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Northern Pearl Mussel Project Reaches Next Stage

Breeding & genetics

UK - Thousands of baby sea trout carrying freshwater pearl mussel larvae in their gills have been released into the Rivere Rede.

The BBC reports that this is the next stage in a seven-year project which has seen scientists at the Kielder Hatchery working to breed pearl mussels. Salmon and sea trout are, of course, a very necessary part of the complex pearl mussel breeding cycle.

The male pearl mussels release sperm into the water, which is then filtered by the females. The eggs are fertilised, and develop in the female’s breeding pouch before being released as larvae. Each female mussel can release up to four million larval mussels. These larvae (also known as glochidia) are then washed downstream by the flow of the river, and if they are lucky they attach themselves to the gills of young salmon or trout.

The young mussels live as a parasite on the gills of the fish for approximately nine months, before dropping off the fish and settling into the river gravels. They then grow in the river bed and develop into juvenile pearl mussels. The juvenile mussels take about 15 years to mature, and during this time they are very sensitive to pollution and sedimentation.

Pearl mussels are a very important “indicator species”, which show the health of our river systems. When species like this start to disappear, then we know that all is not well with the river eco-system.

In many UK rivers, they have been wiped out by pollution, siltation and illegal over-fishing.