14 Kinds of Fish You Should Think Twice About Eating
Fish is often considered one of the healthiest foods you can put on your plate. It provides high-quality protein, omega-3 fatty acids, vitamins, and important minerals. Many types of fish can be part of a balanced diet and may support heart and brain health.
However, not every fish is an equally good choice.
Some species can contain higher levels of mercury and other contaminants. Others may come from environmentally damaging fisheries, while certain fish can become risky when eaten raw, improperly stored, or undercooked. For some species, the concern is not that they are always dangerous, but that eating them frequently—or obtaining them from an unreliable source—can increase potential health risks.
The phrase “fish you should never eat” is therefore a little misleading. A better approach is to understand which fish deserve extra caution and why.
Below are 14 types of fish that consumers should think twice about, particularly when they are caught from polluted waters, eaten frequently, or prepared incorrectly.
1. King Mackerel
King mackerel is a large predatory fish found in warm ocean waters. It is popular with recreational anglers and is also sold commercially.
The major concern with king mackerel is mercury. Large predatory fish tend to accumulate mercury because they eat many smaller fish throughout their lives. Mercury exposure is particularly concerning for developing nervous systems.
For this reason, king mackerel is generally considered a fish that people should avoid or severely limit, especially children, pregnant people, and those who may become pregnant.
This doesn't mean that every individual fish contains exactly the same amount of mercury. Contamination varies according to location, size, age, and other factors. Nevertheless, there are plenty of lower-mercury alternatives, making king mackerel an easy species to skip.
2. Shark
Shark may not be an everyday food for most people, but it appears in some restaurants and markets around the world.
Like other large predators, sharks can accumulate relatively high levels of mercury over their long lifetimes. Some species are also vulnerable to overfishing, meaning that eating them can raise environmental as well as health concerns.
Another problem is that consumers may not always know exactly which shark species they are purchasing.
If you're looking for the nutritional benefits associated with seafood, there are generally better options. Smaller, lower-mercury fish can provide protein and beneficial fats without the same concerns associated with large predatory species.
3. Swordfish
Swordfish is prized for its firm texture and rich flavor, particularly when grilled or seared.
Unfortunately, it is also one of the fish commonly associated with high mercury levels.
Swordfish are large, long-lived predators. As they consume other marine animals, mercury can accumulate in their tissues over time.
Occasional consumption may be treated differently from frequent consumption, but people who are pregnant, breastfeeding, or feeding young children should pay particular attention to official seafood-consumption advice.
If you enjoy the texture of swordfish, consider alternatives such as salmon or other lower-mercury seafood.
4. Orange Roughy
Orange roughy is a deep-sea fish that has been commercially harvested for decades.
One of its biggest problems is its biology. Orange roughy can live for many decades and mature relatively slowly. Because of its long lifespan, the fish can accumulate mercury, and because it reproduces slowly, populations can be vulnerable to fishing pressure.
This makes orange roughy a fish worth approaching cautiously for both health and sustainability reasons.
A fish that takes many years to reach maturity can be difficult for wild populations to replace once heavy fishing reduces their numbers.
5. Tilefish
Tilefish is another species for which mercury is a major consideration.
However, there's an important detail: where the fish comes from matters.
Tilefish caught from certain regions can have considerably different contamination levels from those caught elsewhere. This illustrates an important principle when choosing seafood: the name of the fish alone doesn't always tell you whether it is a safe choice.
Always pay attention to local advisories and the source of the fish, particularly when buying wild-caught seafood.
6. Bigeye Tuna
Not all tuna should be placed in the same category.
Tuna varies substantially by species and size. Bigeye tuna, for example, is a large predatory species that can contain elevated levels of mercury.
Tuna is incredibly popular worldwide, appearing in sandwiches, salads, sushi, steaks, and canned products. Because of that popularity, people can unintentionally consume it very frequently.
The important lesson is variety.
Instead of eating the same high-mercury tuna repeatedly, rotate seafood choices and include lower-mercury fish such as salmon, sardines, anchovies, or trout.
7. Marlin
Marlin is another large predatory fish that can accumulate significant amounts of mercury.
Because these fish occupy a high position in marine food webs and can grow large, contaminants become concentrated in their bodies.
Marlin is also an important recreational and commercial species in many parts of the world. Depending on the fishery, sustainability can be another consideration.
