top 27 animal alien species introduced into Europe for aquaculture and related activities

The information extracted from IMPASSE, DAISIE, FishBase, and FAO-DIAS inventories of alien species were used to draw a list of the 27 most utilized animal alien species for aquaculture and related activities (e.g. stocking, sport fishing, ornamental purposes) in Europe. Three variables have been considered to assess their negative ecological impacts when these species escape from aquaculture facilities: (i) their distribution across Europe (including non-EU Member States); (ii) evidence of their environmental impact in the wild; and (iii) evidence of their being vectors of non-target alien species and other hitchhikers (e.g. pathogens). Drivers of use and mechanisms of dispersal in the wild have been also considered and reviewed. Twenty of the species are freshwater fishes: alien cyprinids and salmonids have been introduced into Europe mainly for food production, sport fishing and ornamental purposes. The most widespread species are the goldfish Carassius auratus and the rainbow trout Oncorhynchus mykiss, established in 29 and 28 European countries, respectively. Notwithstanding their successful distribution in Europe, only the Gibel carp Carassius gibelio and the peneid shrimp Marsupenaeus japonicus were found to have environmental impact in all the countries of establishment. Crayfish and predatory fishes (e.g. catfishes and salmonids) cause major environmental impacts in Europe by outcompeting native species and altering habitat structure. Alien crayfish, Procambarus clarkii and Pacifastacus leniusculus, are responsible for the largest range of impacts (i.e. crayfish plague dissemination, bioaccumulation of pollutants, community dominance, competition and predation on native species, habitat modifications, food web impairment, herbivory and macrophytes removal). Cyprinids (e.g. herbivorous carps) are vectors of diseases and parasites, while salmonids (e.g. Salvelinus fontinalis) often cause genetic impairment of native stocks by hybridization. The importation of alien farmed (target) species frequently leads to the introduction of associated non-target species. The cultures of the Pacific cupped oyster Crassostrea gigas and Manila clam Ruditapes philippinarum were responsible for the introduction of the largest number (60) of non-native invertebrates and algae, often attached to packaging material, fouling the shell or parasitizing bivalve tissues.