Eel is generally a low-to-moderate mercury fish, but the answer depends heavily on whether you’re eating farmed or wild-caught eel. Farmed eel, which is the type served at most sushi restaurants as unagi, averages around 0.21 ppm of total mercury. That puts it well below the 1.0 ppm limit set by regulatory agencies and roughly on par with canned light tuna.
Mercury Levels in Different Types of Eel
Not all eel carries the same mercury load. Farmed Japanese eel (unagi), the variety most commonly found in sushi restaurants and grocery stores, has been measured at a mean total mercury concentration of 0.21 ppm in broiled preparations. The methylmercury fraction, which is the form your body absorbs most readily, averaged just 0.085 ppm. Eel liver, sometimes served as a delicacy, tested even lower at 0.10 ppm total mercury.
Wild-caught eel is a different story. American eels pulled from rivers in Nova Scotia averaged 0.72 ppm of total mercury, with methylmercury at 0.40 ppm. Eels from New Brunswick streams ran even higher, averaging 0.58 ppm of methylmercury. That’s more than three times the methylmercury found in farmed eel, and it pushes wild-caught eel into the moderate-to-high range for mercury.
This gap between farmed and wild eel fits a broader pattern across all seafood. A large synthesis published in Environmental Health Perspectives found that wild-caught fish consistently contained 2 to 12 times more mercury than their farmed counterparts, regardless of species. Farmed fish eat controlled diets and live shorter lives before harvest, both of which limit mercury buildup.
How Eel Compares to Other Fish
To put eel’s mercury in perspective, here’s how it stacks up against fish you probably eat more often, using FDA monitoring data:
- Salmon (fresh/frozen): 0.022 ppm, one of the lowest mercury fish available
- Cod: 0.111 ppm
- Canned light tuna: 0.126 ppm
- Canned albacore tuna: 0.350 ppm
- Fresh yellowfin tuna: 0.354 ppm
- Fresh bigeye tuna: 0.689 ppm
Farmed eel at 0.21 ppm sits between cod and canned albacore tuna. If you’re comfortable eating canned tuna, farmed eel is in a similar range. Wild-caught eel at 0.40 to 0.72 ppm lands closer to fresh tuna steaks, which are typically considered a “limit your servings” fish for pregnant women and young children.
Why Wild Eel Accumulates More Mercury
Eels are bottom-dwelling predators that eat smaller fish, crustaceans, and insects. In the wild, they spend years in rivers and estuaries before migrating to the ocean to spawn. American eels can live 15 to 20 years, and mercury accumulates in muscle tissue over an animal’s entire lifespan. The longer an eel lives and the more contaminated its habitat, the more mercury it stores.
Local water conditions matter enormously. Eels in rivers with industrial runoff or naturally high mercury in sediment will carry more mercury than eels from cleaner waterways. That’s why wild eel mercury readings vary so widely from one study to the next. Farmed eels, by contrast, are typically harvested at a younger age after eating pellet-based diets, which keeps their mercury exposure predictable and low.
Nutritional Benefits Worth Considering
Eel is unusually rich in vitamin A. A single raw fillet contains over 7,000 IU of vitamin A, primarily as retinol, the form your body uses most efficiently. That’s well above what you’d get from most other fish. Eel also provides nearly 2 grams of polyunsaturated fatty acids per fillet, including omega-3s that support heart and brain health.
These nutrients make eel a reasonable part of a varied seafood diet, particularly when you’re choosing the farmed variety. The combination of moderate mercury, high vitamin A, and omega-3 content means the nutritional trade-off favors eating farmed eel in normal amounts. If you’re eating wild-caught eel, especially from rivers where contamination is a concern, keeping portions to once a week or less is a practical approach.
Farmed vs. Wild: What You’re Likely Eating
If you’re ordering unagi at a sushi restaurant or buying packaged eel at an Asian grocery store, it’s almost certainly farmed. The vast majority of commercially available eel, particularly Japanese eel (Anguilla japonica), comes from aquaculture operations in China, Japan, South Korea, and Taiwan. Conger eel (anago), which is also popular in Japanese cuisine, is more commonly wild-caught and tends to carry higher mercury levels as a result.
Recreationally caught eel from North American rivers is the type most likely to have elevated mercury. If you’re catching your own eels, checking local fish consumption advisories is worth the effort. Many state environmental agencies publish species-specific mercury guidance for local waterways, and eel is frequently included because of its tendency to accumulate contaminants over its long life.