Fish assemblages

Abstract

The part of the upper Paraná River basin between the mouth of the Paranapanema River and the Itaipu Reservoir includes at least 153 fish species, recorded in several surveys carried out during fifteen years (1986-1987; 1987-1988; 1992-1993; 1993-1994; 1994-1995; 2000 and 2001). Characiformes and Siluriformes dominate the fish fauna contributing 77% of the total number of species. Native species of the Upper Paraná River floodplain contribute 75.6% of the total number of species. Introduced species from other basins represent 8.4% of the total, whereas the ones dispersed into the Upper Paraná River after the formation of the Itaipu Reservoir, that removed the natural barrier of the Salto de Sete Quedas, represent 15.8 %. Several habitats were sampled and rivers differed relative to fish assemblage from streams and lagoons, which could be attributed to the higher occurrence of small sized species typical of the latter environments. River and channels generally have higher species richness than lagoons. The number of species in a particular combination of month and site (local species richness) varied from 3 to 37. Most common values for richness were 12, 18 and 22 species, indicating a high temporal and spatial species turnover. Most of the spatial variation in the Upper Paraná River floodplain was dependent on the type of environment sampled. Indicator species analysis identified 56 out of 100 species that had significant indicator values: 36 species were typical of rivers, 15 were typical of lagoons, and six were indicators of channels. A lower level of fish assemblage stability was noted in the Paraná River channel, related to the higher degree of hydrological regulation promoted by the dams located upstream.