First Reproduction of Asian Carps Revealed in an Artificial Canal Network of Western Europe

Asian carps, namely bighead (Hypophthalmichthys nobilis) and grass carp (Ctenopharyngodon idella), have been widely introduced throughout Europe. As they were considered unable to reproduce naturally under most environmental conditions, little attention was given to their invasiveness potential. We analyzed their population densities, age- and size-structure in an irrigation canal network of Northern Italy. Using a combination of surveys, hydrological modeling, sclerochronology of otoliths and stable isotope analysis of scales we were able to exclude that YOY individuals originated from illegal stockings and that natural recruitment occurs in June. Even if current populations are mainly composed of older individuals originating from past stockings, natural reproduction could partly contribute to higher densities. As Asian carps have thus the potential to become established and even invasive in these areas in the future, further studies are needed to assess this potential. Future management should also account for potential negative environmental effects, controlling the species where needed.