Is It Safe to Eat Swordfish? What You Need to Know

Swordfish is safe to eat in moderation for most adults, but it consistently ranks among the highest-mercury fish available at the market. That distinction matters because the mercury in swordfish is almost entirely methylmercury, the organic form that your body absorbs efficiently and clears slowly. For pregnant women, nursing mothers, and young children, most health agencies recommend avoiding swordfish altogether. For everyone else, the practical question is not whether swordfish is dangerous in a single serving, but how often you can eat it before the mercury exposure starts to outweigh the nutritional benefits.

Why Swordfish Carries So Much Mercury

Mercury enters the ocean primarily from natural sources like volcanic activity and from human sources like coal-fired power plants. Once in the water, microorganisms convert it to methylmercury, which enters the food chain at the bottom and becomes more concentrated at each step. Swordfish sit near the top of open-ocean food webs, and they live long lives, sometimes exceeding a decade. Every meal they eat adds to their mercury load, and they eliminate it slowly. The result is that a large adult swordfish has had years to accumulate mercury from thousands of smaller fish and squid.

Research on mercury in oceanic predators confirms swordfish as one of the more contaminated species. A study measuring mercury across several apex predators in the Atlantic found that swordfish averaged roughly 1,600 nanograms of mercury per gram of wet tissue, with over 80% of that mercury in the methylmercury form. Only shortfin mako sharks had higher average concentrations in that analysis.¹ Stable isotope data from the same study showed that swordfish occupy one of the highest trophic positions among the species tested, which helps explain why they accumulate so much.

Swordfish also have a feeding habit that compounds the problem. Unlike some tunas that mostly hunt near the surface, swordfish regularly dive deep into colder, darker waters to feed on mesopelagic prey, organisms living hundreds of meters below the surface. Mercury isotope research has shown that this deeper foraging exposes swordfish to methylmercury sources that shallow-feeding species do not encounter as heavily.² In short, swordfish pick up mercury both because they are large, long-lived predators and because they hunt in parts of the ocean where methylmercury is particularly available.

What Mercury Actually Does to Your Body

Methylmercury is a neurotoxin. At high enough doses, it damages the nervous system, and the developing brain is far more vulnerable than the adult brain. The most consistent finding across decades of research is that prenatal exposure from maternal fish consumption during pregnancy can cause mild but measurable effects on children’s cognitive development.³ Those effects tend to show up in areas like attention, language, and memory. This is the main reason health agencies single out pregnant women for the strictest fish advisories.

For adults eating swordfish occasionally, the picture is less alarming but still worth understanding. One area of active debate is whether mercury exposure from fish undermines the well-documented heart benefits of eating seafood. Fish is rich in omega-3 fatty acids, which reduce inflammation and appear to protect against heart disease. But some research has suggested that high mercury content in fish may blunt those cardioprotective benefits.⁴ The concern is that you might be getting the omega-3s and the mercury in the same bite, and the mercury partially cancels out the good.

That said, the cardiovascular evidence is not unanimous. A large study published in the New England Journal of Medicine examined mercury levels and heart disease risk in men and found no significant association after controlling for smoking, age, and other risk factors. Comparing men with the highest and lowest mercury levels, the relative risk was essentially flat.⁵ Adjusting for omega-3 intake from fish did not change the result. So the cardiovascular harm from typical mercury exposure remains genuinely uncertain, even as the neurodevelopmental risks during pregnancy are well established.

How Much Swordfish Is Too Much

The U.S. Food and Drug Administration and the Environmental Protection Agency jointly advise that adults who are not pregnant or breastfeeding can eat swordfish, but should limit it to no more than one serving per week. A serving is roughly four ounces of cooked fish, about the size of the palm of your hand. Pregnant and breastfeeding women and children under 12 are advised to avoid swordfish entirely, along with shark, king mackerel, and tilefish from the Gulf of Mexico.

These guidelines are built around the concept of a reference dose: the amount of methylmercury a person can take in daily over a lifetime without appreciable health risk. Because your body eliminates methylmercury slowly, with a half-life of roughly 70 to 80 days, eating high-mercury fish frequently lets levels build up faster than you clear them. A single swordfish steak once a month will not push most healthy adults anywhere near concerning blood mercury levels. The problem arises with regular, repeated consumption, especially if swordfish is your go-to fish multiple times a week.

If you are someone who loves swordfish, the simplest approach is to balance it with lower-mercury options. Salmon, sardines, anchovies, herring, and most shellfish are all rich in omega-3s with far less mercury. Eating those on the weeks you skip swordfish gives you the seafood benefits without the accumulation concern.

