Ongoing efforts to safeguard the Critically Endangered Tradouw redfin through monitoring

The Critically Endangered Tradouw redfin (Pseudobarbus burchelli) is one of South Africa’s most range-restricted freshwater fishes. It is endemic to the Huis–Tradouw River catchment near Barrydale in the Western Cape. The species is listed as Critically Endangered due to its small and fragmented distribution, threats from invasive fish species, pollution, water abstraction, and habitat degradation. Historically the redfin occurred throughout the Tradouw catchment and annual monitoring was initiated in 2012. Data from the monitoring shows that the redfin is experiencing ongoing range decline and that the population in the Tradouw River has dropped to below detectable levels. The remaining stronghold for this species is in the Huis River tributary of the Tradouw River.

Monitoring data shows that redfin abundance in the upper Huis River is relatively stable and the population comprises several size/age classes. The upper Huis River is also free of any invasive fish and the only impact here is water abstraction for both agricultural and residential use. In contrast, the lower Huis River is severely impacted by anthropogenic activities, and the habitat was in very poor condition at the time of the 2026 sampling event. While the redfins persist in this section of river, they co-exist with invasive banded tilapia (Tilapia sparrmanii). Relative abundance of redfins compared to the banded tilapia is very variable over time and during the 2026 survey redfins comprised just over 10% of all fish caught. Both redfins and banded tilapia had very high ectoparasite loads. The poor water quality and lack of flow is suspected to be one of the drivers of the infection as these parasites were not observed on redfins from the upper Huis River. The parasitology research group at North-West University (NWU) is presently conducting a study on this.

While the upper Huis River sub-population is stable, it is very small, persisting in less than 1km of river, and is highly susceptible to threats. In order to secure the long-term survival of the Tradouw redfin, water use patterns in the greater Huis River catchment must be addressed in order to allow for maintaining environmental flow releases and managing the river to ensure adequate habitat quality for the redfin. In addition, the proposed redfin conservation translocation into suitable habitat in the upper Huis River must be prioritised for implementation, pending the outcome of a risk assessment.