For most people, there's little nutritional reason to choose marlin over the many seafood options that generally have lower mercury levels.
8. King Tuna and Other Large Tuna
Tuna deserves special attention because the word “tuna” describes multiple species with very different characteristics.
Large tuna such as bluefin tuna can accumulate mercury and are also subject to significant conservation concerns in some fisheries.
At the same time, tuna can be a nutritious food. The problem is not necessarily tuna itself, but the particular species, size, source, and frequency of consumption.
This is especially relevant to people who eat sushi or sashimi regularly. Consuming large predatory fish frequently can increase exposure to mercury compared with choosing smaller fish.
9. Imported Pufferfish
Pufferfish is famous for one reason: certain species contain tetrodotoxin, an extremely potent toxin.
Unlike mercury, this isn't something that cooking simply makes safe. The toxin can be concentrated in particular organs and tissues, and improper preparation can have serious or fatal consequences.
In countries where pufferfish is legally prepared by specially trained professionals, strict procedures exist for handling certain species.
For the average consumer, however, illegally caught, incorrectly identified, or improperly prepared pufferfish is an obvious risk.
This is one fish where the safest approach is simple: don't experiment with preparation yourself.
10. Raw or Undercooked Fish
Technically, this isn't a particular species—but it belongs on any serious list of seafood risks.
Raw or undercooked fish can carry parasites, bacteria, or viruses. That's why sushi and sashimi should come from reputable establishments that follow appropriate food-safety practices.
Certain fish can be processed specifically for raw consumption, including through freezing procedures designed to control parasites. However, freezing does not eliminate every possible food-safety hazard, and handling remains extremely important.
People with weakened immune systems, older adults, pregnant people, and young children may need to take additional precautions.
The key point is that “fresh” doesn't automatically mean “safe to eat raw.”
11. Fish From Polluted Waters
A perfectly healthy species can become a poor choice if it comes from contaminated water.
Industrial pollution, agricultural runoff, sewage, mining activity, and other environmental contaminants can affect fish populations. Depending on the location, fish may accumulate substances such as mercury, PCBs, or other pollutants.
This is why local fish-consumption advisories are so important.
If you catch your own fish, don't rely only on appearance, smell, or taste to determine whether it's safe. Contaminants often cannot be detected by looking at the fish.
Before eating locally caught fish, check the relevant local or national advisory for the body of water where it was caught.
12. Escolar
Escolar is sometimes sold as a premium fish because of its rich, buttery texture.
That texture comes partly from the fish's unusually high levels of indigestible wax esters.
Eating too much escolar can cause gastrointestinal problems, including diarrhea and abdominal discomfort. Some countries and jurisdictions have restrictions or labeling requirements concerning its sale.
Another issue is mislabeling. Escolar has sometimes been confused with more expensive species.
If you encounter an unfamiliar fish with an extremely rich, oily texture, it's worth confirming exactly what species you're buying and how it should be prepared.
13. Farmed Fish From Unreliable Sources
It would be a mistake to say that all farmed fish is unhealthy. In fact, responsibly farmed seafood can be an excellent part of a nutritious diet.
The concern is how and where the fish was produced.
Poorly managed aquaculture operations can have problems involving water quality, disease management, antibiotics, feed, environmental pollution, or traceability. Standards also vary significantly between countries and producers.
Rather than automatically avoiding farmed fish, consumers should look for reputable suppliers and recognized sustainability or quality certifications when appropriate.
Farmed salmon, trout, tilapia, and other species can all fit into a healthy diet when sourced responsibly.
14. Fish That Has Been Improperly Stored
Even a low-mercury fish can become dangerous if it isn't handled correctly.
Certain species, particularly tuna and other fish with naturally high levels of histidine, can develop histamine when they aren't properly refrigerated. This can result in scombroid fish poisoning.
Importantly, cooking may not eliminate the problem because the histamine can remain in the fish.
Signs of spoilage or contamination can include unusual odor, discoloration, or texture, but appearance isn't always a reliable safety test.
Seafood should be kept properly chilled from the time it is purchased until it is cooked or eaten.
When in doubt about seafood that has been left at unsafe temperatures, throw it away rather than taking a chance.
So, Should You Stop Eating Fish?
Absolutely not.
The headline “14 fish you should never eat” can make seafood sound much more dangerous than it actually is. For most people, the better message is to choose seafood intelligently and eat a variety of species.
