Q.: Recently I purchased some fresh cod from a reputable market. When I got it home, there was a worm inside. When I called the store, they told me this was very common and that all I had to do was remove the worm and cook the fish as I normally would. Still, I was grossed out. Are worms really common in cod?
A.: Yes, parasite worms are, unfortunately, quite common in cod and other types of white fish.
According to information from the Sea Grant Extension Program at the University of California, Davis’ Department of Food Science and Technology, these roundworms or nematodes, are a very common parasite in certain fish, specifically cod and herring, which is why they often are referred to as cod worms or herring worms.
Salmon and other fresh water fish like trout can carry tapeworms.
Fish get these worms as part of their underwater food chain. Marine mammals eat infected fish, excrete their larvae, which are eaten by shrimp and other small animals, which are in turn eaten by the fish, where they develop into the worms, like the one you saw in your cod.
For the most part, these worms are removed during the processing of fish. Many seafood processors will examine fish fillets over lights, a process called candling, to inspect for worms, but some inevitably will get through.
If you find worms in fish in the future, you can simply remove them, discard them, and cook the fish as you normally would. Proper cooking to at least 140 degrees will kill any parasites. If you are completely turned off, return the fish to the store. A reputable dealer should refund your money without issue. Most fish mongers are familiar with these worms and are also well aware of the gross-out factor on the part of the consumer. Even if you opt to keep the fish, it’s not a bad idea to alert the store to the problem so it can be aware of it for other customers.
According to the UC Davis program, these worms rarely cause problems in humans because they are most often killed during the cooking process if not removed prior.
Should a nematode be eaten live, it can cause severe gastric upset, but a nematode won’t live inside the human digestive tract longer than a week or 10 days. Tapeworms, on the other hand, can live in the digestive tract for years and would need to be treated with medication. Parasites most often become a concern in humans who are eating raw or lightly preserved fish such as sushi, sashimi, ceviche and gravlax, according to the UC Davis program.
To read more information on this topic, visit: www.seafood.ucdavis.edu/pubs/parasite.htm.
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