Nutrition Diet: When should we avoid eating fish?

October 26, 2025 •

4 min read

According to the U.S. Food and Drug Administration (FDA), certain populations, including pregnant women and young children, must limit or completely avoid specific high-mercury fish. Understanding when should we avoid eating fish is key to a safe and healthy diet, mitigating risks from contaminants, allergies, and foodborne illnesses.

Quick Summary

This guide explains the circumstances under which fish consumption should be avoided or limited. It covers high mercury content in certain species, the dangers of raw or undercooked fish, specific allergies, and the risks associated with poor handling and environmental pollutants.

Key Points

High-Mercury Fish: Pregnant women, young children, and women planning pregnancy should avoid large, predatory fish like shark, swordfish, and king mackerel due to high mercury content.
Raw Fish Risks: Vulnerable populations, including the elderly and immunocompromised, should not eat raw or undercooked fish to prevent illness from bacteria and parasites.
Thorough Cooking: Always cook fish to an internal temperature of 145°F (63°C) to kill harmful bacteria and parasites, ensuring it is opaque and flakes easily.
Seafood Allergies: Individuals with fish or shellfish allergies must practice strict avoidance, as even fumes from cooking can trigger a severe allergic reaction.
Scombroid Poisoning: Avoid improperly stored or handled fish, especially tuna and mackerel, as it can contain high levels of histamine that are not destroyed by cooking.
Local and Seasonal Warnings: Pay attention to local and regional advisories for fish caught in potentially polluted waters or during breeding seasons to avoid contamination risks.

When High Mercury Levels Pose a Risk

For many, fish is a staple of a healthy diet, rich in lean protein, omega-3 fatty acids, and other essential nutrients. However, the primary concern leading to the avoidance of certain fish is mercury contamination. Mercury is a naturally occurring element that, when converted to methylmercury in aquatic ecosystems, accumulates in the flesh of fish. This accumulation is most significant in large, predatory fish that are high on the food chain and live longer, as they consume many smaller fish, leading to a build-up of mercury in their tissues.

Populations at heightened risk

The effects of methylmercury are particularly harmful to the developing nervous systems of fetuses, infants, and young children. Therefore, health authorities strongly advise limiting or avoiding high-mercury fish for the following groups:

Pregnant and breastfeeding women
Women planning a pregnancy
Young children

Fish to avoid or limit due to mercury

To minimize exposure, these at-risk groups should avoid species known to have high mercury levels, such as:

Shark
Swordfish
King Mackerel
Marlin
Bigeye Tuna
Tilefish (from the Gulf of Mexico)

For all consumers, moderation is key when it comes to these high-mercury species. The body can clear mercury over time, so occasional consumption is less of a concern than regular intake. However, selecting low-mercury alternatives like salmon, sardines, and trout is a safer choice.

The Dangers of Raw or Undercooked Fish

Eating raw or undercooked fish, including popular dishes like sushi, sashimi, and ceviche, carries a significant risk of foodborne illness caused by bacteria and parasites. Cooking fish to a proper internal temperature of 145°F (63°C) is the most effective way to kill these harmful pathogens.

Pathogens found in raw seafood

Bacteria: Raw or improperly handled fish can harbor bacteria such as Salmonella, Vibrio vulnificus, and Listeria. These can cause symptoms ranging from mild gastrointestinal distress to life-threatening infections, especially in vulnerable individuals.
Parasites: Fish can contain parasitic worms like anisakids, which can cause severe gastrointestinal issues in humans. Freezing can kill some parasites, but thorough cooking is the only reliable method to eliminate this risk.

Certain groups, including pregnant women, the elderly, young children, and those with compromised immune systems, should avoid raw and undercooked fish entirely to prevent serious illness.

Understanding Fish and Shellfish Allergies

Allergies to fish and shellfish are common and can range from a mild reaction to severe, life-threatening anaphylaxis. It is a common misconception that a person allergic to shellfish is also allergic to finned fish. While some people may be allergic to both, the allergies are caused by different proteins.

