Place catfish in a saucepan with enough water to cover. Bring to a boil, and cook until fish flakes easily with a fork. Drain off water, and mash up the fish. Stir in the onion, mustard, salad dressing, Old Bay(TM), cracker crumbs and egg. Mix until evenly blended.
Heat oil in a large heavy skillet over medium-high heat. Form the fish mixture into patties, and fry in the hot oil. Drain on paper towels, and serve hot.