Wash and clean the fish. Cut an orange and a lemon into round slices. Squeeze an orange and two lemons with a juicer. Peel and cut the potatoes into thin round slices. Oil a fairly large baking tray.
Put the thin round potatoes slices on the baking tray. Cover the cleaned and gutted fish with the lemon and orange slices. Place the fish on the potatoes.
Sprinkle the fish with citrus juice. Add oil, salt, marjoram and a few pepper grains. Bake at 200° for 20 minutes.