The surveillance and control program for bonamiosis and marteiliosis in European flat oysters, Ostrea edulis in 2023

Abstract

The surveillance program for the molluscan diseases bonamiosis and marteiliosis is carried out by the Institute of Marine Research according to a contract with the Norwegian Food Safety Authority. In 2023, flat oysters were sampled from four locations: A breed poll where oyster spat is produced, an abandoned breed poll where oyster spat was previously produced, and two fjord systems with larger populations of flat oysters. Samples were collected in April – June and September, to be able to detect Bonamia sp. and Marteilia sp. during the periods when the potential prevalence is highest. No abnormal mortalities were observed during the surveillance. Bonamia ostreae / B. exitiosa and Marteilia refringens were not detected. Marteilia refringens Type O and M are now divided into two species; Marteilia refringens in flat oysters and M. pararefringens in blue mussels. Blue mussels are therefore no longer considered susceptible hosts for M. refringens, but our research project shows that the related Marteilia pararefringens is widespread in certain mussel populations along the South and West coasts of Norway. M. pararefringens can have a serious impact on blue mussel populations, and consideration should be given to listing the parasite on a national list. Furthermore, we propose a formal application for disease free status for Bonamia spp. and Marteilia refringens in Norwegian flat oysters

The surveillance and control program for bonamiosis and marteiliosis in European flat oysters, Ostrea edulis in 2023