Mercury Varies by Where the Fish Was Caught

Not all swordfish carry the same mercury load. Where the fish was caught, how large it was, and the local environmental conditions all contribute to significant variation. A study of swordfish in the western Mediterranean found particularly high mercury levels, which researchers linked to unfavorable feeding conditions and the local food web structure, with cephalopods (squid and their relatives) being a major mercury-laden food source for swordfish in that region.⁶

A broader survey of commercial swordfish from multiple ocean regions, analyzing 220 samples collected between 2014 and 2017 from fish destined for the Italian market, confirmed that mercury levels vary meaningfully across different fishing zones.⁷ Similarly, research comparing swordfish from the Indian and Pacific Oceans found that mercury concentrations in swordfish were roughly comparable between those two regions, though levels of other heavy metals like lead and cadmium differed more sharply.⁸

Bigger swordfish generally contain more mercury than smaller ones, because they have been alive longer and have been accumulating methylmercury for more years. Research across multiple predatory fish species has found significant positive correlations between body weight and mercury concentration.¹ You have no way of knowing from a fillet at the store exactly how large or old the fish was, but this does help explain why mercury readings for swordfish vary so much from sample to sample.

Does Selenium Offer Protection

One piece of the mercury puzzle that gets less attention is selenium, a trace mineral found in many fish. Selenium can bind to mercury in the body, and there is growing scientific interest in whether selenium-rich fish are less dangerous than their raw mercury numbers suggest. The idea is that if a fish has more selenium atoms than mercury atoms (a selenium-to-mercury molar ratio above 1), the selenium may help neutralize some of the mercury’s toxic effects.

Research on selenium-to-mercury ratios in commercial fish has found that people eating large amounts of fish with a ratio below 1, meaning more mercury than selenium, face higher risk from mercury toxicity. As the relative amount of selenium increases, risk appears to drop, though exactly how much excess selenium is needed to meaningfully protect against mercury remains unclear.⁹ Swordfish do contain selenium, but given their very high mercury concentrations, their selenium-to-mercury ratio is not as favorable as it is in lower-mercury species like tuna or salmon. The selenium story is intriguing and may eventually change how risk assessments are done for specific fish species, but for now, regulatory guidelines are still based on total mercury content rather than molar ratios.

Other Contaminants Beyond Mercury

Mercury gets most of the headlines, but swordfish can also contain other heavy metals, particularly lead and cadmium. These enter the ocean from industrial runoff, atmospheric deposition, and natural geological sources. A study of swordfish from Algerian waters found lead levels that exceeded European regulatory thresholds, although mercury in the same fish stayed close to and did not exceed recommended limits.¹⁰ Levels of cadmium, lead, and mercury in swordfish caught from the Indian and Pacific Oceans were found to fall within acceptable levels according to both Indonesian national standards and European Union food safety regulations, though Pacific-caught fish tended to have higher cadmium and lead levels than Indian Ocean fish.⁸

For most consumers eating swordfish occasionally, these other metals are a secondary concern compared to mercury. Lead and cadmium in fish tend to concentrate in organs rather than in the muscle tissue that people typically eat. Still, if you eat swordfish frequently and are already exposed to lead or cadmium from other sources (older plumbing, occupational exposure, smoking), it is worth being aware that fish can be an additional contributor.

Can Cooking Reduce the Risk

How you prepare fish does affect how much mercury your body actually absorbs. Research using laboratory digestion models has found that certain cooking methods reduce the bioaccessibility of mercury, meaning less of the mercury in the cooked fish ends up in a form your gut can absorb. Baking and frying both reduced mercury bioaccessibility compared to raw fish in one study, and co-ingesting garlic or broccoli alongside the fish had a further positive effect on decreasing mercury uptake.¹¹ That study was conducted on a different fish species (pontic shad), so the exact percentages may not map perfectly to swordfish, but the general principle that cooking method and accompanying foods matter likely holds.

Swordfish is most commonly grilled or pan-seared, both of which involve high dry heat. While no study has specifically tested grilled swordfish through the same bioaccessibility analysis, the evidence from baking and frying suggests that cooking at high temperatures helps. Pairing your swordfish with garlic-heavy sauces or cruciferous vegetables like broccoli is, at least in preliminary research, a reasonable strategy that may modestly reduce how much mercury your body takes up from the meal. These are not dramatic reductions that would let you eat swordfish with abandon, but they do suggest that how you prepare the fish is not irrelevant.

