14 Fish You Should Think Twice Before Eating

Fish is often celebrated as a cornerstone of a healthy diet, offering essential nutrients like omega-3 fatty acids that support brain health, reduce inflammation, and may lower the risk of diseases such as Alzheimer’s, cardiovascular disease, and certain cancers. However, not all fish are created equal — and some could pose serious health or environmental concerns.

Due to industrial activities like coal-fired electricity generation, smelting, and waste incineration, high levels of mercury have found their way into our waterways. This mercury doesn’t just vanish — it enters the marine food chain and bioaccumulates, meaning smaller fish consume it and are then eaten by larger fish, causing mercury concentrations to rise with each step up the food chain. Consuming too much mercury can cause mercury poisoning, which is why the U.S. Food and Drug Administration (FDA) and Environmental Protection Agency (EPA) have issued guidelines on safe consumption levels. The Environmental Defense Fund (EDF) also offers advice on which fish are best avoided.

1. Tilapia

According to a 2008 study from the Journal of the American Dietetic Association, tilapia is surprisingly high in inflammatory omega-6 fatty acids and low in beneficial omega-3s — in some cases, worse than eating bacon. Chronic inflammation is linked to heart disease, cancer, and diabetes. If you must eat tilapia, choose sources from the U.S., Canada, the Netherlands, Ecuador, or Peru, and avoid those farmed in China. Wild-caught tilapia is best, though rare.

2. Atlantic Cod

Once a fishing industry staple, Atlantic cod populations collapsed in the 1990s due to overfishing. Despite reduced catches, recovery has been slow, and the species remains classified as vulnerable. Choosing alternative white fish helps relieve pressure on these struggling populations.

3. Atlantic Flatfish (Halibut, Flounder, Sole)

Overfishing and excessive bycatch plague these species. U.S. fisheries discard about 2 billion pounds of bycatch annually — enough for half a billion meals. The California gillnet fishery, targeting halibut, is among the worst offenders.

4. Caviar

Beluga sturgeon, the source of luxury caviar, can live for a century but is now critically endangered due to overharvesting. Many sturgeon species face similar threats, making their eggs a high-price purchase with a high ecological cost.

5. Chilean Bass

This popular fish contains high levels of mercury, making it a health risk if consumed frequently.

6. Eel

Slow to mature and overfished, eels are essential to aquatic ecosystems. They also absorb pollutants easily, prompting health advisories in certain regions to limit consumption to once a year.

7. Imported Basa, Swai, Tra, Striped Catfish

Often mislabeled simply as “catfish,” these species can carry Vibrio bacteria — a major cause of shellfish poisoning — according to a 2016 study.

8. Imported Farmed Shrimp

Global shrimp farming often uses pesticides banned in the U.S. and heavy antibiotic treatments, increasing the risk of antibiotic-resistant bacteria exposure when handling raw shrimp.

9. Imported King Crab

About 75% of U.S.-sold crab is imported from Russia, where unsustainable fishing is common. Mislabeling is rampant — “Alaskan” king crab might not be from Alaska at all.

10. Orange Roughy

These long-lived fish mature slowly, making recovery from overfishing nearly impossible. They also have high mercury content.

11. Shark

Sharks contain high mercury levels and face population decline from overfishing. Their slow reproduction makes them especially vulnerable.

12. Atlantic Bluefin Tuna

Highly prized yet highly endangered, bluefin tuna are large predators with high mercury content.

13. Swordfish

Another mercury-heavy predator, swordfish is discouraged entirely for women and children, and men are advised to limit intake to once a month.

14. King Mackerel & Grouper

Both contain notable mercury levels. Grouper is also a frequent victim of seafood fraud, with cheaper fish mislabeled as grouper in up to 87% of tested cases.

Selenium’s Role in Mercury Risk

Many fish high in selenium can help counter mercury absorption, but this is not a free pass to consume high-mercury species regularly. Sharks, for example, have high mercury but low selenium — a poor combination for health.

Better Choices

You don’t have to give up fish altogether. Opt for wild-caught Alaskan salmon, Pacific sardines, Atlantic mackerel, U.S./Canada-caught albacore tuna, Alaska cod, Arctic char, or rainbow trout. The EDF Seafood Selector offers comprehensive, sustainable choices with health and environmental benefits.