LAUSR

Abstract Worldwide biodiversity is suffering a “biogeographical homogenization” due to biological invasions. The translocation of freshwater crayfish around the world for aquaculture and the pet trade is also spreading their symbionts, so that all of the association's members have the potential to form invasive populations. In Europe, the signal crayfish, Pacifastacus leniusculus, is often concomitant with the branchiobdellidan Xironogiton victoriensis and through repeated translocations their ranges are expanding. In this study, we report the first observation of X. victoriensis on a native European crayfish population of Austropotamobius pallipes. This work is an alert to the authorities and decision makers on the risks to native species when aquaculture projects introduce alien crayfish species and their symbionts into an area. Future studies are needed to evaluate the impact of this non-native ectosymbiont on native crayfish populations.