Potential resistance of a number of populations of the oyster Ostrea edulis to the parasite Bonamia ostreae S.C. Culloty * , M.A. Cronin 1 , M.F. Mulcahy Department of Zoology, Ecology and Plant Science, University College Cork, Lee Maltings, Prospect Row, Cork, Ireland Received 17 March 2003; received in revised form 1 April 2004; accepted 4 April 2004 Abstract The study investigated the susceptibility of a number of European populations of Ostrea edulis to the protistan parasite Bonamia ostreae. The study was carried out at oyster-growing regions in three European countries where Bonamia is endemic. The oyster populations screened during the trial were either: naı ¨ve populations, which had never previously been exposed to the parasite; populations of oysters, which had been exposed to the parasite for a number of years and where no management of the population to try to reduce infection had occurred; and an infected population, where selective breeding has taken place to try to reduce susceptibility to the parasite. Results of the study indicated that this latter population ‘Rossmore’ performed significantly better in some trials than the other populations in terms of prevalence and intensity of infection. Another population from Lake Grevelingen performed best in one trial when cumulative mortality rates were compared. D 2004 Elsevier B.V. All rights reserved. Keywords: Ostrea edulis; Bonamia ostreae; Resistance; Field trial; Parasite 1. Introduction The European flat oyster Ostrea edulis L. is the native species of oyster found throughout Europe and in the past was the basis for oyster production in a number of European countries including France, Ireland, UK, The Netherlands, and Spain (Culloty 0044-8486/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2004.04.007 * Corresponding author. Tel.: +353-21-4904198; fax: +353-21-4270562. E-mail address: s.culloty@ucc.ie (S.C. Culloty). 1 Current address: Coastal and Marine Resources Centre, Environmental Research Institute, University College Cork, Naval Base, Haulbowline, Cobh, County Cork, Ireland. www.elsevier.com/locate/aqua-online Aquaculture 237 (2004) 41 – 58