Cut fish into 6 portions.
Place in a single layer, skin side down, in a well-greased baking dish, 12x8x2 inches.
Combine onion, orange and lemon juice, orange rind and salt.
Pour over fish; cover and place in refrigerator to marinate 30 minutes.
Sprinkle fish with nutmeg and pepper.
Bake in a moderate oven, 350, for 25 to 30 minutes or until fish flakes easily when tested with fork.