Variations in the endemic fish assemblage of a global freshwater ecoregion: Associations with introduced species in cascading reservoirs

The present study aimed at assessing spatial and temporal changes in the composition and structure of an endemic fish assemblage and the possible associations with introduces species in a system of cascading reservoirs, in Iguaçu River, state of Paraná, southern Brazil. We collected 135,639 specimens: 131,716 individuals of endemic species and 3923 of introduced species. The most abundant introduced species were: Odontesthes bonariensis (85.1%), Prochilodus lineatus (7.5%) and Tilapia rendalli (4.9%). Significant spatial and temporal differences in richness were observed for both endemic and introduced species. The composition and structure of the assemblage of endemic and introduced fish exhibited significant spatial differences. The Procrustes analysis showed a significant spatial association between composition and structure of the assemblage of endemic and introduced fish in Iguaçu River. Changes in the endemic fish assemblage of Iguaçu River related to the establishment of introduced species and to habitat changes caused by cascading reservoirs enable advancing knowledge on environmental impacts in freshwater ecoregions.

► Endemic fish assemblages showed a significant spatial association with introduced species in a cascading reservoir system.
► The distributions of endemic and introduced species in a freshwater ecoregion show distinct patterns.
► Spatial changes in endemic fish assemblages are related to the establishment of non-native species.
► Cascading reservoirs create conditions to advance knowledge on environmental impacts of biological invasions.