Mercury in Fish: How to Choose Seafood Lower in Mercury
A tin of sardines and a swordfish steak both contain mercury. What separates them is how much mercury each serving carries and how many servings you eat in a week. For anyone choosing fish during pregnancy or for children, the main U.S. source is the FDA and EPA’s Advice about Eating Fish, revised October 2021.
Why big, long-lived predators carry more
Nearly all fish contain at least traces of methylmercury, and fish take it in through the food they eat. It tends to build up more in some types of fish than others, especially in larger fish that eat other fish and those fish that live longer. Think of a jar that only fills and is almost never emptied. Each meal adds a little. A predator that lives for years and eats many smaller fish keeps adding to its load the whole time. That explains why the “avoid” list is mostly large ocean hunters.
The agencies focus on pregnancy and early childhood because of mercury’s potential effect on developing brains.
How does the FDA/EPA advisory decide which fish are safe?
The categories come from a calculation. FDA says it took a cautious and highly protective approach. Using mercury data for each type of fish, it worked out how many servings an average pregnant person could eat in a week. Fish that could be eaten at least three times a week became “Best Choices.” Fish safe only once or twice a week became “Good Choices.” Fish that couldn’t be eaten even once a week became “Choices to Avoid.” The agency’s technical document gives the cutoff: any fish averaging 0.15 µg/g of mercury or less counts as a Best Choice. Altogether, the chart rates more than 60 different fish.
| Category | Mercury basis | Weekly servings (pregnancy) | Examples |
|---|---|---|---|
| Best Choices | Average ≤0.15 µg/g (fda.gov) | 2–3 (fda.gov) | Salmon, sardines, shrimp, pollock (fda.gov) |
| Good Choices | Average ≤0.46 µg/g (fda.gov) | 1 (fda.gov) | Halibut, snapper, grouper, albacore and yellowfin tuna (fda.gov) |
| Choices to Avoid | Not safe even once a week (fda.gov) | None | Shark, swordfish, king mackerel, tilefish (Gulf of Mexico), orange roughy, marlin, bigeye tuna (pmc.ncbi.nlm.nih.gov) |
The full avoid list has seven fish: shark, swordfish, king mackerel, tilefish from the Gulf of Mexico, orange roughy, marlin, and bigeye tuna. FDA’s Good Choices list (one serving a week) is bluefish, buffalofish, carp, Chilean sea bass/Patagonian toothfish, grouper, halibut, mahi mahi, monkfish, rockfish, sablefish, sheepshead, snapper, Spanish mackerel, striped bass (ocean), tilefish (Atlantic Ocean), albacore and yellowfin tuna, weakfish/seatrout, and white croaker/Pacific croaker.
Safe fish servings each week for pregnant women and children
During pregnancy and breastfeeding, 1 serving is 4 ounces, or about the size of your palm. The guidance is two to three servings a week from Best Choices, or one from Good Choices. That lines up with the Dietary Guidelines’ range of 8 to 12 ounces per week. The math assumes an adult who weighs 165 pounds. If you weigh less, FDA suggests smaller portions, such as 2.5 ounces three times a week or 4 ounces two times a week.
Children should eat 2 servings a week from the “Best Choices” list, with serving sizes that grow with age:
| Age | Average serving (fda.gov) |
|---|---|
| 1 to 3 | 1 ounce |
| 4 to 7 | 2 ounces |
| 8 to 10 | 3 ounces |
| 11 | 4 ounces |
There’s a catch. For some children, the Dietary Guidelines recommend more fish than the FDA/EPA mercury limits allow. FDA’s answer is a group of 22 fish within “Best Choices” that are even lower in mercury. These include anchovies, Atlantic mackerel, catfish, clams, crab, flounder, haddock, oysters, salmon, sardines, shrimp, tilapia, and trout, among others.
Local advisories: fish the national chart doesn’t cover
The national chart is based on fish sold in stores. A perch from the lake down the road is a different case. For fish caught by family or friends, check for fish and shellfish advisories; if there is none, eat only one serving and no other fish that week. Some waters have had little or no monitoring, and fish caught for sport or food can contain higher levels of mercury than commercially available species. Fish such as larger carp, catfish, trout and perch are more likely to have advisories. Before cooking fish you catch yourself, FDA recommends removing skin, fat, and internal organs, where other pollutants can collect.
Why the agencies still want you to eat fish
FDA asks itself whether people should skip fish to avoid mercury. Its answer is no. Fish supply omega-3s (DHA and EPA), iron, iodine during pregnancy, and choline, and moderate scientific evidence links eating fish during pregnancy to better cognitive development in babies. Even so, seafood consumption among maternal and child populations remains low.
The advice has also shifted in direction. The 2004 version set a cap: pregnant women could eat 12 oz of fish weekly, but they could also adhere to the advice by eating little or no fish. The revised advice, first drafted in 2014 and finalized in 2017, added a minimum, encouraging consumption of 8 to 12 ounces of a variety of fish per week to maximize the potential benefits that fish could provide.
A commentary in PMC argues the risk is still overstated. It cites a Seychelles study that followed mothers and children 10 times during a 24-year period and found no harm to development, even though prenatal exposure was more than 10 times the typical levels in the United States. It also cites a UK study of cord blood from 1054 mothers and a Spanish study of 1683 children. These are observational studies. They show the absence of an association, not proof that no child could ever be harmed. The same authors also agree the seven high-mercury fish should be avoided.
| Date | Event | Impact |
|---|---|---|
| 2004 | Original advice (federalregister.gov) | 12 oz weekly cap; four fish to avoid |
| Aug 2016 | External peer review of method (federalregister.gov) | Shaped the revised categories |
| Jan 2017 | Revised advice issued (federalregister.gov) | Recommends consuming 8–12 oz (2–3 servings) a week (pmc.ncbi.nlm.nih.gov) |
| May 2017 | Petition to withdraw advice (pmc.ncbi.nlm.nih.gov) | Asked for a focus on benefits |
| Oct 2017 | FDA denies petition (pmc.ncbi.nlm.nih.gov) | Advice stands |
| Nov 2017 | Petitioners ask FDA to reconsider (pmc.ncbi.nlm.nih.gov) | — |
| Oct 2021 | Advice revised (fda.gov) | Updated for the Dietary Guidelines 2020–2025, including children under age 2 (fda.gov) |
In practice, the advice comes down to a few steps. Eat fish regularly, mix up the types, and choose mostly from Best Choices. Leave out the seven high-mercury fish. Check a local advisory before eating fish someone caught.
Sources
- fda.gov – “Questions & Answers from the FDA/EPA Advice about Eating Fish for Those Who Might Become or Are Pregnant or Breastfeeding and Children Ages 1 to 11 Years | FDA” (2024)
- federalregister.gov – “Federal Register :: Advice About Eating Fish, From the Environmental Protection Agency and Food and Drug Administration; Revised Fish Advice; Availability” (2017)
- fda.gov – “Advice about Eating Fish | FDA” (2024)
- pmc.ncbi.nlm.nih.gov – “Fish Consumption During Pregnancy” (2018)
- epa.gov – “EPA-FDA Advice about Eating Fish and Shellfish | US EPA” (2015)
- fda.gov – “Technical Information on Development of FDA/EPA Advice about Eating Fish for Those Who Might Become or Are Pregnant or Breastfeeding and Children Ages 1-11 Years | FDA” (2024)