Fishes from low-order streams in a high-endemism region, lower Iguassu River, Brazil

The Neotropical region has the greatest diversity of freshwater fish in the world. Among the ecoregions proposed for this region, the Iguassu ecoregion is of great importance because its ichthyofauna is characterized by a high degree of endemism. Fish assemblage inventories have contributed to knowledge of species distributions and identification of unknown species. We carried out a fish inventory and an evaluation of their distribution in nine headwater streams in the lower reaches of the Iguassu River basin. For this purpose, the fishes of nine small streams were sampled quarterly from September 2014 to June 2015 using electrofishing equipment. In all, 2,854 fish were recorded for the nine inventoried streams. They belong to six orders, 11 families and 27 species. The highest species richness was recorded for Siluriformes and Characiformes. Characidae was the family with the highest species richness, as well as the most individuals. Psalidodon bifasciatus was the most abundant and common species in all streams. Species richness was generally low, varying among streams. Six non-native species were recorded, among which Oreochromis niloticus and Poecilia reticulata were predominant in the Três Barras and Aparecida streams, respectively. The presence and abundance of these species in streams with reduced species richness, with a high degree of endemism, increases the risk of decline and even extinction of other species. Thus, our results help expand knowledge of the ichthyofauna in a vulnerable region, in the sense of supporting future management measures aimed at preserving communities.