Genetic differentiation among populations of <em>Pseudoplatystoma corruscans</em> (Agassiz, 1829) (Osteichthyes, Pimelodidae) isolated by the Guaíra Falls in the Paraná River

Abstract

Until 1982, the Guaíra Falls, also named the Seven Falls, constituted a barrier to the dispersion of migratory fish in the Paraná River. The objective of this work was to verify if populations of Pseudoplatystoma corruscans (Osteichthyes, Pimelodidae) were isolated by the Guaíra Falls. Samples from the Upper Paraná River floodplain (PL), the Itaipu reservoir (IT), and downstream Yacyretá reservoir (YA) were compared by RAPD markers. Lynch's F_ST was significant between PL and IT (0.090), and PL and YA (0.112). Estimated gene flow (Nm) varied from 2.0 between PL and YA to 8.1 between IT and YA. Nei's genetic distance varied from D = 0.0638 between PL and YA to D = 0.0174 between IT and YA. These results indicate the existence of genetic differentiation and that, possibly, the Guaíra Falls isolated the populations reproductively. They also suggest the possibility of different spawning areas, partially avoiding the genetic homogenization of the IT and PL populations.