Combine all the ingredients for the fish marinade in a side bowl and whisk until more or less blended.
Place each fish fillet into the marinade for about a minute per side. Let the marinade drain off, then season the fish with the Creole seasoning or salt and pepper.
Open the broiler and put the fish on the hot broiler rack, skin side down. Top each piece of fish with the butter in slivers. Place the fish under the broiler, about three inches from the heat, for three to six minutes, depending on the thickness of the fish, until the edges are brown and a little crisp. There is no need to turn, unless the fish is more than an inch and a half thick.