Roll catfish cubes in flour mixture to coat and shake off excess.
Heat butter in a large pot over medium-high heat until melted and bubbling.
Stir in catfish; cook about 20 seconds per side.
Stir red onion, sherry wine, oysters with liquid, and Worcestershire sauce into the catfish and butter; heat just to boiling, 5 to 7 minutes.
Pour the cream into a small bowl. Ladle about 1/4 of the hot liquid from the pot into the cream; stir to heat the cream evenly. Pour the cream mixture back into the pot; stir. Continue cooking until heated through, being careful not to bring the mixture to a boil, another 5 to 7 minutes.
Ladle into bowls; top with fresh parsley and black pepper to serve.