The Filet-O-Fish was created to appeal to Catholic customers who avoided meat on Fridays.
McDonald’s franchisee Lou Groen developed the sandwich in the early 1960s while operating in a heavily Catholic Cincinnati neighborhood. Friday restrictions on eating meat created a recurring sales challenge, especially during Lent, so Groen proposed a fish-based menu option.
The sandwich was tested against a meatless competitor before McDonald’s adopted it. Its continued presence helped turn a regional religious and cultural sales problem into a lasting menu and branding success.
The Filet-O-Fish is sometimes mistaken for a product created as a general seafood trend. Its origin was more specific: it was designed around customer habits associated with Friday meat abstinence. The sandwich later became a regular McDonald’s product in many markets.