Thaw frozen fish. Clean, wash, and dry fish. Cut fish almost through lengthwise and spread open. Sprinkle with salt and pepper.
Melt butter in a 10-inch fry pan. Add dill weed. Place fish in a single layer, flesh side down, in the hot dill butter. Fry at moderate heat for 2 to 3 minutes. Turn carefully. Fry 2 to 3 minutes longer or until fish flake easily when tested with a fork.
Place fish on a warm serving platter. Keep warm. When all the fish have been fried, turn heat very low and stir in lemon juice. Pour sauce over fish.