A new public aquarium in Kirstenbosch National Botanical Garden features several freshwater fish of the Berg and the Breede rivers, two vital water-supply systems for the region. In addition, the existing water feature next to the succulent section of the garden’s Conservatory is now stocked with Cape kurper. The aim is to promote appreciation and awareness of the unique and threatened freshwater fish of the Cape Floristic Region (CFR).
This biodiversity hotspot, known for its floral richness and beauty, also has a remarkable assemblage of aquatic species found nowhere else in the world. In a comprehensive analysis of the CFR’s aquatic biodiversity in 2013, it was noted that 86% of aquatic plants, 72% of crustaceans, 69% of frogs, 89% of caddis flies and 86% of primary freshwater fish were found only here. These are similar levels of endemicity to the area’s terrestrial plants, and in some cases actually surpass them.
The aquatic species inhabit a distinctive environment recognised as one of the aquatic eco-regions of the world. The indigenous freshwater fish of the CFR comprise four fish families and 22 described species and the family Cyprinidae are dominant with 18 species. This family includes the well-known Clanwilliam yellowfish, the Berg-Breede whitefish and the redfin group Pseudobarbus, which is a beautiful but threatened group of small river fish. Other fish families are the Galaxiidae (represented by the Cape galaxias), Austroglanididae (rock catfish – two species) and the Anabantidae (represented by the Cape kurper).
More than half of the indigenous freshwater fish of the CFR are listed as threatened. These fish have evolved in clear, unpolluted rivers with varied habitat, and no fish-eating fish. The indigenous fish have not coped well with predatory invasive fish such as bass, trout and bluegill sunfish, and the degraded rivers that are found in the heavily farmed and urbanised areas of the region. Their strongest populations are in ecologically healthy streams and rivers with good habitat and water quality, and near natural flow with no invasive fish.
The focus of the 1.2 metre-long public aquarium is on fish that occur in rivers within 100km of Kirstenbosch. This includes the Berg-Breede whitefish, a large endangered cyprinid that was once abundant and widespread in the Berg- and Breede river systems. The only inland water where it is currently abundant is Brandvlei Dam near Worcester. The aquarium also features the Breede River redfin (Pseudobarbus sp. burchelli breede) that is widespread and common in ecologically healthy mountain streams in the Breede River catchment. The third species in the aquarium is Cape kurper, widely found in ecologically healthy rivers and streams across the CFR.
Until a few years ago, the water feature in the succulent section of the Botanical Society Conservatory at Kirstenbosch had otjikoto tilapia (Tilapia guinasana), a fish found in Lake Guinas in Namibia. CapeNature and Kirstenbosch management agreed it was time to update the display and replace the Namibian tilapia with Cape kurper.
The Cape kurper has settled in well and will hopefully breed soon. There is also a healthy natural population of Cape galaxias in the Upper Liesbeek River that flows through the gardens. –
Written by Dean Impson and Elton le Roux. Impson is a senior ecologist at CapeNature, and Le Roux is estate manager at Kirstenbosch.
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