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Impact of origin and condition of host fish (Salmo trutta) on parasitic larvae of Margaritifera margaritifera


Correspondence to: M. E. Österling, Department of Biology, Karlstad University, SE 651 88 Karlstad, Sweden. E-mail:


  1. The highly threatened unionid mussels are obligate parasites on fish. This study investigated larval encapsulation of the freshwater pearl mussel (Margaritifera margaritifera) on its sympatric and three allopatric brown trout (Salmo trutta) strains.
  2. Encystment abundance differed between the brown trout strains shortly after encapsulation. Encystment abundance then decreased at different rates and resulted in a changed relationship in encystment abundance between the brown trout strains when the experiment was terminated. One of the allopatric brown trout strains had higher encystment abundance than the other brown trout strains.
  3. The larvae grew at different rates, and the allopatric brown trout strain with the highest encystment abundance had the largest larvae at the end of the experiment. There was a significant positive relationship between the mean condition factor and shell length of the brown trout strains.
  4. The experiment showed that the potential numbers of juvenile mussels may be restricted at the parasitic life-stage on sympatric brown trout strains. Innate differences in energy resources and immune defence between brown trout strains may be important for parasitic growth, because the condition factor of brown trout strains may be positively related to energy resources for the larvae, and negatively related to host fish immune defence.
  5. The present experiment showed that it may be important to investigate and manage unionid mussels' parasitic larval stage on host fish. Infestation experiments, like the one presented here, may inform managers if the parasitic stage is functioning properly. They can also evaluate host fish strains used for introductions in streams where natural fish strains have disappeared, but mussels persist. Such experiments have applications in breeding programmes for mussels, as this is an increasing management measure in threatened mussel populations.

Copyright © 2013 John Wiley & Sons, Ltd.