Occurrence of the haemocyte parasite Bonamia sp. in flat oysters Ostrea puelchana farmed in San Antonio Bay (Argentina).

Culture of native flat oysters Ostrea puelchana d'Orbigny in San Antonio Bay (San Matías Gulf, Argentina) began in 1995. After elevated mortality (33%) occurred in September 1996, 18 mo after immersion, histopathological analysis and evaluation of parasitic prevalence was carried out. In October 1997, after 31 mo of cultivation, cumulative mortality was 80%, and in December of the same year, when individuals reached marketable size, mortality was 95% and culture was discontinued. The present study describes the haemocytic parasitism that affected O. puelchana, and suggests that a Bonamia sp. was the etiological agent. This parasite should be considered as a different species from Bonamia sp. detected in Australia and New Zealand until more studies are made to determine the correct taxonomy. This work constitutes the first record of this haemocyte parasite in flat oysters from the Argentinean coast.