In 30 seconds
- Only four species are high in mercury: swordfish, bluefin tuna, shark and pike.
- Pregnant and breastfeeding women and children under 10 should avoid them; from 10 to 14, no more than 120 g a month.
- For everyone, AESAN recommends 3-4 portions of fish a week, alternating white and oily fish.
- Cooking fish or removing the skin does not reduce mercury. In omega-3 supplements, it is removed when the oil is purified.
If you look after yourself and train, fish and tinned tuna probably appear on your menu several times a week. Mercury is the reason many people limit them unnecessarily. The key is not to eat less fish, but to choose the right ones.
Why some have more
How mercury builds up in fish
Why some have more than others
Mercury reaches the sea and builds up in fish as methylmercury. Large predatory fish, which live for many years and eat other fish, accumulate much more. Small ones, such as anchovies or sardines, very little.
Which fish have more and which have less
| Content | Species |
|---|---|
| High | Swordfish, bluefin tuna, shark (tope, mako, spiny dogfish, small-spotted catshark, blue shark) and pike |
| Low | Anchovy, herring, cod, mackerel, horse mackerel, hake, salmon, sardine, trout, gilthead bream, sea bass, sole, squid, octopus, cuttlefish, prawn, king prawn, mussel, clam and cockle, among others |
| Medium | The rest, such as tuna other than bluefin, bonito or monkfish |
Source: AESAN, recommendations on fish consumption due to the presence of mercury.
Anything that does not appear on either list has a medium content 1.
How much fish to eat
AESAN's figures
How much fish to eat
For the whole population, AESAN, Spain's food safety agency, recommends 3-4 portions of fish a week, alternating between white and oily fish 1. What changes depending on who you are is how much you eat of the four species highest in mercury:
| Who | Fish high in mercury | Other fish |
|---|---|---|
| Pregnant, breastfeeding or trying to conceive | Avoid | 3-4 portions a week |
| Children up to 10 | Avoid | 3-4 portions a week |
| Children aged 10 to 14 | 120 g a month at most | 3-4 portions a week |
| Everyone else | No specific limit, varying species | 3-4 portions a week |
Source: AESAN.
As reported by Eroski Consumer, a Spanish consumer magazine, EFSA concluded that, when fish is eaten as part of a varied and balanced diet, the benefits far outweigh the risks 2.
Myths
What people believe and what happens with mercury
Myths worth dispelling
- “If I cook it, the mercury goes.” No. It is in the flesh of the fish and does not change when you boil, fry or grill it 2.
- “Removing the skin and fat gets rid of it.” No again: mercury is in the muscle, not in the fat 2.
- “Tinned fish has more.” Mercury depends on the species, not on whether the fish is fresh, frozen or tinned, nor on whether it is in oil or in brine 2.
And tinned tuna?
Tinned tuna does not use bluefin, but smaller tuna species. According to the calculations reported by Eroski Consumer, a 60 kg person would reach their limit at about 10 small tins a week 2. There is no need to give it up, but it should not be your only fish either. It also provides much less omega-3 than small oily fish.
And omega-3 supplements?
According to the US NIH, no mercury has been found in omega-3 supplements, because it is removed when the oil is processed and purified 3.
Our Anchovy Omega-3 is made from anchovy oil, one of the species lowest in mercury according to AESAN 1, and provides 900 mg of EPA and DHA in 3 softgels. If you want to know whether your fish already gives you enough, try our omega-3 calculator.
Frequently asked questions
Which fish has the most mercury?
Swordfish, bluefin tuna, shark (tope, mako, spiny dogfish, small-spotted catshark and blue shark) and pike. They are large predatory fish that accumulate more mercury over their lifetime.
Which fish has the least mercury?
According to AESAN, among others: anchovy, sardine, mackerel, horse mackerel, herring, salmon, trout, hake, cod, gilthead bream, sea bass, sole and most shellfish.
How many tins of tuna can you eat a week?
Tinned tuna does not use bluefin, but smaller tuna species with less mercury. According to the calculations reported by Eroski Consumer, a 60 kg person would reach their limit at about 10 small tins a week. Even so, it is better to vary.
Do omega-3 supplements contain mercury?
According to the US NIH, no mercury has been found in omega-3 supplements, because it is removed when the oil is processed and purified.
Sources
- AESAN. Recommendations on fish consumption due to the presence of mercury. View publication
- Eroski Consumer. Pescado y mercurio: todo lo que debes saber. 2021. View publication
- Office of Dietary Supplements, National Institutes of Health. Omega-3 fatty acids: fact sheet for health professionals. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product. A varied and balanced diet and a healthy lifestyle are important.
