Determining culture strategies in populations of the European flat oyster, Ostrea edulis, affected by bonamiosis

Bonamiosis affects the viability of oyster culture in Galicia (NW Spain). This study shows the effects of the disease on three oyster populations from hatcheries in different culture areas (Cambados and Bueu) and different origin: stock A [F₁]_, stock B [F₂]_, and stock C [F₂]. These stocks were cultured between November 1998 and November 2000 in Cambados and Bueu. In the Cambados area, bonamiosis is considered to be endemic, while the disease does not generally affect Bueu area. Sampling was conducted at 3-month intervals to study prevalence of Bonamia, mortality and growth rates. In the Cambados area, bonamiosis was detected 12 months after beginning culture but in the Bueu area, it was not detected until 24 months after initiating cultures. Our results suggest that there is a relationship between presence of Bonamia ostreae and oyster mortalities, which were observed in the three stocks from Cambados. These mortalities were associated with the culture area (Cambados) and not with stock of oysters. Growth was satisfactory in both areas as oysters reached commercial size (60 mm) 15 months after beginning the cultures. In an area where Bonamia is present, such as Cambados, the oysters should be marketed promptly (after approximately 15–18 months of culture) but in areas where Bonamia is not present, such as Bueu, the oyster farmer can culture oysters over a long period of time, prior to harvest, if necessary.