Clean and fillet the fish. Sprinkle salt, pepper and spices on the inside of the fish, roll them up and put them into an ovenware dish. Slice the onion finely and scatter the onion rings on the fish, together with the bay leaves. Pour over the ale and the vinegar. Cover and bake at 350°F, 180°C, gas mark 4 for one hour. Serve hot or cold.