Heat large cast iron skillet over high heat for 10 minutes.
Rinse fillets and pat dry. Mix dry seasonings in a freezer bag. Brush both sides of fillets with lemon juice and butter. Sprinkle each side with spice mixture. Place 2 fillets, rounded side down, in hot skillet. Cook over high heat for 2 minutes. Turn fillets and cook 2-3 minutes, or until fish flakes easily when tested ith a fork. Repeat procedure with remaining fillets.