McDonald's franchisee Lou Groen realized in 1962 that his cheeseburger sales were down on Fridays, especially during the time leading up to Easter.
The reason? Groen lived in Cincinnati, a heavily Catholic area — and observant Catholics were eschewing hamburgers and other meat products on Fridays as part of their faith.
Ever the business executive, Groen knew there must be something to lure in this customer base on Fridays.
His ingenuity would lead to the creation of the Filet-O-Fish sandwich.
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"With determination and a knack for thoroughness, Groen convinced McDonald’s to test a breaded whitefish sandwich to help satisfy customers who abstained from eating meat on Fridays in observance of Lent," the McDonald's website notes.
That breaded fish sandwich would become known as the Filet-O-Fish.
"My father exemplified Ray Kroc’s philosophy that you can succeed if you put the customer first," Paul Groen told McDonald's.
The younger Groen followed in his father's footsteps and also owns multiple McDonald's locations.
At the time of the creation of the Filet-O-Fish, Lou Groen was "barely doing $300 in daily sales" on Fridays, said Paul Groen.
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"My father needed that fish sandwich to survive and compete against other restaurants. He set in motion a framework of success that would benefit future generations," he said.
At the same time Groen was testing the Filet-O-Fish, McDonald's founder Ray Kroc had another meatless alternative idea: the Hula Burger.
The Hula Burger consisted of a piece of grilled pineapple served on a bun, with cheese.
While Kroc had faith in his creation, the public did not.
The Filet-O-Fish proved to be far more popular than the Hula Burger.
The Hula Burger was discontinued in 1963.
In 1965, the Filet-O-Fish was added to the McDonald's menu nationally — and became the first new product ever added to the chain's original menu.
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At the time, the Filet-O-Fish was priced at $0.29.
It was the only non-hamburger sandwich on the menu, says the McDonald's website.
Its base components – bun, tartar sauce, breaded fish and half-slice of cheese – have remained unchanged since its official launch.
Today, in the United States, the Filet-O-Fish is made of Alaskan pollock.
The sandwich is also available in many countries, with slight regional variations.
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Unlike other fast-food fish offerings, which appear only during Lent, the Filet-O-Fish remains on the McDonald's menu year-round.
And, true to its origins, it remains especially popular during Lent, said the McDonald's website.
A full 25% of all Filet-O-Fish sandwiches are sold during the 40 days of Lent.
Fox News Digital reached out to McDonald's for additional comment.
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