Niche expansion by indigenous fish species following the introduction of rainbow trout (Oncorhynchus mykiss) in a subtropical river system, upper Blyde River, South Africa

The introduction of alien predatory fish such as rainbow trout ( Oncorhynchus mykiss ) can have a significant effect on indigenous communities altering the structure and dynamics food webs. Quantifying trophic niche utilised by species is therefore important to aid our understanding how their feeding strategies might establishment, define functional role inform potential impacts. This study assessed web interactions between in river reaches that are invaded O. sections free invasions upper Blyde River catchment, South Africa. It specifically evaluated hypothesis invasion likely lead decrease diversity through predation will shift either minimise competition with, or avoid predation, mykiss. Gut content stable isotope analyses were used determine interactions. Fish uninvaded areas fewer similar sources occupied lower levels, than areas. fed mainly invertebrates at levels fishes. suggests current impact for resources. We posit reduced abundance fishes thereby pressure aquatic invertebrates, with knock-on interrelationships among assemblages. Our findings consistent other studies Africa shown impacts decline fragmentation populations shifts.