Right then, lets start at the beginning:     It sounds obvious, but you will need somewhere where there is actually a population of foreign crayfish, not english ones as they are heavily protected. The most common type of invasive crayfish currently found in the UK is the American signal crayfish but there are actually 6 different species currently found. They are:   Signal crayfish Turkish crayfish Noble crayfish Marbled crayfish (also known as Louisiana red swamp) Australian (Spin