Pimelodidae

Pimelodid, as currently defined, presents several modifications if compared to the traditionally accepted definition until late in the last century (Lundberg & Littmann, 2003). In any case, it encompasses species with a broad range of sizes, and several species are especially important as human food resources. Hypophthalmus edentatus, a zooplanktivorous species, was previously distributed only in the lower Paraná and Amazon basins. In the early years after the Itaipu Reservoir was completed, this species was one of the most abundant, benefitting from the upsurge of organic matter and increasing zooplankton and phytoplankton biomass (Ambrósio et al., 2001; Abujanra & Agostinho, 2002). Lundberg & Littmann (2003) reported only H. oremaculatus for the rio Paraná basin, but Graça & Pavanelli (2007), comparing dispersed individuals with the original description of this species, observed that the characteristics did not match. In addition, Britski et al. (2007) referred only to H. edentatus for the Pantanal (Paraguay River basin).

Pimelodus ornatus, a species with a color pattern quite different from other species of the genus, was restricted to the Paraguay and Paraná Rivers downstream from Sete Quedas Falls and has been caught in the upper rio Paraná basin since the Itaipu impoundment (Graça & Pavanelli, 2007). In the floodplain stretch, it preferentially inhabits rapids.

Sorubim lima is another pimelodid species that apparently colonized the upper rio Paraná basin, where it was absent before Itaipu’s closure as suggested by Langeani et al. (2007), who listed it as being of unknown origin in the upper rio Paraná basin. Corroborating this, in the recent revision of the genus Sorubim, Littman (2007) provides a list composed of more than 80 lots of material examined for that species, but none from the upper Paraná.