Cook bacon in a large stock pot until crisp; drain bacon on paper towels, reserving 1/4 cup drippings in stock pot. Crumble bacon, and set aside.
Sauté onion in drippings until tender. Stir in water, potatoes, tomatoes, and reserved bacon; bring to a boil. Reduce heat; cover and simmer 3 hours. Stir in catfish; cover and continue to simmer an additional 30 minutes. Stir in catsup and salt and pepper; cook until thoroughly heated.
Ladle stew into individual serving bowls. Serve hot.