The distribution and relative abundance of stream fishes in the upper Manyame River, Zimbabwe, in relation to land use, pollution and exotic predators

A survey of the upper Manyame River catchment, middle Zambezi system, Zimbabwe, yielded a total of 22 fish species from 48 stations. The most widespread species (present at >20 stations) were Marcusenius macrolepidotus, Barbus paludinosus, Labeo cylindricus, Clarias gariepinus and Tilapia sparrmanii. The most numerous species (>10% of the total) were B. paludinosus, B. lineomaculatus and T. sparrmanii. A number of species that occurred, or formerly occurred, in the catchment were not collected and the possible reasons for their absence are discussed. Some distinctive patterns of distribution could be discerned, with the presence of exotic predators (Micropterus salmoides and Serranochromis robustus) and pollution being the most important determinants. Although the species richness of indigenous fishes was relatively high when the predators were present, their relative abundance was low. Pollution from sewage, in contrast, brought about a reduction in both species richness and biomass. Land use also influenced both species richness and abundance, which were lower on commercial farms where most streams were regulated by dams and where exotic predators were present. In contrast, both variables were highest on communal lands where subsistence farmers had not built dams, leaving the streams unregulated, and where exotic predators were generally absent.