Extensive farming entails
that the larvae are caught from wild oysters. It makes large
demands on the availability of natural larvae.
Already in 200 B.C., larvae were caught in southern Europe
by placing out bunches of twigs, and afterwards the collected larvae were
placed in salt water ponds and given a continual supply of water and food.
This technique is still used today, but the larvae collectors limewashed
In Norway there are natural conditions that enable farming
using a special technique. There are many small, shallow and nearly enclosed
bays, known as "polls", that during the summer became surprisingly
warm. In the beginning of April, cages with the breeding oysters, are
placed at a depth of between 2-3 metres, where the water is warmest. Between
June and July, the larvae are collected on the bunches of twigs that hang
at the same depth. In this way, oysters have been farmed in Norway since
In Sweden, using imported larvae, oyster farming has been
practiced for more than 100 years. Probably the most successful farming
operation was between 1934-39 in the Stigfjord between Orust and Tjörn,
but the second world war and cold winters have stopped the operation.
Intensive farming entails that wild oysters
are reproduced and grown in land based farms. The larvae are grown under
good conditions that promote rapid growth and survival, and offer a suitable
bedding for when the free swimming stage ceases. After a few months they
are placed in the sea until they reach a commercial size, 7 cm in 3 years.
At the Tjärnö Marine Biological Laboratory a project to try
and farm oysters intensively is in progress, but at present, researchers
need to find out more about the mechanisms that steer the survival of
free swimming larvae. It appears that the composition of unsaturated fatty
acids is decisive.
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