Pronothobranchius is a species group that is ill defined, but according to an article in the Journal of the AKA, it is considered valid along with a few other species placed into the same group. Pronothobranchius gambiensis was long a sought after species that was not located and relegated to an ‘unknown’ status.
Svensson G. S. O. 1933 – Fresh water fishes from the Gambia River (British West Africa). Results of the Swedish Expedition 1931. Systema Naturae, Ed. X. v. 12 (no. 3): 1-102