A massive invasion of fish species after eliminating a natural barrier in the upper rio Parana basin

Based on long-term studies in the upper rio Parana basin, in addition to a broad review of literature and other information, we were able to identify 33 species of native fishes in the lower rio Parana basin that successfully colonized the upper rio Parana after Itaipu impoundment, that flooded the natural geographic barrier constituted by the Sete Quedas Falls. These species belong to six Orders, encompassing two of Myliobatiformes, six of Characiformes, 17 of Siluriformes, six of Gymnotiformes, one of Perciformes, and one of Pleuronectiformes. Extensive remarks regarding each species, including their influence upon the native assemblage, in addition to comments on other non-indigenous species, are also provided. We conclude that, in spite of its widespread neglected by environmental impact studies, massive invasion of species is a real possibility when natural barriers are suppressed by reservoirs.