| Summary: | The aim of this study was to analyze the structure of ichthyoplankton in two places in the Parana river upstream the Yacyretá dam during three phases in the waterline filling. Data comes from fortnight collections in two stations for active filtering network 100 m3 with 500 microns and fixed with 4% formaldehyde. In the reservoir, 6 orders and 17 species were recognized, while in the sub damp 7 orders and 35 species were recognized. The most abundant species were Bryconamericus stramineus and Plagioscion ternetzi in the sub damp and Lycengraulis grossidens and Prochilodus lineatus in the reservoir. Preflexion stage was the most frequent in both places. Statistical analysis of the differences in terms of richness and abundance showed significant variations just between reproductive cycles, not between levels. Spawning and growth of early ontogenetic stages zones and feeding and growth zones were recognized for different species with high reproductive success in modified environments.
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