Wash fillets and pat dry. Melt butter and set aside. Using a mortar and pestle (if available) or a fork, combine seasonings well and spread on a flat plate. Heat a cast-iron skillet or grill to red hot. Brush fillets with butter and dredge in seasoning. Place fillets in skillet or on grill and cook, depending on thickness, for two to five minutes per side (five minutes per inch of thickness, two and a half for a half-inch-thick fillet) until both sides are crisp and blackened and fish is cooked and tender inside. Serve with melted butter and a slice or two of lemon or lime for each fillet.