For fisheries enhancement purposes, nonnative species have been introduced into waters across the world. Subsequent consequences for food web composition were often unforeseen, as exemplified by the case of Lake Victoria. Here, introduction of the nile tilapia and nile perch brought species rich communities of native cichlid fish to extinction, but subsequent overfishing of these target species may well have led to recovery of some of these native species. In highly eutrophic lakes purposeful alterations of this community involve increases in piscivorous predators and decreases in benthivores and planktivores. The reduced predation on zooplankton and reduced sediment resuspension have led to drastic reductions in turbidity, and clear water (Secchi disk transparency >1m) is an important target for lake management.
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