Fish provides valuable nutrients, including high-quality protein, iodine, vitamin B12, selenium, and—in some species—omega-3 fatty acids such as EPA and DHA.
The goal isn't to become afraid of seafood. It's to avoid unnecessary exposure to contaminants and foodborne hazards.
Healthier Fish Choices
If you're concerned about mercury, consider making lower-mercury fish the foundation of your seafood choices.
Some commonly recommended options include:
Salmon
Sardines
Anchovies
Atlantic and Pacific mackerel varieties that are low in mercury
Trout
Herring
Pollock
Cod
Shrimp
Catfish
These choices can provide many of the nutritional benefits people seek from seafood while generally presenting fewer mercury concerns than large predatory fish.
However, recommendations can vary by country, species, and source, so consumers should follow the current seafood guidance issued by their local food-safety authorities.
The Mercury Problem Explained
Why does mercury appear so often in discussions about fish?
The answer is bioaccumulation.
Mercury enters aquatic environments through both natural processes and human activities. Some microorganisms convert mercury into methylmercury, which can then enter the food chain.
Small organisms are eaten by small fish. Larger fish eat those fish. Predators eat the larger fish.
Over time, mercury can become increasingly concentrated higher up the food chain.
This is why a large, long-lived predator such as swordfish can contain substantially more mercury than a small fish such as a sardine.
For most adults, occasional consumption of higher-mercury fish isn't necessarily equivalent to immediate poisoning. The concern is primarily cumulative exposure, which is why seafood guidelines emphasize species and frequency.
Pregnant People and Children Need Extra Attention
Mercury deserves particular attention during pregnancy because the developing nervous system is particularly sensitive to exposure.
That doesn't mean pregnant people should eliminate seafood. Quite the opposite: seafood can provide important nutrients during pregnancy.
The smarter strategy is to choose lower-mercury seafood and follow current pregnancy-specific consumption recommendations.
Children also have smaller bodies and developing nervous systems, so their seafood portions and species choices should be appropriate for their age.
What About Sustainability?
Health isn't the only reason to think carefully about seafood.
Some fish populations have been heavily exploited, while certain fishing methods can damage habitats or result in unwanted bycatch.
A responsible seafood choice considers several questions:
Is this fish low in contaminants?
Was it harvested responsibly?
Do I know where it came from?
How frequently am I eating it?
Was it transported and stored safely?
No single label or category answers every question.
That's why seafood consumers should look beyond attractive packaging and learn to pay attention to species, origin, fishing method, and reliable certification or advisory information.
How to Make Better Choices at the Fish Market
You don't need to memorize dozens of scientific names to buy safer seafood.
Start with a few simple habits.
1. Know your fish
If a market or restaurant simply calls something “white fish” or “tuna,” ask what species it actually is.
2. Check the source
Knowing where seafood was caught or farmed can help you make a more informed decision.
3. Rotate species
Don't eat the same potentially higher-mercury fish every day. Variety reduces the chance of excessive exposure to a single contaminant.
4. Follow local advisories
Especially when eating fish you've caught yourself.
5. Keep seafood cold
Refrigerate seafood promptly and don't leave it sitting at room temperature.
6. Cook fish properly
Proper cooking reduces many foodborne risks, although it does not remove every contaminant.
7. Be particularly careful with raw seafood
Choose reputable restaurants and suppliers that follow appropriate food-safety procedures.
The Bottom Line
The idea that there are “14 kinds of fish you should never eat” makes for an attention-grabbing headline, but the reality is more nuanced.
King mackerel, shark, swordfish, orange roughy, some tilefish, bigeye tuna, marlin, and certain other large predatory fish can contain higher levels of mercury. Pufferfish can present a serious toxin hazard if improperly prepared. Fish from polluted waters can contain environmental contaminants, while improperly stored or undercooked seafood can cause foodborne illness.
But this doesn't mean you need to eliminate fish from your diet.
In fact, seafood can be an excellent source of protein and beneficial nutrients. The smartest approach is to choose lower-mercury species more often, vary the seafood you eat, buy from reliable sources, follow local advisories, and handle fish safely.
So before putting fish on your plate, don't simply ask, “Is fish healthy?”
Ask a better question:
“What kind of fish is this, where did it come from, and how often should I eat it?”
That small change in thinking can help you enjoy the nutritional benefits of seafood while reducing avoidable health and environmental risks.
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