An inter-basin transfer scheme (IBT) acted as a pathway for several fish species from the Orange River system to enter the Great Fish and Sundays River systems. Of these, Labeo umbratus was found naturally in the Great Fish and Sundays River systems before the inter-basin transfer. Apart from conservation concerns about the introgression of potentially unique genetic lineages of this species, a phylogeographic investigation will offer an opportunity to test biogeographic hypotheses on the evolution and connection between the abovementioned river systems. Labeo capensis on the other hand used to be found only in the Orange River system. The two species are reported to hybridize in Hardap Dam (Namibia), but not in the rest of Orange River system, probably because they utilize different habitats for breeding. The introduction of L. capensis in Great Fish and Sundays River systems may lead to hybridization because of modified habitats and because the natural L. umbratus population have not been in contact with L. capensis until the inter-basin transfer occurred. The aims of this study are to identify and map the distribution of Labeo umbratus genetic lineages, assess which evolutionary processes has been responsible for genetic diversity patterns, relate the population history to known climatic and geological events, assess the level of introgression between L. umbratus populations from different river systems and with L. capensis, and make recommendations to conservation authorities on how to best manage the genetic diversity of L. umbratus and L. capensis in relation to existing inter-basin transfer schemes.

Our research is funded by the National Research Foundation (South Africa)