What can the Limfjord tell us about limiting factors for Bonamia ostreae in northern Europe?
Madsen, L.B.; Kamp, J.; Mellergaard, S. (2013). What can the Limfjord tell us about limiting factors for Bonamia ostreae in northern Europe? Bull. Eur. Assoc. Fish Pathol. 33(5): 165-169
In: Bulletin of the European Association of Fish Pathologists. EAFP: Copenhagen. ISSN 0108-0288, more
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| Authors | | Top |
- Madsen, L.B.
- Kamp, J.
- Mellergaard, S.
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| Abstract |
The Limfjord in Denmark is recognized as a unique production area for European flat oysters, Ostrea edulis, and is the only remaining area in Denmark where the native oyster stock still exists. Up to 1980, the (at that time) low stock of native oysters was supplemented with relaying of foreign flat oysters for fishing for human consumption. In 1980, macroscopic changes similar to those caused by Bonamia ostrea were observed in relayed French oysters, and the diagnosis was verified by histology. Attempts were made to clean the site by fishing up the whole batch of French oysters. During the 1980's, Denmark experienced winters with extremely low water temperatures classified as "ice winters", where the water temperatures stayed below 0°C for up to 11 weeks. In the 1990's, the native stock of flat oysters increased and a surveillance program for B. ostreae and Marteilia refringens was initiated. Neither of the parasites have until now been found. In the same period (from 1998 to 2012) B. ostreae has persisted in eastern waters of the USA (Maine). Here water temperatures have also been below 0°C in some years, but only during one year the temperatures stayed below 0°C for two weeks, where during other four years, the period with water temperatures below 0°C was between 1 and 7 days. It is suggested that the elimination of B. ostreae in Danish waters is due to the extreme climatic conditions like ice winters, either by direct elimination of the parasite or by elimination of the host, the relayed French oysters, thus preventing the spread of Bonamia parasites to the naïve flat oyster population in the Limfjord. |
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