Wash, peel and coarsely dice the potatoes. Put the potatoes to one side covered with cold water. Wash the fish and let it drip off on kitchen paper. Wash lemon, dab dry and cut off 4 slices.
Squeeze the rest of the lemon. Wash bay leaves and herbs and shake dry. Divide the laurel into 4 pieces, remove rosemary needles roughly from the stem. Chop parsley roughly. Sprinkle some sea salt and pepper into the abdominal cavity of the fish and add a slice of lemon, a piece of laurel and some parsley.
Place the fish on an oiled tray or in an ovenproof dish and cut the skin several times. Sprinkle with lemon juice. Drain the potatoes, mix with the rosemary and spread around the fish.
Season fish and potatoes with sea salt and pepper and sprinkle everything with oil. Roast in the preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: level 4) for 25-30 minutes.