Histological survey of Pacific oysters Crassostrea gigas (Thunberg) in Galicia (NW Spain)

In Galicia, there is an increasingly interest among representatives of the oyster industry in the development of Pacific oyster Crassostrea gigas culture. Nevertheless severe mortalities and emerging health problems in this species have been recently reported in European farming areas. A histological survey was performed from 2004 to 2009 to assess health status in both cultured and wild Galician oysters. Different symbiotic organisms and conditions were detected, including viral gametocytic hypertrophy (VGH) which is reported here for first time in Spanish coast. VGH, prokaryote-like colonies and ciliates were observed in oyster tissues without causing host damage. A haplosporidian infection, copepods inducing lesions and a cellular proliferative disorder were detected in some samples causing moderate host damage; their low prevalence suggests these parasites are not a threat for C. gigas in Galicia. None of the parasites detected is OIE (Office International des Epizooties: the World Organization for Animal Health) notifiable. Although the current study did not identify any pathogens or diseases of concern, it provides important prevalence baseline data for future health and epidemiological assessments needed to better understanding the existing and emerging health problems in this species.

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► We analyze Crassostrea gigas from Galicia (NW Spain) using histology.
► Viral gametocytic hypertrophy is reported here for first time in Spanish coast.
► Haplosporidians, copepods and neoplasia were detected causing moderate host damage.
► Their low prevalence suggests these parasites are not a threat in Galicia.
► This information provides important baseline data for future health assessments.