Freshwater fishes of the Waterberg aquatic ecoregion, South Africa: Diversity, taxonomic conflicts and conservation concerns

Southern Africa is a region denoted by both high levels of fish diversity, some of it cryptic and unrecognised by current taxonomy, and severely threatened freshwater ecosystems. The Waterberg, a key aquatic ecoregion of the greater Limpopo River basin in South Africa, represents an area with high terrestrial conservation value but is lacking in aquatic biodiversity information. This study characterised this unique aquatic ecoregion's fish diversity, their biogeographic patterns and threats to this biodiversity. A total of 29 fish species (11 families, 19 genera) were identified, with many distinct upland fish communities occurring within the high-altitude headwaters of the ecoregion, whereas lowland fish communities tended to be more homogeneous. Mitochondrial CO1 barcoding revealed genetically distinct lineages in four presumed-widespread southern African species: the shortfin barb, Enteromius brevipinnis (Jubb, 1966); hyphen barb, Enteromius bifrenatus (Fowler, 1935); straightfin barb, Enteromius paludinosus (Peters, 1852) and snake catfish, Clarias theodorae Weber, 1897, that were restricted to the Waterberg aquatic ecoregion. The level of genetic divergence suggests that these four Waterberg-restricted lineages are likely new candidate species. These findings indicate the Waterberg to be a biogeographic island within the greater Zambezian ichthyofaunal region of southern Africa, which should be prioritised for aquatic ecosystem conservation. Current terrestrial conservation structures in the region, encapsulated within the Waterberg Biosphere Reserve, appear to protect this distinct ichthyofauna from human land-use-derived impacts. Nonetheless, the presence of the invasive predatory largemouth bass (Micropterus nigricans) inside the biosphere represents a credible conservation threat. Engagement with biosphere stakeholders will be critical for managing this threat to the Waterberg's unique ichthyofauna going forward.