Preheat broiler high for 5 minutes. Place butter in 13 x 9-inch pan; heat under broiler until melted; set aside. In small bowl, mix together agave, liquid smoke and salt. Place bread crumbs in separate small bowl. Rub salmon fillets with agave mixture, coating all sides. Roll each in bread crumbs. Place salmon in pan and turn once to coat with melted butter. Broil 2 inches form heat source 10 to 15 minutes, or until fish is cooked, turning once.