Clean the fish, remove heads and fins, and cut in pieces.
Arrange the pieces in a fireproof pot, in alternative layers with rings of onion, and some thyme, bay leaves, sprigs of parsley and cloves.
Cover with mild or wine vinegar and water in equal quantities.
Cover the pot with a close-fitting lid, and cook in a moderate oven for 1 hour.
Allow to cool, pour a little oil on the surface of the liquor, cover again and eat after about 5 or 6 days.