Key points about seafood allergies

A reaction can occur not only from eating the fish but also from touching it or inhaling the steam from cooking.
Symptoms can include hives, swelling, nausea, abdominal pain, and respiratory issues.
Cross-reactivity between different types of finned fish or shellfish is possible, so a diagnosis from an allergist is crucial to determine safe consumption.
If you have a diagnosed fish or shellfish allergy, strict avoidance of the allergen is the only safe course of action.

Poor Handling and Spoiled Fish

Even with proper cooking, fish that has been poorly handled or improperly refrigerated can pose a risk. One such danger is scombroid poisoning, or histamine fish poisoning. This occurs when certain fish, like tuna and mackerel, are left unrefrigerated, allowing bacteria to produce high levels of histamine. Cooking does not destroy the histamine once it has formed.

Signs of spoiled fish

When buying fish, look for signs of freshness to minimize risk:

Smell: A mild, fresh scent, not a strong, fishy or ammonia-like odor.
Eyes: Clear and shiny, not cloudy or sunken.
Flesh: Firm and springs back when pressed, with no discoloration.
Handling: Always refrigerate fish promptly and use or freeze within 1-2 days.

Comparison of High-Risk vs. Low-Risk Seafood


High-Risk (Avoid/Limit)	Low-Risk (Safer Choices)
Shark, Swordfish, King Mackerel, Bigeye Tuna	Salmon, Sardines, Canned Light Tuna, Trout, Anchovies
Raw/Undercooked Fish & Shellfish (Sushi, Oysters)	Fully Cooked Fish & Shellfish
Fish from polluted local waters	Seafood sourced from certified, clean waters
Fish causing allergic reactions	Allergist-approved alternatives
Fish improperly refrigerated or handled	Freshly caught or properly frozen/stored seafood

Environmental Factors and Special Considerations

Beyond mercury and food safety, other environmental and situational factors should influence your decision to eat fish. For example, some regional traditions and health advisories suggest avoiding certain fish during the monsoon or breeding season. During these times, water contamination from runoff is higher, and fishing bans are often in place to protect ecosystems.

Another factor is the origin of the fish—farmed versus wild-caught. While farmed fish may have a more consistent nutritional profile, wild-caught fish often have a leaner and cleaner flavor. The potential for contaminants in farmed fish, such as antibiotics or pesticides, is a consideration, though most operations are regulated. Consumers should also be aware of local fishing advisories that warn of pollution in specific waterways. Organizations like the Monterey Bay Aquarium's Seafood Watch offer excellent guidance on sustainable and healthy choices.

Conclusion

While fish is an undeniable part of a healthy diet, particularly for its omega-3 content, informed choices are necessary to protect your health. For some, like those who are pregnant or have specific allergies, avoiding certain types of fish is not just recommended, but essential. For others, exercising caution with raw preparations and understanding potential risks from contamination is a key part of responsible eating. By considering factors like mercury levels, cooking methods, potential allergies, and the origin of your seafood, you can make smarter, safer choices for yourself and your family.

For more information on seafood safety and federal guidelines, you can visit the official FoodSafety.gov website.

Frequently Asked Questions

Pregnant women should completely avoid fish with the highest mercury levels, including shark, swordfish, king mackerel, and marlin.

Canned light tuna is generally low in mercury and safe for pregnant women to consume in moderation. The FDA recommends limiting consumption to 2 to 3 servings per week.

Yes, even without an allergy, eating raw fish can cause foodborne illness from bacteria like Listeria and Vibrio, as well as parasitic infections from worms.

Scombroid poisoning is caused by high levels of histamine in certain fish, typically from improper refrigeration. To avoid it, always buy fresh fish from a reputable source, check for a mild scent, and store it properly.

Not necessarily. While some people are allergic to both, allergies to finned fish and shellfish are distinct. Consult an allergist to determine your specific allergies.

To ensure fish is fully cooked, check that it reaches an internal temperature of 145°F (63°C). The flesh should be opaque throughout and flake easily with a fork.

Yes, it's important to consider environmental factors. Farmed fish may contain antibiotics, while wild-caught fish from polluted areas may have contaminants. Checking local advisories is recommended.