The surveillance and control programme for bonamiosis and marteiliosis in European flat oysters, Ostrea edulis, and blue mussels, Mytilus sp. in Norway in 2021

The surveillance programme is carried out by the Institute of Marine Research according to a contract with the Norwegian Food Safety Authority. In 2021, samples were collected from one oyster farm, one wild, commercially exploited oyster population which is also used as a source of oysters for a restoration project off the coast of The Netherlands, and one mussel farm. Samples were collected in April/May and in October, to be able to detect Bonamia sp. and Marteilia sp. during the periods when the potential prevalence is at the highest. No abnormal mortalities were observed during the surveillance. Bonamia ostreae / B. exitiosa were not detected. The parasite Marteilia sp. was detected for the first time in mussels, (Mytilus edulis) collected at Bømlo, western Norway in 2016, Tysnes in 2019, and Sunnfjord in 2020. In 2021 Marteilia sp. was found in another site at Bømlo and in Solund. The new detections will be further described in an on-going research project. All isolates found so far are M. pararefringens, which is regarded specific for mussels. The work will be continued in 2022, linked to research on the distribution of M. pararefringens in wild mussels. We propose a revision of the surveillance programme, application for disease free status for Bonamia spp. and Marteilia refringens in Norwegian flat oysters