Parasite introduction with an invasive goby in Belgium: double trouble?

Non-indigenous species may negatively impact native fauna in their competition for food and habitat, but they may also introduce non-indigenous parasite species. The invasion of Ponto-Caspian taxa in Western Europe has increased steadily. In 2010, the tubenose goby (Proterorhinus semilunaris) and round goby (Neogobius melanostomus) were observed in Belgium for the first time. To gain insight in the introduction pathways in Belgium and to identify source populations, a phylogeographical and parasitological study was initiated. The mitochondrial cytochrome b gene was sequenced, its haplotype diversity calculated and a statistical parsimony haplotype network built. Both species had a low haplotype diversity compared to native and other non-native populations. The network revealed potential sources in the northern Black Sea for the round goby and in the Danube at the Serbian-Romanian border for the tubenose goby. Prevalence, abundance and infection intensity of ectoparasites was much higher in tubenose goby, which might be the consequence of a different introduction route. Our data provides evidence that tubenose goby entered Belgium through active dispersal. The round goby, however, was most likely introduced with ballast water. We morphologically and genetically document the co-introduction of the Ponto-Caspian Gyrodactylus proterorhini Ergens, 1967, originally described on tubenose goby in southern Slovakia. Because of their direct life cycle and extraordinary reproductive capacities, gyrodactylid monogenean parasites can readily invade new areas together with the host. Moreover, G. proterorhini has a wide host range and might therefore represent a threat to other gobiid fishes. The Gyrodactylus parasite found on the Belgian round goby population has probably been acquired through secondary infection from local fish, as suggested by molecular phylogenetic analysis. The establishment of non-native taxa and their associated parasite and pathogen fauna represents a conservation issue of great concern meriting careful monitoring.