Signal crayfish can be identified by the light signal mark behind the claw. It was originally imported to Europe from the US and is more aggressive and more resistant to crayfish plague than the local river crayfish.
A signal crayfish is smoother, lighter and has larger and squarer claws than a. The claws are light on the underside and have a light patch at the base of the "thumb".
Crayfish go red when boiled because the other pigments are broken down by the heat. Signal crayfish get slightly lighter than European crayfish when cooked.
Experts think the females taste best – especially in August when the ovaries are full of roe. The females have a wider abdomen. The ovaries are under the carapace.
How to cook crayfish
Your crayfish should all be alive when you start.
If cooking Scandinavian style, the crown dill in the cooking liquid should have formed seed pods to get the right flavor. Cut the stalks off.
Louisiana style: Add the ingredients according to how long they need to boil. Spices (”Cajun boil seasoning”) and chunky vegetables first, your smoky sausage last. And after that the crayfish – they should only simmer for about five minutes.
Sort the crayfish by size before boiling them in – as a rough idea – three batches. Start with the largest and finish with the smallest.
Make sure the water is boiling properly. Put the first 10 to 20 crayfish in, put the lid on and wait until it boils again before putting in the next batch. After the last batch – once the water has come back to the boil – the crayfish should cook at a lower temperature for about 5 minutes.
Caryfish Louisiana style are eaten while hot, but if you are going to eat them cold:
Cool down the liquid as quickly as you can once you are done. The crayfish need to sit in their own liquid to gain flavor, ideally for a day or longer. If they have to be eaten more quickly, increase the amount of salt in the cooking liquid.
"Louisiana crayfish boil" with corn, potatoes, onions, garlic, bay leaves, Cajun seasoning, smoky sausage and a bucket full of live signal crayfish.