In a skillet, saute 1/4 tbsp butter and onion, until tender but not brown. Stir in drained mushrooms, crabmeat, clams, shrimp, crackers, parsely, 1/2 tsp salt, dash pepper.
Spread onto fillets. Roll and place seam side down in a butter baking dish. Preheat oven to 400 degrees.
Sauce: in a saucepan melt 3 tbsp butter, whisk in 3 tbsp flour, 1/4 tsp salt and add milk to the reserved mushroom liquid to make 1 1/2 cups and add 1/2 cup wine. Cook until thick and bubbles. Add salt and pepper to taste.
Pour over fillets and bake for 25 minutes. Sprinkle wiht cheese and paprika and bake 10 minutes longer or until fish is flaky.