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Diseases of Aquatic Organisms

    DAO prepress abstract   -  DOI: https://doi.org/10.3354/dao03785

    Infections with Marteilia pararefringens in wild mussels, Mytilus spp., along the Norwegian coast are more frequent than revealed by the national surveillance programme and highlight the need for its improvement

    Mats B√łgwald*, Stein Mortensen

    *Corresponding author:

    ABSTRACT: Norway had historically been considered free of marteiliosis in bivalves since the disease surveillance programme began in 1995. However, in 2016, Marteilia pararefringens, a protistan parasite of mussels Mytilus spp., was described in a heliothermic lagoon – a poll – previously used to produce flat oyster spat. To study whether the parasite was introduced, and possibly spread, via the historical flat oyster networks on the south and west coast, we sampled aquaculture polls that were part of different networks of farmers and wild, natural polls with no aquaculture activity. Additionally, we sampled mussel banks influenced by polls, and sheltered bays that could have a similar environment to that of polls. We identified seven sites with M. pararefringens-infected mussel populations: five were polls used in flat oyster production and two were in fjord areas with no known connection to any bivalve aquaculture. Prevalence ranged between 2% and 88%. At one site, Trysfjorden, we found M. pararefringens in atypical organs, including the gills, mantle, and intestine. Marteilia-like cells were also observed in the epithelium, lumen, and surrounding connective tissue of metanephridia, and in the sinus of the anterior retractor muscle. Our results demonstrate that the parasite is more widespread than previously thought and is neither isolated to polls nor connected directly to aquaculture activity. Lastly, our findings highlight the need for an improved sampling strategy in surveillance programmes to detect marteiliosis in mussels.