For the pike perch in horseradish crust, finely tear the horseradish. Salt and pepper the skin side of the pike-perch fillets, brush with mustard and press the coated side into the horseradish.
Heat some margarine in a coated pan and sear the fish fillets on the skin side. Turn the pike-perch, add the rest of the margarine, let it stand and serve.
Serve the horseradish-crusted pike perch with rice, parsley potatoes or fresh salad.