Nine different species of oysters belonging to the genera Crassostrea, Saccostrea, and Ostrea occur naturally along Pakistan's coastline in the northern Arabian Sea. At the present time, no commercial harvesting or hatchery culture of oysters exists in Pakistan. The world's oyster aquaculture industry is seriously affected by diseases caused by parasites, such as Bonamia ostrea in the European flat oyster Ostrea edulis, and Haplosporidium nelsoni or Perkinsus marinus in the Eastern oyster Crassostrea virginica. Pathogens may be endemic or recently introduced and may cause epizootic mortalities and catastrophic economic losses. To evaluate if there are parasites or diseases in Pakistan's oysters that could limit prospective aquaculture development, histopathological analyses were performed on two oyster species, Ostrea nomades and Crassostrea belcheri. Oysters were sampled year-around, and fixed and processed for histology. Slides (217 cases for O. nomades and 76 cases for C. belcheri) were examined for the presence of parasites or pathological changes. Ostrea nomades was infected by a protozoan parasite, Nematopsis sp. Sneider, 1892 (Apicomplexa, Porosporidae), at 67% prevalence, and C. belcheri at 1.3% prevalence. Nematopsis spp. did not induce pathological changes in the oysters. Stegotricha-like ciliates (Thigmotrichida, Ancistrocomidae) were present in the stomachs of O. nomades with a prevalence of 1%, and 25% of C. belcheri presented ceroid deposits in their tissues. Historically, Ostrea and Crassostrea genera have been associated with epizootic diseases, but in the present samples, no known, economically important parasites or diseases were found. Absence of any pathology in these samples projects a positive future for oyster aquaculture in Pakistan. These oyster populations should be protected from nonendemic bivalve importations, which could transmit new parasites to these potentially susceptible, previously unexposed, native oysters.
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Vol. 27 • No. 4