McDonald's Filet-O-Fish Born in 1960s with Halibut, Now Features Cod and Iconic Half Slice of Cheese
• Lou Groen created the original Filet-O-Fish in the 1960s with fried halibut and no cheese to attract customers during Lent
• McDonald's executives requested he switch to cheaper Atlantic cod fish, so he added half a slice of cheese to enhance the flavor
• The half-slice of cheese has remained since the sandwich debuted on the national McDonald's menu in 1965
• McDonald's Canada once said the half-slice is the "perfect balance" and more would "overshadow the delicate flavor of the pollock"
• McDonald's U.S. has said the half-slice helps "save on the flavor of the sandwich" but customers can request a full slice