Place a 10- by 15-inch nonstick pan in a 500° oven until pan is hot, about 5 minutes.
Meanwhile, on a plate mix cornmeal, paprika, pepper, and 1/4 teaspoon salt.
In a shallow bowl, beat egg white and milk to blend.
Rinse fish fillets, pat dry, and cut into serving-size pieces.
Coat fish with egg white mixture, then cornmeal mixture. Set aside in a single layer.
When pan is hot, mist lightly with cooking oil spray. Quickly arrange fish pieces well apart in pan. Bake until fish is browned on bottom, 3 to 4 minutes. Turn over and continue baking until fish is golden on top and opaque but still moist-looking in thickest part (cut to test), 2 to 3 minutes longer.
Meanwhile, mix mayonnaise, pickle relish, onion, and vinegar to make tartar sauce.
With a wide spatula, transfer fish to plates; add salt to taste. Serve with tartar sauce and hot sauce.