Haemocytic Parasitosis in the farmed oyster Tiostrea chilensis

Abstract

The present study was carried out in Chiloe island (Chile) in a period between late autumn and early summer in 1997. From a total of 167 specimens histologically analysed, there were two oysters with a haemocytic hyperplasic response in the mantle, gills and digestive gland. The parasited haemocytes contain in the citoplasm a variable number of spherically shapped para-sites similar to the protozoan Bonamia. The genus Bonamia has been described in Tiostrea chilensis from aquaculture farms in New Zealand, which indicates the susceptibility of the Chilean oyster to this parasite. In the present study, an haemocytic parasito-sis is histopathologically described from T. chilensis specimens cultivated in the area sur-rounding Chiloe, Chile. Materials and Methods The 167 specimens of T. chilensis utilized in this study were collected seasonally from late autum in 1996 (June) until the summer 1997 (January). The oysters were obtained from five aquaculture centres located in the south of Chile (Fig. 1), and driven to the laboratory for their analysis. Tissues samples of mantle, digestive gland and gills from each specimen used for the his-tological study were fixed with 10 % (v/v) neutral-buffered-formalin. They were dehy-drated in a series of increasing alcohol con-centrations, cleared in xylene, and embebed in paraffin. Cuts of 5 µm were obtained, stained with hematoxylin-eosin and observed by ligth microscopy at 1400 X magnification.