Put the potatoes, tomatoes, and onions in a food processor and process until mushy, but with miniscule chunks. Do this in batches if you must. In a large cast-iron stew pot or Dutch oven, cook the bacon over medium-high heat until crisp, stirring about 5 minutes. Add the vegetable mixture and water, and heat to a point where the broth begins to bubble. Reduce the heat to low and simmer, using a heat diffuser if necessary, until the potato chunks are very soft, about 3 hours, stirring frequently. Stir in the ketchup, Worcestershire, cayenne, salt, and black pepper. Add the catfish and continue to simmer until the fish is cooked through, about 30 minutes. Correct the seasonings and serve.