Mercury in Fish: Should You be Concerned?

Mercury is mainly present in large bluefish. Pregnant women and children should be particularly wary of how much of this type of fish they consume. Continue reading to find out more.
Mercury in Fish: Should You be Concerned?

Last update: 16 January, 2020

Nearly everyone knows that there are many health benefits to eating fish due to its high contribution of unsaturated fatty acids. However, there’s growing concern about the risks of mercury in fish.

In today’s article, you’ll find out if the mercury contained in fish is truly dangerous, what’s the safe amount you can consume, and which varieties have it in larger quantities.

Mercury in fish

Mercury occurs naturally in the soil, water, plants, and animals. The problem is that human activity contributes large amounts of mercury to the environment through the incineration of solid waste, the use of fossil fuels, and the use of mercury in all sorts of industries.

Mercury goes into fish through the food they eat, so the most predatory fish – which are also the largest – accumulate larger amounts of it.

Risks of consuming fish with mercury

The toxicity of mercury depends on its chemical form, type, amount and age of exposure. Of all the chemical types of mercury present in food, the organic methylmercury compound is the most toxic one. This kind is largely present in fish and shellfish.

This chemical compound can affect the kidneys and central nervous system, especially during fetal development, by crossing both the blood-brain barrier and the placenta. It can also cause alterations in the normal brain development of infants. Plus, at higher doses, it can even induce neurological changes in adults.

What fish contains mercury?

Half a bluefish.

Certain varieties of fish have a higher concentration of mercury. Big fish typically have the most.

Overall, the highest concentrations of mercury are found in freshwater and saltwater fish, particularly in the large species which are part of the highest level of the food chain, such as the following:

Big-eyed tuna

Tuna contains the most alarming amounts of mercury. However, it isn’t Mediterranean tuna you should worry about, but large-eyed tuna. This variety of tuna inhabits tropical and subtropical areas of the Atlantic, Indian and Pacific.


Swordfish is one of the commercial fish with the highest amounts of mercury. It’s a predator that consumes large amounts of fish daily. Therefore, it absorbs all of the mercury its prey contains. Then, the mercury it contains ends up on your body.


This species also has high percentages of mercury. Sharks can be as small as a dwarf lantern shark to as big as a whale shark. Either way, since they’re predators, they absorb a lot of mercury from their prey.


The pike is a large predator, which feeds on all sorts of species that include crab. It’s an invasive species in some parts of the world.

How much fish can you eat without risk?

A plate of fish, potatoes and asparagus.

For safe fish consumption, you should limit your intake of varieties identified as having high levels of mercury. In addition, you should avoid them if you’re pregnant.

The World Health Organization recommends limiting your intake of bluefin tuna, swordfish, shark and pike. However, you must take the origin of the meat into account, as some waters are more polluted than others. The Joint FAO and WHO Expert Committee on Food Additives reviewed the tolerable weekly intake for methylmercury in June 2003, reducing it from 3.3 μg/kg body weight to 1.6 μg/kg body weight.

AESAN recommendations for risk groups are as follows:

  • Children under 3 years should avoid its consumption
  • For children between 3-12 years old, you must limit their intake to 50 g/week or 100 g/2 weeks (They shouldn’t consume any other fish in this category in the same week).

Recommendations on fish consumption

Fish is essential for a balanced diet since it provides proteins of high biological value such as vitamins A, D, and B12, iodine and selenium. A diet containing fish and shellfish will help maintain your cardiovascular health. Similarly, there’s no evidence of a relationship between mercury intake and risk of coronary heart disease.

Taking into account the benefits provided by DHA fatty acids and weighing them against the risk of mercury, the consumption of fish by women of childbearing age or pregnant or breastfeeding reduces the risk of abnormal neurological development of children.

The fundamental thing is to alternate the types of fish you consume.

  • Opt for other types of blue fish such as sea bass, sea bream, salmon, sardines, trout, etc.
  • Healthy adults shouldn’t consume fish that’s high in mercury such as tuna, swordfish, pike or shark more than once a week.
  • Avoid eating canned tuna too frequently. In one study, researchers examined university students who ate it often and they had a higher level of mercury in their hair than those who didn’t eat this kind of food.
  • You should alternate between eating bluefish and whitefish, as the latter contains less mercury.

In conclusion

High concentrations of mercury in certain varieties of fish are enough to limit their intake. Its consumption might be responsible for an increased risk of health problems. Likewise, it’s important to remember that other varieties of fish are still very healthy.

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  • Rhee JJ., Kim E., Buring JE., Kurth T., Fish consumption, omega 3 fatty acids, and risk of cardiovascular disease. Am J Prev Med, 2017. 52 (1):  10-19.
  • Bjorklund G., Tinkov AA., Dadar M., Rahman M., et al., Insights into the potential role of mercury in alzheimer’s disease. J Mol Neurosci, 2019. 67 (4): 511-533.