The Filet-O-Fish became McDonald's first nationally introduced fish sandwich.
McDonald's introduced the Filet-O-Fish in 1963 after franchisee Lou Groen developed it for customers in a heavily Catholic neighborhood of Cincinnati, Ohio. During Lent, many customers avoided meat on Fridays, creating a business problem for a hamburger-focused restaurant. Groen proposed a fish sandwich as a way to serve that local demand.
The sandwich was tested against a meatless competitor, the Hula Burger, which Ray Kroc had suggested. The Filet-O-Fish performed better and was added to McDonald's national menu. It therefore represents both a menu milestone and an example of local franchise experimentation influencing the wider brand.
The Filet-O-Fish is sometimes described as the first McDonald's sandwich, but that is incorrect. Hamburgers and other sandwiches were sold earlier. Its distinction is being the first fish sandwich introduced nationally by McDonald's.