Mercury in Fish: What You Need to Know
Mercury is a heavy metal that reaches oceans and seas through both natural processes and human activities, including industrial pollution. In the water, certain bacteria transform mercury into methylmercury, its most toxic form.
This methylmercury enters the food chain when tiny marine organisms and plankton absorb it. Small fish eat the contaminated plankton, larger fish eat the smaller fish, and so on. Over time, mercury accumulates in the bodies of these predators. As a result, the bigger and older the fish, the higher its mercury concentration is likely to be.
Top Fish High in Mercury
The following types of fish are known to contain elevated levels of mercury and should be eaten rarely or avoided, especially by vulnerable groups such as pregnant women and young children.
Shark
Sharks are long-lived top predators that feed on many smaller fish. This gives them extremely high levels of mercury compared with most other seafood.
Frequent consumption of shark may increase the risk of neurological damage and mercury poisoning.
Swordfish
Swordfish is a large predatory species well known for its very high mercury content.
Health authorities generally recommend that pregnant women, women who may become pregnant, and children avoid swordfish entirely.
Bigeye and Yellowfin Tuna
Not all tuna is the same in terms of mercury. While canned light tuna typically contains lower mercury levels, bigeye tuna and yellowfin tuna tend to be much higher.
Regularly eating these large tuna species can significantly increase mercury intake.
King Mackerel
King mackerel is among the most heavily contaminated fish when it comes to mercury. Because of its high levels, it is not considered safe for frequent consumption.
Tilefish
Tilefish caught in areas such as the Gulf of Mexico are among the species with the highest mercury concentrations.
Due to this risk, many guidelines advise avoiding tilefish, particularly for children and pregnant women.
Health Risks of High-Mercury Fish
Consuming fish with high levels of mercury can lead to serious health problems, especially when eaten often or over a long period. Potential risks include:
- Damage to the nervous system, with the greatest impact on developing brains in fetuses and young children
- Impaired kidney and liver function from mercury buildup in the body
- Problems with memory, focus, and concentration in adults
- Disorders affecting the digestive and immune systems
Healthier Low-Mercury Fish Options
Many types of seafood are rich in protein and omega-3 fatty acids yet naturally low in mercury. These are generally safer choices for regular meals:
- Salmon
- Sardines
- Anchovies
- Tilapia
- Cod
Including these low-mercury fish in your diet can help you gain the benefits of seafood while minimizing mercury exposure.
Tips for Buying and Eating Fish Safely
To reduce your mercury intake while still enjoying seafood:
- Choose smaller fish instead of large predatory species, as they usually contain less mercury.
- Avoid high-mercury fish during pregnancy, while breastfeeding, and for young children.
- Limit high-mercury fish to no more than once a month, if you choose to eat them at all.
- Follow official guidance from agencies such as the FDA and EPA for up-to-date recommendations on safe fish consumption.
