Suitability of different salmonid strains as hosts for the endangered freshwater pearl mussel (Margaritifera margaritifera L.)

The complex life cycle of endangered European freshwater pearl mussel Margaritifera margaritifera L. involves an obligatory parasitic phase on a host fish. Knowledge on the host-parasite interaction and on the suitability of different host fish species and strains is required both for the management of wild fish and mussel populations as well as for improving the efficiency of captive breeding methods.In this study, the suitability of different salmonid strains for hosting glochidia was tested, including Danube salmon (Hucho hucho L.) and three brown trout (Salmo trutta L.) strains from inside and outside the freshwater pearl mussel distribution range. All brown trout strains as well as Danube salmon were successfully infected with freshwater pearl mussel glochidia and encystment of mussel larvae was detected. One brown trout strain originating from the natural pearl mussel distribution range was identified as the most suitable host, revealing the highest fish-weight-normalized infection rates and highest glochidial growth rates, whereas endemic Danube salmon was least suitable. Under natural conditions, the role of Danube salmon may be attributed to the long-distance dispersal of glochidia in the Danube system, whereas sedentary brown trout appear to be the most important hosts at a local scale. Successful infection of suitable hosts and the maintenance of these host-parasite systems in calcareous water were demonstrated in this study. These results indicate that neither the infection process nor the encystment phase of freshwater pearl mussels is dependent on low lime concentrations. The results of this study suggest that careful selection and management of appropriate host fish strains is mandatory for sustainable conservation management of freshwater pearl mussel populations.