Preheat the kitchen oven to 180 °C top/bottom heat (160 °C hot air, gas mark 3).
Debone the pike-perch fillet and cut into 200 g pieces.
Clean, rinse and dab carrot, celery and leek and cut into very fine strips. Rinse dill, dab dry and chop finely.
Season pike-perch fillets with salt, pepper and juice of one lemon and place each on two 30 cm long pieces of aluminum foil, place vegetable strips on top, grate a little fresh horseradish on top and season again with salt, pepper and juice of one lemon. Put some butter on top and close the foil well. In the hot stove cook the parcels for
for 12 minutes.
Bring to the table in the foil and open only at the table. It goes well with herb potatoes.