| Summary: | Anadromous salmonids migrating in the marine system to feed are at risk of accumulating trophically transmitted parasites that may have negative effects on the salmonid host. The aim of this study was to explore the metazoan parasite community of returning anadromous Arctic charr (Salvelinus alpinus) directly after entrance to freshwater. This is the first study conducted in Europe looking at the parasite community of anadromous Arctic charr. Anadromous Arctic charr were caught migrating upstream in the river outlet from Balsfjord into Laksvatn. Anadromous Arctic charr (n=35) was analyzed for metazoan parasites in all organs. The parasite community of the returning anadromous Arctic charr consisted of 17 different taxa. There was no significant difference in diversity between the number of freshwater parasite taxa (n=8) and marine parasite taxa (n=9). High abundances of parasites were found, with a mean abundance of 5754 individual parasites, with majority being of marine origin. There was a higher proportion of trophically transmitted marine parasites than actively transmitted marine parasites infecting the Arctic charr. This is most likely due to the excessive feeding pattern that the Arctic charr exhibits during their short stay in the marine system. It was discussed whether parasites could be one important reason for the high mortality rate for the Arctic charr at sea found in other studies. Parasites may be an important cost of an anadromous lifestyle; however, it appears as though the cost of parasites does not exceed the benefit of increased body mass and fecundity.
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