The present case study provides an insight into the tissue level pathological alterations inflicted by Bucephalus sp. infections in the edible oyster, Crassostrea madrasensis. Oysters collected during a routine study (from the oyster beds along the Southeast coast of India during July 2012) was found to harbor larval bucephalid infection. Though the prevalence of infection was low (1.37%), the intensity of infection was high, rated as two on the semi-quantitative scale. Infected oyster did not exhibit any external manifestation, but the developing parasitic stages, after replacing the host gonadal tissues have further spread to the gills and digestive glands. Regions of gonadal tissues were found packed with slender, branching sporocysts containing germ balls and crecariae, destroying the acinar architecture of the gonads. Immune responses like encapsulation against the infective stages were totally absent. The altered acinar architecture and reduced volume of the gonadal acini appeared to be insufficient to support any gametic release, resulting in gonadal dysfunction leading to parasitic castration of the host. An increase in the prevalence of Bucephalus sp. infection in the ecosystem could seriously hamper the reproductive potential of the wild stocks of oysters, thereby affecting the viability of oyster farming in the region.

Indian backwater oyster, parasite, trematode, histopathology, sporocyst, parasitic castration.