Genetic Structure and Conservation Strategies for the Endangered Catfish Steindachneridion melanodermatum (Siluriformes, Pimelodidae) in the Iguaçu River, Brazil

The endemic catfish Steindachneridion melanodermatum from the Iguaçu River basin, southern Brazil, is one of the most threatened pimelodid species. Comprehension of its genetic structure is imperative to the formulation of long‐term efficacious conservation strategies. A genetic analysis was conducted on three populations from the lower Iguaçu River: two downstream of the Baixo Iguaçu Hydropower Plant (Sites 1 and 2) and one (Site 3) corresponding to fishes collected upstream of the Iguaçu Hydropower Plant approximately 30 years before and maintained by COPEL (energy distribution company of Parana State) for breeding stock programs. These were used microsatellite markers to assess genetic diversity, detect potential bottlenecks and estimate relatedness. The findings of this study indicated the presence of two discrete management units (MUs): a downstream unit consisting of Sites 1 and 2 and an upstream unit comprising Site 3. The observed genetic differentiation indicates the role of river fragmentation in shaping the population structure of S. melanodermatum . We recommend targeted conservation actions, including separate management of downstream and upstream populations of the Baixo Iguaçu Hydropower Plant, to preserve the genetic integrity of this endangered and endemic species within the unique ecosystem of the Iguaçu River.