Freshwater crayfish, a sort of miniature lobster, are native to our lakes and rivers; the indigenous species found in Britain is the Small White-Clawed (Astacus pallipes) but they are increasingly rare due to pollution and being eaten out of house and home by the imported Red Signal which has all but wiped them out.
These come from the West coast of America and have the advantage of being bigger in size, faster growing and disease resistant. These are now much more common than our native White Clawed crayfish which are protected.
Before eating, signal crayfish have to be cleansed to clear out their gut. Larousse Gastronomique goes into elaborate instructions about how to remove the 'media lamina of the tail flukes'. If you do not, 'it spoils their delicate flavour' Luckily this is not as difficult as it sounds, and placing them in a bucket of clean water, changed daily for a couple of days will do the trick. Boiled in slightly salted water, or thrown on the BBQ they taste great!
A simple recipe, and how to shell your crayfish can be found here.