For most adults, two to three servings of fish per week is the sweet spot, and consistently eating more than that requires careful attention to which fish you’re choosing. A standard serving is 4 ounces (about the size of your palm), which means the general target is 8 to 12 ounces of fish per week. Go beyond that with high-mercury species, and you risk accumulating a neurotoxin that your body clears slowly.
The Weekly Limits by Fish Type
Not all fish carry the same risk, so “too much” depends entirely on what’s on your plate. The EPA and FDA divide fish into three tiers based on mercury content, and each tier comes with its own ceiling.
- Best Choices (lowest mercury): Salmon, shrimp, crab, lobster, scallops, oysters, canned light tuna, tilapia, cod, and sardines. You can safely eat two to three servings per week from this group.
- Good Choices (moderate mercury): Albacore (white) tuna, snapper, grouper, and halibut. Limit yourself to one serving per week, and don’t eat other fish that week.
- Choices to Avoid (highest mercury): Shark, swordfish, king mackerel, bigeye tuna, marlin, orange roughy, and Gulf of Mexico tilefish. These accumulate so much mercury that no safe weekly serving exists for regular consumption.
If you weigh less than about 165 pounds, the standard advice is slightly generous for your body size. Sticking to two servings from the Best Choices list, or choosing smaller portions, keeps your mercury exposure within safe margins.
Why Mercury Builds Up
Mercury enters waterways from both natural sources and industrial pollution. Bacteria in the water convert it into methylmercury, a form that fish absorb and struggle to eliminate. Larger, longer-lived predatory fish sit at the top of the food chain, so they accumulate mercury from every smaller fish they eat over their lifetimes. A swordfish that has been alive for a decade carries vastly more mercury than a sardine that lives for a year or two.
Your body processes methylmercury slowly. If you eat high-mercury fish regularly, it builds up faster than you can clear it. Over time, this can lead to tremors, memory loss, insomnia, headaches, and problems with coordination and motor control. These symptoms reflect damage to the nervous system, which is particularly sensitive to methylmercury. For most adults eating a reasonable amount of lower-mercury fish, toxicity is unlikely. The risk rises when people eat large predatory fish frequently, sometimes daily, over months or years.
The Tuna Question
Tuna is the fish most people wonder about, and the answer splits along species lines. Canned light tuna (usually skipjack) contains meaningfully less mercury than canned albacore (white) tuna. You can include light tuna in your regular two-to-three servings of Best Choices fish without special concern. Albacore tuna falls into the Good Choices tier, so it should be limited to one serving per week with no other fish that week.
Bigeye tuna, the kind often served as sushi or sashimi in restaurants, lands in the Choices to Avoid category entirely. If you eat sushi regularly, it’s worth asking what species of tuna you’re getting.
Shellfish Are the Safest Bet
Shrimp, crab, lobster, scallops, oysters, and crayfish all fall into the lowest mercury category. None of them appear on any high-mercury list. If you love seafood and want to eat it frequently, shellfish gives you the most room. Adults outside of vulnerable groups can eat up to four meals per week of low-mercury seafood without concern.
Pregnancy and Children
Mercury is most dangerous to developing brains, which is why the limits tighten for pregnant and breastfeeding women and for young children. Pregnant women should eat 8 to 12 ounces per week of lower-mercury fish, sticking to the Best Choices list. Fish in the Choices to Avoid category is off the table entirely during pregnancy and breastfeeding.
Children need smaller portions scaled to their size: roughly 1 ounce per serving for ages one to three, 2 ounces for ages four to seven, 3 ounces for ages eight to ten, and a full 4-ounce adult serving by age eleven. Two servings per week from the Best Choices list is the target. Parents should avoid serving shark, swordfish, bigeye tuna, or king mackerel to children at any age.
For albacore tuna specifically, Health Canada advises that children ages five to eleven can have about one can per week, and children ages one to four should have no more than half a can.
Benefits Still Outweigh Risks for Most People
Fish is one of the best dietary sources of omega-3 fatty acids, which support heart health, brain function, and fetal development. The Mayo Clinic’s position is clear: for most adults, the benefits of eating fish as part of a healthy diet outweigh the risks from contaminants. The goal isn’t to avoid fish. It’s to choose wisely.
There’s also an interesting wrinkle involving selenium, a mineral found naturally in many fish. Research dating back to the 1960s has shown that selenium can reduce mercury’s toxic effects in the body. Some scientists argue that the ratio of selenium to mercury in a given fish is a better predictor of risk than the mercury level alone. Most fish that are high in selenium relative to mercury (like salmon and sardines) are already on the Best Choices list, so the practical takeaway aligns with existing guidelines.
Mercury Isn’t the Only Contaminant
Mercury gets the most attention, but fish can also carry persistent organic pollutants like PCBs and dioxins. These compounds accumulate in fatty tissue over time and are classified as probable human carcinogens. At high exposure levels, they’ve been linked to skin disorders, liver damage, and developmental problems in children.
For most commercially sold fish, contamination levels are monitored and kept within safety limits. The risk is higher with recreationally caught fish from polluted lakes or rivers. If you catch your own fish, check local advisories for the specific body of water. These advisories account for contaminants that commercial testing covers at the point of sale.
A Practical Upper Limit
Pulling the numbers together: if you’re eating exclusively from the lowest-mercury fish, four servings a week (about 16 ounces) appears safe for most adults who aren’t pregnant. If you’re mixing in moderate-mercury fish like albacore tuna or snapper, cap those at 4 ounces total per week and keep them as your only fish for that week. If any high-mercury species makes it onto your plate, treat it as a rare occasion, not a habit.
The simplest rule: eat fish twice a week, favor small and short-lived species, and treat swordfish, shark, and bigeye tuna as foods you encounter occasionally rather than stock in your kitchen. That approach lands you squarely in the range where fish protects your health rather than threatening it.