In a large skillet, saute onion and celery in 1/4 cup butter until tender. Remove from the heat; stir in the crab, bread crumbs, mayonnaise, egg, pimientos and seafood seasoning. Spread 1/3 cup crab mixture over fillets. Roll up each from the pointed end; secure with toothpicks.
Place seam side down in a greased 9-in. square baking pan. Melt remaining butter; drizzle over fish. Sprinkle with salt and paprika.
Bake, uncovered, at 400° until fish just begins to flake easily with a fork, 25-30 minutes. Discard toothpicks. Spoon pan juices over fish.