Yes, fish and squid can contain parasites, and eating them raw or undercooked can expose you to infection. Cooking seafood to 145°F internally is the clearest way to reduce that risk. Freezing can kill parasites when fish is held at specific time-and-temperature schedules, but it does not kill all harmful germs.
Can fish have worms, and are they dangerous to eat?
Yes. Parasites found in fish and squid include roundworms, tapeworms, and flukes. The main consumer concern is eating seafood raw or undercooked: larvae can then cause infection. The presence of a parasite does not mean that every person who eats the fish will become ill, but no general probability applies across all fish species and sources.
One recognized infection is anisakiasis, caused by roundworm larvae in marine fish or squid. Fish tapeworms are another concern associated with raw or undercooked fish. CDC says anyone who eats undercooked or raw fish or squid is at risk. CDC: About Anisakiasis and CDC: About Diphyllobothrium.
What happens if you eat fish with worms?
Anisakiasis symptoms
Anisakiasis larvae can attach to the wall of the esophagus, stomach, or intestine. Symptoms can include abdominal pain, nausea, vomiting, abdominal distention, diarrhea, blood or mucus in stool, and mild fever. Allergic reactions may include rash and itching; anaphylaxis is uncommon but possible. CDC’s anisakiasis overview.
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When symptoms may begin
Acute abdominal symptoms usually begin within hours of eating infected seafood. If larvae reach the bowel, inflammation can appear one to two weeks later and may resemble other conditions. Symptoms alone cannot confirm the cause, and this information is not a diagnostic checklist. Some infections resolve on their own, but tissue damage can prolong symptoms. CDC: Clinical Overview of Anisakiasis.
When to contact a healthcare provider
Contact a healthcare provider if you develop concerning symptoms after eating raw or undercooked fish or squid, and mention that exposure. Diagnosis may require endoscopy, radiography, or surgery, depending on where a larva is embedded. Do not try to diagnose or treat a suspected parasite infection based on appearance or symptoms alone.
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Does cooking or freezing fish kill worms?
Cooking
The U.S. Food and Drug Administration recommends cooking most seafood to an internal temperature of 145°F. Check the thickest part with a food thermometer; an instant-read thermometer can help verify the temperature. Cooking is the clearest consumer prevention step. FDA: Selecting and Serving Fresh and Frozen Seafood Safely.
Freezing
CDC lists these parasite-control schedules for fish:
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- Freeze at -4°F (-20°C) or below for seven days total.
- Freeze at -31°F (-35°C) or below until solid, then hold at -31°F or below for 15 hours.
- Freeze at -31°F or below until solid, then hold at -4°F or below for 24 hours.
Do not assume an ordinary home freezer reaches or maintains these conditions. Freezing may kill parasites, but FDA cautions that it does not kill all harmful germs; cooking remains the safer choice for minimizing foodborne-illness risk. CDC: About Anisakiasis and FDA seafood safety guidance.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Can you eat fish if you see a worm?
Seeing a worm is not a way to determine whether the rest of a fish is safe. Visual inspection cannot certify seafood as parasite-free, and the cited public-health guidance does not establish that removing a visible worm makes fish safe to eat raw. If you see a worm, do not eat the fish raw; the most reliable consumer safeguard is thorough cooking to 145°F internally. When in doubt about a fish’s handling or condition, discard it rather than relying on appearance.
Who should avoid raw or undercooked seafood?
FDA advises pregnant women, children, older adults, and people with weakened immune systems to avoid raw or undercooked fish and shellfish because they face higher risk from foodborne illness. For these groups, choose seafood cooked thoroughly rather than relying on freezing or visual inspection. FDA: Selecting and Serving Fresh and Frozen Seafood Safely.
Quick Recap
How to choose between raw and cooked fish
- If you want the lowest practical parasite risk: cook the seafood to 145°F internally and verify with a food thermometer.
- If seafood will be served raw: parasite-control freezing must follow a reliable, specified schedule; ordinary home freezing should not be presumed sufficient.
- If you are in an FDA-identified higher-risk group: avoid raw or undercooked fish and shellfish.
- If you are relying on freezing alone: remember that freezing does not eliminate all harmful germs.
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