6 Types of Fish You Should Think Twice About Buying: Mercury Risks Doctors Want Families to Know

3. King mackerel

Mackerel is often considered a nutritious seafood choice because it provides protein and omega-3 fatty acids.

However, consumers need to distinguish between different types of mackerel.

Atlantic mackerel and Pacific chub mackerel are classified as Best Choices by the FDA.

King mackerel is different.

It is a larger predatory species that can contain much higher mercury concentrations.

The FDA places king mackerel in the Choices to Avoid category.

This distinction is important because simply asking for mackerel at a seafood counter may not provide enough information.

Consumers should identify the exact species before purchasing it, particularly when preparing meals for pregnant women or children.

4. Marlin

Marlin is another large predatory fish found in tropical and subtropical oceans.

It is sometimes served as a steak because of its firm texture.

Like swordfish, marlin feeds on other marine animals and can accumulate mercury over time.

The FDA includes marlin among the fish with the highest mercury levels.

For families who regularly purchase seafood, it is worth checking restaurant menus and market labels rather than assuming that every type of fish steak is equally suitable.

5. Orange roughy

Orange roughy is a deep-sea fish that has historically been sold as an inexpensive white-fleshed seafood option in some markets.

Its mild taste and firm texture make it suitable for several cooking methods.

However, this fish is particularly notable because it can live for an exceptionally long time.

Some orange roughy may live for more than a century.

A long lifespan allows mercury to accumulate in their bodies over many years.

The FDA therefore places orange roughy in the highest-mercury category.

Its relatively mild flavor should not be confused with a low level of contamination.

6. Tilefish from the Gulf of Mexico

Tilefish is another example of why identifying the exact origin of seafood matters.

Not all tilefish have the same mercury classification.

The FDA distinguishes between tilefish from the Atlantic Ocean and tilefish from the Gulf of Mexico.

Atlantic tilefish is listed as a Good Choice.

Tilefish from the Gulf of Mexico is listed as a Choice to Avoid because of its higher mercury levels.

This distinction shows why broad labels can sometimes be misleading.

The name of the species alone may not provide enough information. Its geographic origin can also matter.

What about bigeye tuna?

There is one additional fish that deserves attention.

Bigeye tuna is also classified by the FDA as a Choice to Avoid because of its high mercury levels.

It is frequently used in sushi, sashimi, and other seafood dishes.

This is why the image's headline referring to six types is not a complete list of every fish in the FDA's highest-mercury category.

There are seven entries in the FDA's current list:

1. King mackerel.

2. Marlin.

3. Orange roughy.

4. Shark.

5. Swordfish.

6. Tilefish from the Gulf of Mexico.

7. Bigeye tuna.

These classifications are based on mercury exposure, not on whether the fish is fresh, frozen, inexpensive, or expensive.

Chapter 3: The Hidden Risk of Mercury and Why Cooking Cannot Remove It

One of the most common misunderstandings about seafood safety is the belief that cooking fish thoroughly removes harmful contaminants.

Cooking is essential for reducing the risk of foodborne illness, but it does not eliminate methylmercury.

This is because mercury is not simply sitting on the surface of the fish.

It is present throughout the fish's muscle tissue.

Washing, soaking, frying, steaming, boiling, or grilling cannot reliably remove it.

The FDA specifically explains that cleaning and cooking fish do not reduce its mercury content.

Why mercury is different from ordinary food contamination

Food can become contaminated in different ways.

Some bacteria and parasites can be reduced or destroyed through appropriate cooking.

Certain surface contaminants can be reduced through proper washing and handling.

Mercury is different because it accumulates inside the fish's tissues.

Once methylmercury has entered the fish through its diet, ordinary kitchen preparation cannot remove it.

This means that a swordfish steak does not become a low-mercury meal simply because it is grilled at a high temperature.

Likewise, deep-frying a high-mercury fish does not make it suitable for pregnant women or young children.

The most effective approach is choosing a lower-mercury species before preparing the meal.

Why repeated exposure matters

Mercury exposure is generally a concern related to the amount consumed over time.

The human body can eliminate some mercury naturally, but this process is relatively slow.

Repeatedly eating high-mercury fish can increase the amount present in the body.

This is particularly relevant for people who consume the same large predatory species several times each week.

For example, a family might purchase large fish steaks because they are convenient and easy to prepare.

If those steaks repeatedly come from high-mercury species, the family could receive more methylmercury exposure than intended.

Choosing different lower-mercury species helps reduce this concern.

Why children need smaller portions

Children should not automatically receive the same seafood portions as adults.

Their serving sizes should reflect their age, body weight, and nutritional needs.

The FDA provides the following approximate serving sizes for children:

These are general FDA recommendations for fish from the Best Choices category, not instructions to serve every child the same amount regardless of individual circumstances.

Is one meal containing high-mercury fish dangerous?

Many people become worried after discovering that they have eaten swordfish, shark, or another high-mercury species.

However, the FDA explains that eating one serving of a fish from the Choices to Avoid category does not automatically mean a person will become ill.