Heat a large skillet on medium hi heat for 3 minutes. Melt 2 tbsp butter in skillet. Season flesh side of fish with 1 1/2 tsp Old Bay seasoning. Place fish skin side up in skillet. Cook 5 minutes, turning fish after 3 minutes. Remove fish from skillet; keep warm. Reduce heat to medium.
Stir wine into skillet, scraping bottom to loosen browned bits. Add remaining butter and green onion; cook and stil 1 minute. Gradually stir in cream.
Stir in mustard and remaining Old Bay. Simmer 2 minutes or until slightly thickened. Stir in crabmeat. Return fish to skillet, cover. Cook 3 minutes longer or until fish flakes easily with a fork.