The causative agent of crayfish plague, Aphanomyces astaci Schikora, was long considered to be a specialist pathogen whose host range is limited to freshwater crayfish. Recent studies, however, provided evidence that this parasite does not only grow within the tissues of freshwater-inhabiting crabs but can also be successfully transmitted by them to European crayfish species. The potential to act as alternative A. astaci hosts was also indicated for freshwater shrimps. We experimentally tested resistance of two freshwater atyid shrimps: Atyopsis moluccensis (De Haan, 1849) and Atya gabonensis Giebel, 1875. They were infected with the A. astaci strain associated with the globally widespread North American red swamp crayfish, Procambarus clarkii (Girard, 1852), the typical host of the A. astaci genotype group D. As popular ornamental species, both shrimps may get in contact with infected P. clarkii not only in the wild but also in the aquarium trade. We assessed the potential of shrimps to transmit A. astaci to susceptible crayfish by cohabiting A. gabonensis previously exposed to A. astaci zoospores with the European noble crayfish, Astacus astacus (Linnaeus, 1758). In both experiments, the presence of A. astaci infection was analysed with species-specific quantitative PCR. We detected A. astaci in bodies and exuviae of both shrimp species exposed to A. astaci zoospores, however, the intensity of infection differed between the species and analysed samples; it was higher in A. moluccensis and the exuviae of both species. A. astaci was also detected in one A. astacus individual in the transmission experiment. This finding reveals that freshwater shrimps may be able to transmit A. astaci to crayfish hosts; this is particularly important as even a single successful infection contributes to the spread of the disease. Moreover, our results indicate that the tested shrimp species may be capable of resisting A. astaci infection and reducing its intensity through moulting. Although their potential to act as prominent A. astaci vectors requires further research, it should not be ignored as these freshwater animals may then facilitate A. astaci spread to susceptible crayfish species in aquarium and aquaculture facilities as well as in the wild.
