Your weekly limit is set by body weight
The mercury in a meal is the fish's concentration times how much you eat: a 170 g (6 oz) serving of a 0.3 µg/g fish is about 50 µg of mercury. Compare that to your weekly allowance. A 60 kg adult gets about 42 µg a week, so one such serving already uses most of it. Lighter people and children get proportionally less.
Mercury by fish, and how it groups
| Fish | Mercury (µg/g) | FDA group |
|---|---|---|
| Scallops | 0.003 | Best choice |
| Shrimp | 0.009 | Best choice |
| Sardines | 0.013 | Best choice |
| Salmon | 0.017 | Best choice |
| Skipjack (light) tuna | ~0.05 | Best choice |
| Cod | 0.111 | Best choice |
| Halibut | 0.241 | Good, once a week |
| Yellowfin tuna | ~0.27 | Good, once a week |
| King mackerel | ~0.73 | Avoid |
| Shark | 0.98 | Avoid |
| Swordfish | 0.99 | Avoid |
| Tilefish | ~1.15 | Avoid |
Best choices sit at or below 0.15 µg/g and support 2 to 3 servings a week; "avoid" fish clear 0.46 µg/g. Big, long-lived predators concentrate the most because mercury builds up the food chain.
Weekly allowance by body weight
| Body weight | Safe mercury / week | Roughly equals |
|---|---|---|
| 20 kg (child) | 14 µg | ~800 g of salmon |
| 40 kg | 28 µg | 1–2 servings of yellowfin tuna |
| 60 kg | 42 µg | ~1 serving of a 0.3 µg/g fish |
| 80 kg | 56 µg | less than 1 serving of shark |
Pregnant women and children under 11 should treat these as ceilings, not targets, and skip the "avoid" list. Methylmercury has a 50 to 70 day half-life, so it clears slowly and regular exposure matters more than a one-off meal.
Common questions
How much methylmercury is safe to eat per week?
The EPA reference dose is 0.1 microgram per kilogram of body weight per day. For a 60 kg adult that is 6 micrograms a day, or about 42 micrograms across a week. Children and pregnant women should stay well under it because the developing brain is more sensitive.
Which fish are highest in mercury?
Shark, swordfish, king mackerel, tilefish, marlin and bigeye tuna carry the most, roughly 0.5 to 1 microgram per gram. The FDA advises pregnant women and young children avoid these entirely. Salmon, sardines, shrimp and tilapia are among the lowest.
Does the omega-3 in fish cancel out the mercury?
No. Omega-3 has real heart and brain benefits but it does not remove or neutralise mercury; they are separate issues. The practical answer is to pick fish that are high in omega-3 and low in mercury, such as salmon and sardines.
