Wash fillets in cold water and pat dry. Sprinkle with salt and pepper. Dredge fillets in flour. Place oil and 2 tablespoons butter in flat, heavy-bottomed skillet and heat on medium-high until butter melts. Keeping heat at medium-high, cook fish on 1 side about 3 minutes (more or less, depending on size of fillets), until deep brown and crispy. Turn fish and cook on second side, about 3 minutes. Turn fish only once.
Remove fish to serving platter. Turn off heat. Into hot skillet, whisk in remaining 1 tablespoon butter. Add lemon juice. Pour in capers, liquid and all. Whisk. Pour thin sauce over fish fillets. serve at once.