Pearl mussel conservation project reaches next stage
2 March 2011 Last updated at 10:29 GMT
Thousands of baby fish are being released into Northumberland rivers as part of a project to increase the numbers of an endangered mollusc.
Pollution has had a massive impact on the ability of pearl mussels to reproduce, as the species can only survive in very clean water.
But the pearl mussel also depends on healthy fish stocks, as its fertilised eggs must latch on to fish to develop.
Scientists working at the Kielder Hatchery have successfully implanted mussel larvae into the gills of salmon and trout for the first time, and Jeremy Cooke joined them on the River Rede to see their release.