Cook bacon in a skillet until crisp; drain bacon, reserving drippings in skillet. Crumble bacon, and set aside.
Sauté onion in bacon drippings until tender; remove with a slotted spoon, and set aside.
Sauté fish in remaining drippings until fish is lightly browned. Remove fish from skillet, and cut into bite-size pieces. Combine bacon, onion, catsup, and 1/2 cup water in skillet. Simmer 5 minutes.
Combine flour, milk powder, salt, and remaining water in a medium saucepan, stirring well. Cook over medium heat, stirring constantly, until thickened. Stir in fish mixture. Cook until thoroughly heated.