Introduction of exotic fish species and decline of native species in the lower Po basin, north-eastern Italy

Freshwater ecosystems worldwide are experiencing native fish losses with severe threats to the conservation of freshwater biodiversity and ecosystem functioning, and the debate on whether the cause is biotic or abiotic disturbance is still open.Temporal variation in fish assemblages was analysed over an 18year period in 14 waterways of the lowland backwaters of the Po River in north-eastern Italy, which are important feeding, spawning and nursery sites for native fish.In 1991, 14 native and eight exotic species were collected. In less than 20years 10 native species underwent local extinction, three of which - Rutilus pigus, Rutilus aula, and Chondrostoma soetta - were endemic to the Padano-Veneto District in northern Italy.Ordination of the data (MDS, CLUSTER, ANOSIM, SIMPER) showed a clear temporal gradient in fish community structure. After the establishment of the exotic predator Silurus glanis, some native species significantly declined in abundance and biomass (i.e. Alburnus arbor...