Preheat oven to 350 degrees F.
Rinse, pat dry, and finely chop 1/4 pound mushrooms. Quarter remaining mushrooms or drain canned mushrooms. Set aside.
In a small skillet, melt 2 tablespoons butter; add celery and 3 tablespoons of the onion. Saute for 5 minutes. Combine sauteed celery mixture with mushrooms, water chestnuts, bread crumbs, egg, soy sauce, parsley, and salt and pepper. Mix well and spoon into fish cavities. Secure openings with skewers or toothpicks. Sprinkle both sides of each fish with salt and pepper. Place in a large backing dish. Dot with remaining 2 tablespoons of butter, 2 tablespoons onion, the wine, and water.
Bake uncovered for 45 to 50 minutes. Baste occasionally. Test with a fork. When fish flakes, it's done.