Mercury in fish: which ones, and how often
Fish is among the best things you can eat and four species are worth avoiding outright. The rule is simple once you know it runs on size and lifespan.
Fish is one of the few foods where nearly every authority agrees people should eat more of it. It is also the food carrying the most persistent contaminant concern. Both are true, and the resolution is straightforward once you know the rule.
The rule: bigger and older means more
Methylmercury accumulates up the food chain. A large predator that lives for decades eating smaller fish concentrates everything those fish accumulated.
So mercury tracks almost perfectly with size and lifespan:
- A sardine lives about five years and eats plankton. Very low.
- A swordfish lives fifteen-plus years and eats other predators. Very high.
Once you know that, you can classify an unfamiliar fish without a chart.
The avoid list
Short, and worth memorizing:
Shark · Swordfish · King mackerel · Tilefish
Plus bigeye tuna, marlin and orange roughy in most versions of the advice.
The FDA and EPA say to avoid these entirely during pregnancy, when breastfeeding, and for young children. For other adults, rare is fine; this is about accumulation, not a single meal.
The eat-freely list
Much longer, and it covers most of what is actually in a supermarket:
Salmon · sardines · anchovies · trout · herring · mackerel (Atlantic, not king) · tilapia · cod · pollock · haddock · catfish · shrimp · scallops · oysters · mussels · squid · canned light tuna
Two to three servings a week of these is the recommendation, not the limit.
The tuna distinction
Tuna causes most of the confusion because "tuna" covers several species with very different profiles:
| Type | Mercury | Guidance |
|---|---|---|
| Canned light (skipjack) | Low | 2–3 servings/week |
| Albacore / white | Moderate, about 3× light | About 1 serving/week |
| Yellowfin | Moderate | About 1 serving/week |
| Bigeye (steaks, sashimi) | High | Avoid |
The cheap can is the safe one. The expensive steak is the one to limit.
Why the benefit usually wins
It is worth being clear that the net advice is eat more fish, not less.
The omega-3 fatty acids EPA and DHA have solid evidence behind them for cardiovascular and neurological outcomes, and oily fish is by far the most reliable source. Large analyses consistently find that for most people the benefit of eating low-mercury fish regularly outweighs the mercury risk by a wide margin.
The exception is the group where developing nervous systems are involved, pregnancy, breastfeeding, young children, and even there the advice is to eat 8–12 oz a week of low-mercury fish: not to avoid fish.
The message is not "fish is risky". It is "four species are, and the rest are among the best things on the menu".
Common questions
- Which fish are highest in mercury?
- Shark, swordfish, king mackerel, tilefish, bigeye tuna, marlin and orange roughy. The FDA and EPA advise avoiding these entirely during pregnancy and for young children.
- Which fish are lowest in mercury?
- Salmon, sardines, anchovies, trout, herring, tilapia, cod, pollock, shrimp, scallops, oysters and canned light tuna. These can be eaten two to three times a week, which is what the guidance actively encourages.
- Is canned tuna safe to eat?
- Canned light tuna, usually skipjack, is low enough for two to three servings a week. Albacore or white tuna is roughly three times higher and is limited to about one serving a week. Bigeye tuna, sold as steaks and sashimi, is on the avoid list.
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