Mercury in fish can be a real health concern because the metal builds up in aquatic food chains and concentrates in larger, longer‑lived species. While fish remains a nutritious choice for many people, experts advise selecting species carefully and adjusting consumption for vulnerable groups, including those who are pregnant, trying to conceive, breastfeeding, infants and young children.
How mercury gets into seafood
Mercury enters waterways through natural processes and human pollution. Once in lakes, rivers or the sea, it is taken up by small organisms and then moves up the food chain: small fish absorb minute amounts and are eaten by larger predators, which in turn accumulate more mercury over time. This process, known as biomagnification, is why top predators tend to have the highest concentrations of mercury.
Who should be most cautious?
Registered dietitians and public‑health authorities emphasise that occasional fish consumption is unlikely to harm most healthy adults because the body can eliminate low amounts of mercury. However, the developing brains and nervous systems of fetuses, infants and young children are more vulnerable to damage from higher mercury exposure. For that reason, people who are pregnant, planning pregnancy or breastfeeding should take extra care to minimise intake.
"Size matters here," said registered dietitian Julia Zumpano, underscoring that larger, longer‑lived fish generally carry more mercury.
Species to avoid or limit
The US Food and Drug Administration classifies several commonly consumed species as higher‑mercury and advises limiting or avoiding them. The list includes:
- Bigeye tuna
- King mackerel
- Marlin
- Orange roughy
- Shark
- Swordfish
- Tilefish
Choosing smaller, shorter‑lived species reduces the likelihood of higher mercury intake. For many people this approach preserves the health benefits of eating fish while lowering exposure to the toxic metal.
Practical tips for safer fish consumption
- Prefer smaller, short‑lived species whenever possible; these generally contain less mercury than apex predators.
- Limit consumption of the high‑mercury species listed above, especially for pregnant and breastfeeding people and young children.
- Maintain variety in your seafood choices to avoid concentrating mercury intake from a single species.
- If uncertain about local contamination levels (for example, in freshwater fisheries), check guidance from regional environmental or health authorities.
| Risk category | Examples |
|---|---|
| Higher mercury | Bigeye tuna; King mackerel; Marlin; Orange roughy; Shark; Swordfish; Tilefish |
| Lower mercury | Smaller, shorter‑lived species (consult local guidance for specifics) |
Health professionals caution against removing fish from the diet entirely: many types of seafood provide valuable nutrients such as omega‑3 fatty acids, protein and vitamins. The key is balancing those benefits against the risk of mercury exposure by choosing species wisely and moderating portions for groups at greater risk.
If you have specific concerns about mercury and your diet — for example, if you are pregnant, breastfeeding, trying to conceive, or feeding young children — speak with your doctor, clinic or a registered dietitian for personalised advice tailored to your health needs and local seafood availability.
Note: This article summarises expert guidance and an overview of species identified by the US Food and Drug Administration as typically higher in mercury. For detailed, region‑specific recommendations consult your provincial health department or environmental authority.
