Rinse and pat fillets dry and season with salt. Spread flour in plate and dredge fillets, shaking off excess. Heat 3 tablespoons of butter in skillet over moderate heat until golden brown. Gently lay fillets in skillet and sauté for about one minute on each side. Transfer fillets to two plates. Add lemon juice and remaining butter to skillet; cook until foaming. Add capers and stir. Pour sauce over fish and sprinkle with parsley before serving.