Heat oven to 400°F. Grease shallow roasting pan. Melt 1/4 cup margarine in medium skillet over medium heat. Add celery and onion; cook and stir until tender. Stir in all remaining stuffing ingredients.
Sprinkle inside of fish with 1/2 teaspoon salt. Fill opening with stuffing. Secure edges of fish together with skewers or toothpicks. Place in greased pan; brush with melted margarine.
Bake at 400°F. for 45 minutes or until fish flakes easily with fork, basting occasionally with margarine. Remove skewers before serving. To serve, cut into sections by slicing through backbone.