Revalidation of Enteromius karkensis (Gilchrist and Thompson 1913) (Cypriniformes: Smiliogastrinae) from the southern temperate freshwater ecoregion, South Africa

The chubbyhead barbs, a distinct group of fishes endemic to southern Africa, currently include eight valid species. Historically, Enteromius anoplus was the most widespread freshwater fish in South Africa due to synonymizations in the 1960s. It occurred in nearly every river system except coastal systems in the Cape Fold Ecoregion and the lower Orange River. However, a recent revision utilizing molecular and morphological analyses has led to significant taxonomic updates. Enteromius anoplus is restricted to the Gouritz River system, whereas Enteromius cernuus and Enteromius oraniensis have been revalidated and respectively confined to the Olifants and Orange River systems. Additionally, a new species Enteromius mandelai was described, with its range currently considered to encompass several river systems in the Eastern Cape. Despite these advances, the taxonomic status of fish previously assigned to E. anoplus from KwaZulu-Natal remained uncertain. In this study, an integrative approach, combining genetic analysis, morphological characteristics, and geographic data, was employed to resurrect Enteromius karkensis as a distinct species from E. anoplus. Enteromius karkensis is deeply genetically differentiated (3.99%-8.07% p-distance) from its congeners within the chubbyhead group. Morphologically, E. karkensis is easily distinguishable from its counterparts due to possession of a terminal mouth (vs. inferior in E. amatolicus), one pair of maxillary barbels (vs. two conspicuous pairs in E. motebensis, E. treurensis, and E. gurneyi), and a complete lateral line (vs. incomplete in E. anoplus and E. oraniensis). Furthermore, E. karkensis is differentiated from E. mandelai and E. cernuus by its long maxillary barbels that extend beyond the midpoint of the orbit. These findings highlight a consistent pattern from previous studies that show many freshwater fishes in South Africa have narrow geographic ranges. This emphasizes the importance of targeted conservation and management efforts, and our understanding of the biogeographic and evolutionary history of freshwater fishes in southern Africa.