About Mercury in Fish and Shellfish

About Mercury in Fish and Shellfish

Fish and shellfish are widely praised for their high-quality protein, omega-3 fatty acids, vitamins, and minerals. Regular seafood consumption is linked to better heart health, brain function, and reduced inflammation. However, concerns about mercury—especially methylmercury—often cause confusion and fear. Understanding how mercury ends up in seafood, which fish are riskier, and how to eat fish safely is key to getting the benefits without unnecessary risk.

What Is Mercury, and How Does It Enter Seafood?

Mercury is a naturally occurring element found in the Earth’s crust. It is released into the environment through natural processes such as volcanic activity and through human activities like coal burning, mining, and industrial pollution. Once mercury enters rivers, lakes, and oceans, microorganisms convert it into methylmercury, a highly toxic form that easily accumulates in living organisms.

Fish absorb methylmercury from the water and from the organisms they eat. Small fish contain small amounts, but larger predatory fish accumulate much higher levels over time. This process, known as biomagnification, explains why top predators tend to have the highest concentrations of mercury.

Why Mercury Is a Health Concern

Methylmercury is particularly harmful to the nervous system. In adults, high exposure can affect memory, coordination, vision, and fine motor skills. Long-term exposure may also impact cardiovascular health.

The greatest concern is for pregnant women, breastfeeding mothers, and young children. Mercury can cross the placenta and interfere with the development of the fetal brain and nervous system. Even moderate exposure during pregnancy may affect learning, attention, and motor skills in children.

That said, mercury poisoning from seafood is rare when people follow established dietary guidelines.

Fish High in Mercury

Some fish consistently show higher mercury levels due to their size, age, and position in the food chain. These are best avoided or eaten very rarely, especially by vulnerable groups.

Shark

Swordfish

King mackerel

Tilefish (especially from the Gulf of Mexico)

Bigeye tuna

These species are long-lived predators and accumulate mercury over many years.

Fish and Shellfish Low in Mercury

Many commonly eaten fish and shellfish are naturally low in mercury and can be eaten regularly

Salmon

Sardines

Anchovies

Trout

Herring

Cod

Pollock

Tilapia

Shrimp

Crab

Lobster

Oysters, mussels, and clams

Shellfish generally contain lower mercury levels because they are short-lived and feed low on the food chain.

Balancing Benefits and Risks

Fish remains one of the healthiest protein sources available. The omega-3 fatty acids DHA and EPA support heart health, reduce triglycerides, and play a critical role in brain function. For pregnant women, omega-3s are essential for fetal brain and eye development.

Health authorities around the world agree that the benefits of eating low-mercury fish far outweigh the risks. The key is choosing the right species and moderating intake of higher-mercury fish.

How Much Fish Is Safe to Eat?

General guidelines for adults recommend:

2–3 servings per week (about 200–350 grams total) of low-mercury fish

For pregnant or breastfeeding women

2 servings per week of low-mercury fish

Avoid high-mercury species completely

Children should eat smaller portions based on body weight, focusing on low-mercury options.

Does Cooking Reduce Mercury?

Cooking, freezing, or cleaning fish does not significantly reduce mercury levels. Mercury is stored in the muscle tissue, not in the skin or fat. This means safety depends on fish choice and portion size—not preparation method.

Practical Tips for Safe Seafood Consumption

Rotate fish types instead of eating the same species repeatedly

Choose smaller fish rather than large predators

Limit canned tuna intake, especially albacore (white tuna)

Prefer wild or responsibly farmed fish from clean waters

Follow local advisories for freshwater fish if you fish yourself

The Bottom Line

Mercury in fish and shellfish is a real but manageable concern. It does not mean you should avoid seafood altogether—in fact, doing so may deprive your body of vital nutrients. By choosing low-mercury species, eating a varied diet, and following established guidelines, you can enjoy the nutritional benefits of fish while keeping mercury exposure well within safe limits.