Finding a Worm in Your McDonald’s Filet-O-Fish Is ‘Normal,’ Experts Say

McDonald’s Filet-O-Fish, a longtime Lent favorite, is drawing attention after a Reddit user posted photos claiming they found a worm inside the sandwich.

The post, shared to the McDonald’s subreddit, quickly sparked debate and disgust among some users. But others responded with a different reaction.

“Well, now we know it’s real fish,” one commenter wrote.

“My exact thought,” another replied. “I’ve worked fish markets. Fish have parasites.”

According to food writer Matthew Spina of Tasting Table, the presence of a parasite in wild-caught fish is not unusual and can actually indicate that the fish was caught in the wild rather than farm-raised.

Why Parasites Can Be Normal

Spina explains that parasites are common in nearly all wild-caught fish and are “both unavoidable and usually nothing to worry about.”

The parasite most likely to appear in a Filet-O-Fish is a nematode, a type of roundworm commonly found in saltwater species such as cod, pollock, halibut and flounder.

McDonald’s fish patties are made from wild Alaskan pollock, a mild, lean white fish often compared to cod. Because the fish is wild-caught, the presence of occasional parasites is considered a natural occurrence in the seafood industry.

The key factor is cooking temperature. Spina notes that as long as fish is cooked to an internal temperature of at least 145 degrees Fahrenheit, parasites are killed and pose no health risk. McDonald’s deep-fries its Filet-O-Fish patties, a process that exceeds that temperature threshold.

In commercial seafood processing, fish are also inspected and often flash-frozen, which further reduces risk. Still, no inspection system can guarantee that every microscopic parasite is removed before cooking.

A Sandwich With Catholic Roots

The Filet-O-Fish has a long history tied to religious dietary practices.

The sandwich was created in 1962 by Lou Groen, who opened the first McDonald’s franchise in Cincinnati. At the time, many of his customers were Catholic and abstained from meat on Fridays, not just during Lent but throughout the year.

Facing declining Friday sales, Groen developed a fish sandwich with a fried pollock filet and tartar sauce. He presented the idea to McDonald’s founder Ray Kroc, who reportedly preferred the idea of a grilled pineapple sandwich as a meatless alternative.

Groen’s fish sandwich ultimately won out. The Filet-O-Fish became a staple menu item and now sells hundreds of millions of sandwiches annually, particularly during the 40-day Lenten season leading up to Easter.

Consumer Reaction and Perspective

While the idea of finding a worm in a fast-food sandwich may be unsettling, food safety experts emphasize that parasites in wild fish are not uncommon and are typically harmless once properly cooked.

The Reddit post highlights a broader tension between expectations of perfectly processed food and the biological realities of wild seafood.

For customers observing Lent or simply craving a Filet-O-Fish, the presence of a parasite may be unpleasant, but it does not automatically signal contamination or unsafe preparation.

As Spina notes, parasites in wild fish are generally “nothing to worry about” when proper cooking standards are followed.

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