Evidence for the unexpected dispersal of Leporinus tigrinus Borodin, 1929 through hydroelectric dams in the most regulated Neotropical river basin

The Upper Parana River Basin (UPRB) is harmed by several human activities, among which species introduction is particularly intense, making it the Neotropical ecoregion with the highest number of non-native fish species. Leporinus tigrinus Borodin, 1929 is a native species of the Tocantins-Araguaia River Basin and was recorded for the first time in the UPRB in 1999. Since then, the species was progressively recorded in lower portions of the UPRB (downstream Corumba River). Therefore, the aim of this study was to provide evidence of possible introduction, establishment and dispersion of the species in that region. For this purpose, an inventory of its occurrence was performed by sampling ichthyoplankton, juveniles and adults of fishes in tributaries of the Porto Primavera Reservoir, as well as by compiling data from scientific collections considering all the UPRB. Diet and reproductive aspects were also analyzed. Overall, 23 specimens of L. tigrinus (10 adults and 13 juveniles) and five eggs (identified by DNA Barcoding) were sampled, evidencing the occurrence, reproduction, and recruitment of this species in the basin. The results of this study support the conclusion that L. tigrinus is an introduced species in the lower portion of the UPRB, capable of dispersing over long distances by passing through several reservoirs and dams (from upstream to downstream), possibly via turbines, spillways, locks, and fishways. Its dispersal pathway differs from the patterns observed for most invasive fish species in this basin, and suggests a substantial downstream dispersion through dams, even in the absence of fishways.