Heat oven to 425°F. Cut fish into 4 serving pieces. Cut 4 (18x12-inch) sheets of heavy-duty foil. Divide radish and asparagus evenly among and on center of each sheet. Sprinkle each with 1 tablespoon of the sherry and 1/8 teaspoon of the salt. Top with fish. Bring up 2 sides of foil so edges meet. Seal edges, making tight 1/2-inch fold; fold again, allowing space for heat circulation and expansion. Fold other sides to seal.