Sauté celery, onion, and garlic in butter in a large Dutch oven until tender. Add tomatoes, tomato sauce, and seasonings, mixing well. Bring to a boil. Reduce heat; cover and simmer 20 minutes.
Add spaghetti and boiling water; mix well. Cover and simmer 10 minutes or until spaghetti is almost tender. Add fish; cover and simmer 10 minutes or until fish flakes easily when tested with a fork.
Spoon stew into individual serving bowls; sprinkle with cheese. Serve immediately.