Prepare the broth: Boil 17 pints of water with all the ingredients of the broth, salt and pepper generously. Cover and cook for 1 1/2 hours. Then add the fennel, fresh mint and basil, leave to infuse. Keep warm. Sieve 3/4 the broth. Bring to a boil and plunge in the shellfish one by one without interrupting the boiling. Allow for 11 minutes of cooking for the sea crabs, 9 minutes for the lobsters and 3 minutes for the scampi and the swimming-crabs. Take the shellfish out of the broth. Arrange all the shellfish in a large deep dish, the lobsters being split lengthways (make sure you remove the pouch in the head), the sea crabs being open and halved, their lungs discarded. Pour in the broth and serve.
