Longitudinal patterns in distribution of native and non-native fish species in a regulated temperate Neotropical river

Abstract: Aim We evaluated the longitudinal patterns in distribution of native and non-native fish species a hydrologically fragmented environmentally variable lowland temperate river. Methods Four sites representing contrasting habitat environmental conditions were sampled: clear water reservoir, turbid lagoon two river reaches with waters each. Environmental variables measured situ laboratory. Fishes sampled using trammel beach seine nets. Results Two main scenarios identified: upstream reaches, colder, clearer nutrient-oxygen poor (reservoir its downstream river) where turbidity, dissolved oxygen, temperature, conductivity nutrients largely increased (lagoon river). Fourteen high non-native/native (4:10) ratio collected. Non-native (NNS) confined to lentic conditions, silverside Odontesthes bonariensis dominated. Native (NS) better thrive lotic scenario further favored tolerant species. also seemed influence NNS. Fish assemblage structure considering either, all species, NNS or NS significantly differed among (lentic-lotic) conditions. Total abundance was higher reaches. Species richness diversity by scenario. Beta mostly explained replacement component revealing substitution as pattern variation. Water conductivity, nitrates oxygen most important predictor best frequent explanatory models structures. Conclusions Our results revealed that low diversified Neotropical fauna is disrupted fragmentation due creation artificial impoundments introduction modulate affecting turbid, nutrient-rich pH.