Growth, mortality and disease susceptibility of oyster Ostrea edulis families obtained from brood stocks of different geographical origins, through on-growing in the Ría de Arousa (Galicia, NW Spain)

Infection by Bonamia ostreae has caused extensive mortalities of oysters Ostrea edulis through European and United States coasts for at least 25 years. The development of a bonamiosis-resistant strain seems a promising strategy to fight against the disease. As a first step, evaluation of variability in productive traits and disease susceptibility of European populations was performed to identify favourable oyster populations with which to start selective breeding in Galicia (NW Spain). Oysters taken from Greece, Ireland, Ortigueira (Galicia) and Coroso (Galicia) were used as brood stock, and 19 seed families were produced (4–5 families from each origin). The oyster families were used to assess variability through on-growing in an area of the Ría de Arousa heavily affected by bonamiosis. Results showed significant differences in growth, mortality and susceptibility to bonamiosis and other diseases, both between origins and between families under origins. Bonamiosis was associated with mortality in the late stage of oyster on-growing. Indications of natural selection of bonamiosis less-susceptible oysters due to the long exposure of the Ortigueira population to bonamiosis were found. Other symbionts and pathological conditions were detected, of which herpes-like viral infections and disseminated neoplasia could also cause mortality. An index of the overall incidence of pathological conditions (OIPC) was estimated for each family. A significant correlation between the OIPC and the cumulative mortality of the families was noted. On average, oysters from autochthonous origins showed better performance. The results obtained with the best-performing families suggest that the profitability of oyster farming in Galicia would improve, even under bonamiosis pressure, by using appropriate oyster spat.