The Limfjord as a Bonamia and Marteilia Free Area

The official EU approved Bonamiosis and Marteiliosis free status for the Limfjord was obtained in 2005 (Commissions Decision 2005/104/EC). According to Directive 2006/88/EC Denmark has to redeclare the bonamiosis and marteiliosis free status - see the Declaration of bonamiosis and marteiliosis free status.  

The Limfjord

The Limfjord is a coastal area of approximately 1.500 km2 dividing the northern part of Jutland in two from east to west, connecting the North Sea and Kattegat. The Limfjord has narrow openings in both ends making it possible for water from the North Sea to flow to Kattegat through the fjord and vice versa. The water in the Limfjord is a mixture of seawater from Kattegat and the North Sea and freshwater from the river systems that falls into the Limfjord.

The Limfjord is the only Danish habitat for natural stock of European flat oyster (Oestrea edulis). Through the 1990ies, the oyster stock increased due to optimal climatic conditions. In 2002, the stock had reached a size where commercial utilization was allowed and since 2003 the annual landings have been approximately 1000-1500 tons oysters.

In the middle of the 1990ies, commercial interests in utilizing the flat oyster as a resource for aquaculture purposes was considered. However, the first experiments on artificial cultivation of oysters did not begin before autumn 2000.

The surveillance programme for Bonamiosis and Marteiliosis in the Limfjord

From 1996 to 2000 an unofficial disease surveillance programme on wild oyster populations for bonamiosis and marteiliosis was conducted in the western Limfjord. The investigations were initiated in order to examine if there was a basis for a future commercial production. Only oysters of the wild population was sampled and examined during the years 1996-2000 because no aquaculture activities were present in the fjord until 2000. The investigations of the wild oyster stocks revealed neither Bonamia ostreae nor Marteilia refringens.

The official Danish surveillance programme for bonamiosis and marteiliosis was initiated in 2000. This surveillance programme has been conducted on the cultivated as well as on wild stocks. The programme was conducted in order to obtain an official EU approved Bonamiosis and Marteiliosis free status for the Limfjord, which was achieved in 2005. During the first two years, biannual sampling of 150 oysters from three different sites was conducted.  From autumn 2002, the sampling was reduced to two annual samplings of 30 oysters from three sites.

Bonamia ostreae or Marteilia refringens have never been detected in the flat oyster stock of the Limfjord.