Boil the court-bouillon for 30 minutes, put in a tablespoon of olive oil (this helps to keep the skin of the fish from breaking and the outer flesh from flaking). Put in the fish. Poach very gently for 35 minutes. Try with a skewer to see if the flesh easily leaves the bone. Lift out with a perforated slice and serve at once, if it is to be eaten hot, garnished with thin slices of cucumber and accompanied by a hollandaise sauce. If it is to be eaten cold, it should be allowed to cool to blood heat in the bouillon and then lifted and left to become quite cold in the refrigerator. Serve chilled but not icy cold, with mayonnaise and a cucumber and lettuce salad.