The western side of the Rio Paraná in Brazilian territory has been studied for several years by the Nupélia (Center for Research in Limnology, Ichthyology, and Aquaculture) of the State University of Maringá (Vazzoler et al., 1997). These studies revealed that the floodplain contains a high biological diversity and that it is of fundamental importance for the maintenance of viable populations of species already eliminated in the upper stretches of that basin, especially with regard to large-sized fishes that undertake extensive reproductive migrations (Agostinho and Zalewski, 1996). However, the contribution and/or importance of small lotic environments to these populations are not well known so far. The present study extended these investigations to the eastern bank, treating small lotic bodies of water. The Rio Paraná eastern bank is elevated in the region, so that only the lower parts of the affluents are influenced by the hydrological regime of the river. The ichthyofauna distribution along of two streams was determined, analyzing the spatial and temporal aspects and comparing one to another and, as far as possible, with data from the Rio Paraná itself.