Zamba, A.I.,  Mamonekene, V.,  Vreven, E. & Stiassny, M.L.J. 2013. ‘Xenocharax crassus Pellegrin, 1900 (Characiformes: Distichodontidae) from the Congo River basin, central Africa: in need of revalidation’. Fifth International Conference of the Pan African Fish and Fisheries Association (PAFFA5). Book of abstracts.

Conference abstract

Currently the genus Xenocharax is considered to be monotypic. However, two species have been described, X. spilurus Günther, 1867 from “Gaboon” and X. crassus Pellegrin, 1900 from the Alima River (Congo basin, Republic of the Congo), with the latter synonymised with X. spilurus by Daget in 1960. However, collections from the Congo River in the Democratic Republic of Congo and the Republic of the Congo indicate that Xenocharax specimens from the Congo basin are not readily attributable to X. spilurus, which appears restricted in distribution to the Lower Guinean ichthyofaunal province. The presence of a large black mark on the anterior part of the dorsal-fin (vs. no such mark) and a small black spot on the root of the caudal (vs. large black spot) readily distinguishes them from X. spilurus. These observations led to the assumption that, contrary to the opinion of Daget (1960), X. crassus could be a valid species. To further investigate the taxonomic status of X. crassus, 12 meristics and 20 measurements were taken on 78 specimens of Xenocharax (42 Congo and 36 Lower Guinea respectively), including all available type specimens. In addition, osteological characters, geometric morphometric comparison, and divergence in 3 genes were also investigated. The study revealed that, in addition to colour pattern and body shape differences, X. crassus, endemic to the Congo River basin, is easily distinguished from X. spilurus by its wider mouth (29.6-33.4% vs. 24.5-28.7% HL) and a lower number of supraneurals [5-6 vs. 7-8 (exceptionally 6)]. Numerous non-synonymous base changes in three genetic markers also confirm the distinctiveness of X. crassus. Therefore we conclude that X. crassus should be revalidated.