle and a shorter anal fin. In addition, a new species, Gnathonemus marqueti sp. nov., from the Upper Kotto Basin, a right bank affluent of the Ubangi River in the Middle Congo Basin, is described. Gnathonemus marqueti differs from Gnathonemus barbatus and Gnathonemus echidnorhynchus by its higher and lower number of lateral line scales, respectively, from G. brevicaudatus and G. petersii by its lower number of dorsal fin rays, and from Gnathonemus longibarbis by its shallower caudal peduncle and narrower head. Furthermore, specimens from the Upper Lualaba, Kasai, and Lowa basins were found to belong to three potentially new species, in need of further taxonomic study. Thus, the supposedly widespread species, G. petersii, was found to contain hidden species diversity represented at least by the new species and G. brevicaudatus, whose allopatric ranges are restricted. These findings highlight the importance of appropriate freshwater conservation initiatives within the Congo Basin.