The Mislabeling Problem

A concern that most swordfish buyers never think about is whether they are actually getting swordfish at all. DNA barcoding studies from multiple countries have revealed that shark meat is sometimes sold as swordfish, which introduces a different set of safety and ethical issues. In New England fish markets, a barcoding study found a substitution rate of about 10.5%, with samples labeled as swordfish actually identified as mako shark, thresher shark, and other lamnid shark species.¹² Several of those shark species are endangered or threatened.

Similar patterns have turned up elsewhere. In Santiago, Chile, about 8.5% of swordfish samples were fraudulent, with porbeagle shark and shortfin mako being the most common substitutes. Mislabeling rates were highest in small fish markets and open-air markets, while supermarkets showed no fraud in that study. Lower sales prices were a significant predictor of fraud.¹³ Italian researchers have similarly confirmed blue shark, smoothhound, and angular roughshark being sold as swordfish slices.¹⁴

This matters for safety because shark species like mako can carry even more mercury than swordfish. If you think you are eating swordfish once a week and you are actually eating shortfin mako, your mercury exposure could be substantially higher than you planned for. From a conservation standpoint, unwitting shark consumption also drives demand for species that are already in serious decline. Buying from reputable vendors who can trace their supply chain is the most practical way to reduce your chances of being mislabeled, and paying attention to suspiciously low prices is another useful signal.

Environmental Costs of Swordfish Fishing

Safety is not only about what is on your plate. If you care about the environmental footprint of your food, swordfish comes with some baggage. The primary commercial method for catching swordfish is pelagic longlining, where fishing vessels set lines stretching for miles with thousands of baited hooks. This method is effective for catching swordfish but also catches animals it is not targeting, a problem known as bycatch.

Sea turtles are among the most vulnerable bycatch victims in swordfish longline fisheries. A comprehensive meta-analysis covering 41 studies found that replacing traditional J-hooks with circle hooks significantly reduced bycatch of loggerhead, olive ridley, and leatherback turtles, with minimal impact on the catch rates of target species like swordfish and tuna.¹⁵ More experimental approaches are being tested as well. A recent trial using “traplines,” a modified gear type deployed alongside conventional hooks, found that traplines caught only one loggerhead turtle compared to 127 caught by conventional hooks, while still producing a substantial commercial fish harvest.¹⁶

Swordfish populations themselves are in relatively decent shape in some regions, particularly the North Atlantic, where management measures have helped stocks recover after severe overfishing in the 1990s. In the Mediterranean, the picture is less optimistic. Research has documented poor body condition and high mercury levels in western Mediterranean swordfish, raising concerns about the health of that population.⁶ If you are choosing swordfish and want to minimize your environmental impact, looking for fish certified by organizations like the Marine Stewardship Council or sourced from well-managed fisheries is the most practical step available to a consumer.

Parasites and Foodborne Illness

Mercury is a chronic concern, but swordfish, like all fish, also carries acute food safety considerations. Swordfish can harbor parasites, particularly anisakid roundworm larvae, which are common in many marine fish. Cooking swordfish to an internal temperature of at least 145°F (63°C) kills these parasites effectively. Since swordfish is almost always served cooked, this is rarely an issue in practice, unlike with fish commonly eaten raw.

Swordfish can also be involved in scombroid (histamine) poisoning if it is not properly chilled after being caught. When fish with naturally high levels of the amino acid histidine are left at warm temperatures, bacteria convert histidine to histamine, which cooking does not destroy. Symptoms come on quickly after eating, usually within an hour, and include facial flushing, headache, and gastrointestinal distress. The risk is essentially zero if the fish has been kept cold from boat to plate, which is another reason to buy from vendors with good handling practices.

Swordfish Nutrition Beyond the Mercury Concern

It is easy to get so focused on mercury that you forget swordfish is, nutritionally speaking, an impressive food. A four-ounce serving of cooked swordfish provides roughly 20 grams of protein with relatively little saturated fat. It is a meaningful source of selenium (which, as discussed above, may provide some counterweight to its mercury content), vitamin D, and niacin. It also contains omega-3 fatty acids, though in lower concentrations than oily fish like salmon or mackerel.

The protein in swordfish is highly bioavailable, and its dense, meaty texture makes it one of the few fish species that appeals to people who typically avoid seafood. For someone who has been eating no fish at all, even occasional swordfish consumption is likely a net nutritional positive, provided they are not pregnant or in another high-risk category. The goal for most people should not be to eliminate swordfish from their diet but to treat it as an occasional choice rather than a staple, filling the rest of their seafood meals with species that deliver comparable nutrition at a fraction of the mercury.