For a long but uncertain span of evolutionary history, a small freshwater fish species has been slowly evolving – nameless and unknown – in the rivers at Africa’s southernmost tip. Now, at last, the only redfin living there not only has a name but has been formally described.
The redfins that occur in the Heuningnes River system, including the Nuwejaars River and its many tributaries, have now been officially named Pseudobarbus agulhas (Agulhas redfin). Scientists had already discovered that these fish formed their own distinct lineage, but until recently they were only referred to informally as the Heuningnes redfin (Pseudobarbus sp. ‘Heuningnes’).
The species’ official recognition comes through a recently published scientific paper, Systematic review of Pseudobarbus burchelli with revalidation of P. vulneratus and description of a new species, authored by Dr Fatah Zarei, Dr Melissa Martin, Prof Paul Skelton and Prof Albert Chakona, all from the NRF-South African Institute for Aquatic Biodiversity (NRF-SAIAB).
Our Endangered redfin
The authors explain that the name Pseudobarbus agulhas reflects “the region’s distinct biogeographic boundary and ecological significance, which supports a rich diversity of both marine and freshwater species”.
But the name also draws attention to the very limited distribution of the species – and therefore its conservation status: Endangered. The Agulhas redfin faces serious threats from invasive alien fish such as bass and bluegill, which compete with or prey on them.
This species adds to a growing list of discoveries: there are now 15 recognised redfin species, compared to only seven in 2001. The Agulhas redfin is a species with two sub-lineages – one in the Heuningnes River system, believed to be the species’ evolutionary stronghold, and a second in the Karingmelks River, which is in the Klein River system.
The hidden history of the Agulhas redfin
Along the southern coast of South Africa, these rivers tell us a story of survival, isolation and adaptation. The Agulhas redfin belongs to a group of closely related species known as the Pseudobarbus burchelli complex, which also includes P. burchelli and P. vulneratus. The evolutionary split within this group is remarkable: P. burchelli in the Tradouw catchment of the Breede River system diverged from the ancestral population of the other two species nearly 1.7 million years ago, during a time when high sea levels fragmented rivers and isolated freshwater populations.
The ancestral population, which later gave rise to P. vulneratus and P. agulhas, spread across several river systems – the Breede, Duiwenhoks, Goukou and Heuningnes – sometimes aided by natural events like river captures. Genetic studies show that P. vulneratus and its close relative P. agulhas then split apart about 800,000 years ago, well before the last glacial period. The populations that remained in the Breede, Duiwenhoks and Goukou rivers eventually evolved into P. vulneratus, while the population that colonised the Heuningnes River became P. agulhas.
A species shaped by isolation
The Agulhas redfin has remained largely isolated in the Heuningnes system, where unique environmental conditions have shaped its evolution. The river is more turbid, has higher conductivity and flows with gentler gradients compared to neighbouring systems – factors that likely reinforced the separation of this species and allowed it to follow its own distinct evolutionary path. A relatively recent river capture likely linked the Heuningnes and Klein rivers, enabling the Agulhas redfin to naturally colonise the upper reaches of the Karingmelks River in the Klein system.
Morphology, habitat & biology
Today, the Agulhas redfin is known to differ significantly, genetically, from its closest redfin relatives: Pseudobarbus burchelli and Pseudobarbus vulneratus, found in the Breede River system. It is one of only six redfin species with double barbels on its face. Its body is olive-brown above the lateral line, darkening toward the dorsal region. And below the lateral line, the colour transitions to blemished silvery-white, and then to white below its body. The base of its fins is bright scarlet – hence its name. It differs from its closest relatives in the Breede River system in head shape and the structure of the teeth at the back of its throat.
It occurs in pools and streams in the Heuningnes and Klein River systems – the only redfin species in this region. As omnivores, they feed on algae and small invertebrates. Breeding occurs in summer, with spawning taking place in riffles above the pools.
Now that the Agulhas redfin has been named and described, the next step is to protect the species.
The authors emphasise that the long-term isolation that shaped the evolution of P. burchelli, P. vulneratus, and P. agulhas must be preserved to allow these species to continue their unique evolutionary paths. This can be ensured by preserving their geographic isolation and safeguarding the unique habitats where they live.
They also recommend separate management plans for each of the two sub-lineages of P. agulhas, reflecting the different environments they inhabit and the unique threats each faces.
Protecting redfins in the Nuwejaars
The Nuwejaars River Nature Reserve, the non-profit company managing the Nuwejaars Wetlands Special Management Area (NWSMA), is dedicated to protecting our freshwater fish species – in particular the Agulhas redfin and Galaxias sp. ‘Heuningnes’ – both endemic to this region.
With support from the Mohamed bin Zayed Species Conservation Fund, and with the necessary CapeNature permits, redfin individuals have been relocated from various sites to two fish sanctuaries. In these safe environments, free from threats such as invasive fish, they are expected to breed successfully.
Eventually, the fish will be reintroduced to conserved areas within their historical range along the Nuwejaars River and its tributaries, including pools and streams where they will remain protected. But safeguarding freshwater fish – the second-most threatened group of animals in South Africa, after sharks – is both challenging and costly. Experts from the South African National Biodiversity Institute (SANBI) estimate that recovering and protecting 30 of country’s most threatened freshwater fish species will require R168 million over the next five years, compared with just R18 million spent in the previous five years.
A long-term project
NRNR Conservation Manager Erica Brink says, “Protecting Agulhas redfins is our long-term commitment to the species. It will take many years and considerable resources to protect our freshwater fish species. But we’re in this for the long haul. Redfins are a flagship species for the Nuwejaars Wetlands – and it’s our responsibility to ensure their survival.”
Our sincere thanks to Mohamed bin Zayed Species Conservation Fund for the support over the past year.
