Characidae The largest characiform family, characids are abundant in several environments throughout the Neotropical region. Because of their heterogeneous nature, the species are arranged in several subfamilies in addition to many genera incertae sedis, following Lima et al. (2003). In the present study, the characids are presented jointly. Roeboides descalvadensis, currently considered a seniorsynonym of R. paranensis, is widespread in the Amazônia and Paraná-Paraguay basins (Lucena, 2007). Its recent occurrence in the upper rio Paraná basin is due to the flooding of Sete Quedas Falls by Itaipu Reservoir, as can be evidenced by examination of the very extensive analysis material provided by Lucena (2007) when studying that species. The single lot from the upper rio Paraná basin in that list was caught in 2000, almost two decades after Itaipu Dam’s closure. Today, R. descalvadensis is easily found in the upper rio Paraná. The Coleção Ictiológica do Nupélia (NUP) has 15 lots of the species sampled in the upper rio Paraná, and all of them come from different periods after Itaipu. The only native piranha to the upper rio Paraná is Serrasalmus maculatus, until recently named S. spilopleura, according to Jégu & Santos (2001). After the impoundment, the congener S. marginatus successfully colonized the upper rio Paraná basin and drastically affected the native species population in that region.Agostinho & Júlio Jr.(2002), analyzing data from 21 sampling sites in the region of influence of Itaipu Reservoir and in the upper rio Paraná floodplain, detected an increase in the population of S. marginatus to the detriment of populations of the native species (S. maculatus). Notwithstanding its small size, S. marginatus is gregarious and more aggressive, attacking animals and even humans when taking care of nests or offspring, which explains its colonization success. The current prevalence of S. marginatus has caused a misunderstanding about its origin, considering that it was stated as native by Langeani et al. (2007).

Published as part of Júnior, Horácio Ferreira Júlio, Tós, Claudenice Dei, Agostinho, Ângelo Antonio & Pavanelli, Carla Simone, 2009, A massive invasion of fish species after eliminating a natural barrier in the upper rio Paraná basin, pp. 709-718 in Neotropical Ichthyology 7 (4) on pages 711-712, DOI: 10.1590/S1679-62252009000400021, http://zenodo.org/record/15983883