Mercury is a naturally occurring element that finds its way into waterways from both natural sources and industrial pollution. Once in the water, microorganisms convert it into methylmercury, a highly toxic organic form that is easily absorbed by aquatic organisms. This process of bioaccumulation means that mercury builds up in species higher up the food chain. Larger, long-lived predatory fish accumulate the highest concentrations as they consume smaller fish that also contain mercury. For this reason, the biggest fish are often the highest risk for mercury contamination.
Fish with the highest mercury content
Federal agencies like the U.S. Food and Drug Administration (FDA) and Environmental Protection Agency (EPA) provide guidance on fish consumption based on mercury levels. The following species are generally considered to have the highest levels and should be limited or avoided, especially by vulnerable groups like pregnant or nursing women and young children:
- Shark: A large, predatory fish at the top of the food chain.
- Swordfish: Another large, long-lived predator with very high mercury levels.
- King Mackerel: Specifically the larger species, not the smaller Atlantic mackerel.
- Marlin: Similar to swordfish, a large ocean fish that can have elevated mercury.
- Orange Roughy: A long-living, slow-maturing deep-sea fish.
- Bigeye Tuna: This specific type of tuna contains significantly more mercury than canned light tuna.
- Tilefish (Gulf of Mexico): This region's tilefish consistently shows the highest mercury levels.
Medium and low mercury fish choices
Moderation is key when selecting seafood. Some fish have medium levels of mercury, meaning their consumption should be limited, while others are low in mercury and can be safely consumed in greater quantities.
Comparison of Mercury Levels in Fish
| Mercury Level | Example Species | Consumption Guidance (for general population) |
|---|---|---|
| High | Shark, Swordfish, King Mackerel, Bigeye Tuna, Orange Roughy, Marlin | Avoid or limit consumption significantly. |
| Medium | Albacore Tuna (canned), Halibut, Mahi Mahi, Grouper, Snapper | Up to one serving per week. |
| Low | Salmon, Shrimp, Sardines, Canned Light Tuna, Catfish, Tilapia, Cod | Two to three servings per week. |
Low-mercury seafood options
For those seeking nutrient-rich seafood with minimal mercury risk, there are many excellent options. These species are generally smaller and lower on the food chain, resulting in less bioaccumulation.
- Salmon (fresh or canned)
- Shrimp
- Canned Light Tuna (skipjack variety)
- Sardines
- Anchovies
- Cod
- Tilapia
- Catfish
- Scallops
Risks for vulnerable populations and how to manage intake
Developing fetuses and young children are most vulnerable to the neurotoxic effects of methylmercury exposure. For this reason, federal health agencies issue specific recommendations for pregnant or nursing women and children. A pregnant woman's mercury levels can take over a year to decrease, so it is important for women planning a pregnancy to also be mindful of their fish consumption.
Managing your mercury intake involves making informed decisions about the type and amount of fish you eat. Following guidelines from authoritative sources like the FDA and EPA is the best course of action. When purchasing fish, consider its origin and species. For instance, canned light tuna is a safer choice than albacore tuna, and smaller, younger fish are generally lower in mercury than large predators. For locally caught fish, checking local advisories is critical, as mercury levels can vary by specific waterway. Simply by diversifying your seafood choices and opting for lower-mercury options, you can enjoy the many nutritional benefits of fish while minimizing your exposure risk.
Conclusion
While many fish offer significant health benefits, certain species contain high levels of mercury that pose health risks, particularly to vulnerable populations. By prioritizing smaller, low-mercury fish like salmon and shrimp and limiting the consumption of large predators such as shark and swordfish, you can effectively manage your mercury intake. Educating yourself on the different mercury levels in seafood is a simple yet powerful step toward a safer and healthier diet.
Understanding the latest FDA/EPA guidance is crucial for making safe seafood choices.
