Abstract
SUMMARY Fish population changes in the Hendrik Verwoerd Dam are presented as sampled with a series of multifilament gill nets from Spring 1971 to Summer 1977. During this period, species such as Barbus halubi (smallmouth yellowfish), B. kimberleyensis (largemouth yellowfish), Labeo capensis (Orange River labeo), Cyprinus carpio (common carp) and Clarias gariepinus (sharptooth catfish) appeared to favour the newly created dam-environment. L. umbratus (moggel), however, showed a slight decline in abundance, while the Orange River rock catfish, Gephyroglanis sclateri, disappeared entirely from the gill net catches four years after inundation. Low numbers of Labeo umbratus x L. capensis hybrids were sampled, mainly in areas where small streams enter the dam. Rainbow trout (Salmo gairdnerii) and brown trout (S. trutta) were netted annually during the early summer months. Fluctuations in water level and siltation are probably the main factors causing continual changes in food supply and juvenile production and,...
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