L'espansione della lasca Protochondrostoma genei (Bonaparte, 1839) nel bacino del fiume Tevere (Italia): stato delle popolazioni e possibili impatti sulle specie endemiche Sarmarutilus rubilio (Bonaparte, 1837) e Squalius squalus (Bianco, 1983)

The Italian nase Prochondrostoma genei is a warm-water species endemic to the Padany-Venetian area (Northern Italy). Since its introduction in the Tiber river basin (Central Italy), occurred more 21 than 50 years ago, the Italian nase has been quickly acclimatized in most of the hydro graphic network and it is still expanding its range. The aims of the study were: i) to analyze the distribution, age and growth of P. genei populations in the Tiber River basin; ii) to investigate the possible impact on the endemics Italian roach Sarmarutilus rubilio and Etruscan chub Squalius lucumonis. Fish and environmental data were collected in 158 sampling sites located on a total of 84 watercourses during the census periods 2000–2005, 2006-2010 and 2011–2015. In the Tiber River basin the Italian nase seems to have found the best deal, compared to its original range, in which was reported a progressive decrease of the species abundances. In the new environments, where the natural resources, in terms of microhabitat and food availability, did not seem to be fully used by the native species and the communities are not satured, P. genei became a member of the fish community without manifesting a particular invasiveness. Probably due to better environmental quality than the native range, the absence of predators and the poor recreational interest of the species, the population status of P. genei can be defined as good, in terms of abundance and growth.