let 1 leek or green onions get soft in margarine or butter

sprinkle flour over the onion ( 2persons 2-3 tablespoons)

add skin and juice of 1 lemon

add the water from the crayfish tails (about 350 gr)

add Creme Fraiche or cream

let it cook gently for a few minutes

add cubes of salmon and cook about 5 minutes (about 150-200 gr)

just let the crab fish-tails get warm

You can also put in some crab sticks (think I did that when you were here)
Or use shrimps instead of crab fish-tails

put in the last minute in some dill