The surveillance and control programme for bonamiosis and marteiliosis in European flat oysters, Ostrea edulis, and blue mussels, Mytilus sp. in Norway in 2020

The surveillance programme is carried out by the Institute of Marine Research according to a contract with the Norwegian Food Safety Authority. Samples were collected from one oyster farm, four wild oyster populations, one cultivated mussel population and two wild mussel beds. Samples were collected in April/May and in October, in order 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. There have been several reports on mortality or “disappearance” of mussels along the Norwegian coast. The reason(s) for the mortalities have not been determined. However, The parasite Marteilia sp. was detected for the first time in mussela, Mytilus edulis, collected at Bømlo, western Norway in 2016 and Tysnes in 2019. In 2020, Marteilia was detected in wild populations in Sunnfjord and in an open water mussel farm nearby. All detections were M. pararefringens . The work will be continued in 2021, linked to research on the distribution of M. pararefringens in wild mussels. We propose a revision of the surveillance programme combined with the establishment of a new model for health control in mollusk farms, application for disease free status for Norwegian flat oysters and a categorization of zones