Ultrastructural observations on the annual Infection pattern of Bonamia sp. in flat oysters Tiostrea chilensis

Abstract

Ultrastructural observations were made on Bonamia sp. in the oyster Tiostrea chilensis (syn. T. lutaria ) from summer (January) to winter (August), when Bonamia is abundant in oyster tissues. With growth the parasite became more irregular in shape, with more haplosporosomes and mitochondrial profiles, and development of large arrays of smooth endoplasmic reticulum and multi-vesiculate bodies in diplokaryotic plasmodia. Three phases of annual infection were recognised. An incubation phase (September to November) was followed by a proliferation phase (December to May) during which dense forms proliferated and were shed, and a plasmodial phase (June to August). Excretion of lipoid bodies in April, and a drop in lipoid body numbers in June, coincided with the end of the proliferation phase. Dense forms re-appeared during the following plasmodial phase, and may survive through the incubation stage after necrosis of plasmodia at the end of August. Infection patterns in oyster haplosporidians are discussed.