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In this study we conducted an ichthyofaunistic survey in the Pirapó River drainage, upper Paraná River basin, based on voucher specimens deposited in the Coleção Ictiológica do Nupélia/UEM. We reported a total of six orders, 23 families, and 76 species, in which four of them were classified as allochthonous and two as exotics. Twenty-eight percent of these species were recorded only for tributaries, whereas the commercially important migratory species, Dourado - Salminus brasiliensis (Cuvier, 1816), was recorded in the main channel, indicating that the Pirapó River, still free from impoundments, may be one of the last rivers in the upper Paraná River basin that can be used to protect migratory fish species.

Aim: This study uses the abundance of fish eggs and larvae to evaluate the importance of the main channel of the Paraná River and the adjacent areas of the floodplain, in the last dam-free stretch in the Brazilian territory, for the spawning and development of fish of different reproductive guilds, in order to obtain subsidies to assist in the management and conservation policies of this area, focusing on the maintenance of dam-free areas. Methods: Data were taken quarterly from August 2013 to May 2015, in 25 sites, grouped into three biotopes: main channel, tributaries and lagoons. Possible spatial variations in fish spawning and development as well as composition and structure of larvae were evaluated. Results: Higher densities of eggs were found in tributaries (Paracaí and Amambai rivers) and greater densities of larvae were observed in lagoons (Saraiva). Significant differences in composition and structure of larvae were detected only between sampling stations. As for taxonomic composition, 29 taxa were recorded, mostly non-migratory. However, long-distance migratory were also widely distributed, such as Brycon orbignyanus, Pseudoplatystoma corruscans, Prochilodus lineatus, Piaractus mesopotamicus and Rhaphiodon vulpinus, as well as invasive species Platanichthys platana and Hemiodus orthonops. In turn, Salminus brasiliensis presented low occurrence. Conclusions: This study evidenced that different species spawn in the region, mainly in tributaries, and their eggs and larvae are transported to the main channel of the Paraná River and adjacent lagoons, to complete their early development. The capture of larvae of important migratory species suggests that this environment still exhibits suitable conditions for their reproduction, mainly due to the presence of dam-free tributaries. Also, they emphasize the importance of the integrity of these environments for the maintenance of the regional fish fauna, and it is extremely important the monitoring of reproduction of the most endangered species, as well as of invasive species.

The Corumbá Reservoir is located in Corumbá River, a tributary to the right bank of Paranaíba River, upper Paraná River basin. Fish were collected monthly, from March 1996 to February 2000, in 17 sampling stations along Corumbá Reservoir and its influence area, using gill nets, casting nets, electrofishing and long lines. Considering the entire period, 119 fish species were colleted, which belong to seven Orders, 26 Families, and 78 Genera. Among them, five species are considered endemic to Corumbá River basin, and 17 are probably new to the science.