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Diseases of Aquatic Organisms

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DAO 148:153-166 (2022)  -  DOI:

Infection cycle of Marteilia pararefringens in blue mussels Mytilus edulis in a heliothermic marine oyster lagoon in Norway

Mats Bøgwald1,*, Cecilie K. Skår1, Egil Karlsbakk1,2, Anders Alfjorden3,4, Stephen W. Feist5, David Bass5,6,7, Stein Mortensen1

1Institute of Marine Research, 5005 Bergen, Norway
2University of Bergen, Department of Biological Sciences, 5007 Bergen, Norway
3Uppsala University, Department of Organismal Biology, 75236 Uppsala, Sweden
4National Veterinary Institute (SVA), Department of Animal Health and Antimicrobial Strategies, 75189 Uppsala, Sweden
5International Centre of Excellence for Aquatic Animal Health, Centre for Environment, Fisheries and Aquaculture Sciences (Cefas), Weymouth DT4 8UB, UK
6Department of Life Sciences, The Natural History Museum, London SW7 5BD, UK
7Sustainable Aquaculture Futures, Biosciences, College of Life and Environmental Sciences, University of Exeter, Stocker Road, Exeter EX4 4QD, UK
*Corresponding author:

ABSTRACT: Agapollen is a traditional heliothermic marine oyster lagoon in western Norway, representing the northernmost site of any Marteilia sp. protists detected in Europe. The semi-closed lagoon is a unique site to study the life cycle and development of M. pararefringens in naïve mussels. Two baskets with uninfected mussels were deployed in the lagoon outlet in May and October 2018, respectively, and sampled every 6 wk. The parasite was first detected in the mussels by PCR in early July and by histology in late August. By then, M. pararefringens had developed into mature stages, indicating a rapid development during mid-summer. Sporulation occurred during autumn. Mussels deployed in October never became infected, indicating that transmission was restricted to the warmest period of the year. Pronounced pathology was observed in infected mussels, including degenerated digestive tubules and infiltration of haemocytes. Mussel mortality was observed in the baskets, but whether this was due to infections of M. pararefringens or other environmental factors could not be determined. Plankton samples from the lagoon were also collected for PCR analysis. These samples, dominated by copepods, were positive for M. pararefringens in summer. In sorted samples, M. pararefringens was detected in the Acartia spp. and Paracartia grani fractions between July and October. These plankton copepods are therefore potentially involved in the life cycle of M. pararefringens.

KEY WORDS: Marteilia pararefringens · M. refringens M-type · Marteilia maurini · Mytilus edulis · Pathogen · Life cycle · Parasite · Development · Histopathology · Norway

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Cite this article as: Bøgwald M, Skår CK, Karlsbakk E, Alfjorden A, Feist SW, Bass D, Mortensen S (2022) Infection cycle of Marteilia pararefringens in blue mussels Mytilus edulis in a heliothermic marine oyster lagoon in Norway. Dis Aquat Org 148:153-166.

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