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First report on bucephalus infection of the farmed flat oysters ostrea edulis in South-eastern Adriatic, Croatia

Bucephalus infection in different shellfish species has been studied worldwide. These trematodes are widely distributed in temperate and tropical marine waters. Their sporocysts and cercariae infiltrate most body organs of shellfish and have been reported to cause castration, hermaphroditism and protandry and to significantly reduce resistance to environmental stress. To our knowledge, so far, there are no reports on Bucephalus infection in European flat oyster (Ostrea edulis L.) from Croatia. In our study we investigated the incidence of Bucephalus sp. in farmed European flat oyster obtained from the south-eastern Adriatic Sea. Oyster samples were collected monthly in the year 2005. For the purpose of histological examination, soft parts of 30 oysters were fixed in Davidson’ s fixative. The fixed material was embedded in paraffin and serially sectioned at 5 μ m. Sections were stained with hematoxylin and eosin (H&E) and studied by light microscopy using an Olympus BX41 at magnifications of up to 2000x. The infection was evaluated in histological sections and its prevalence was calculated. From the total number of examined oysters the parasite was found in 5, 53%. Percentage of infected speciments in the monthly samples ranged from 0-20%, with the maximum in November. In the winter months, December through March, the infection was not detected (Figure 1). Histological examination revealed changes representative of Bucephalus infection. Sporocysts containing developing cercariae were found in connective tissue around the digestive tubules. Digestive tubules were partially or completely destroyed and the host response included haemocyte infiltration around the sporocysts. The analysis of histopathological changes led to the conclusion that Bucephalus sp. could be a serious cause of mortality in heavily infected European flat oyster, especially in the period after the spawning season.

Bucephalus sp.; shellfish; patohistology

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