The Concern with Mercury in Seafood
Mercury is a naturally occurring element that is released into the environment through both natural processes and human activities, such as coal-burning power plants. In water, bacteria convert it into a highly toxic form called methylmercury, which is then absorbed by small fish and shellfish. This process is known as biomagnification.
As larger, predatory fish consume smaller ones, the methylmercury accumulates in their tissues, reaching higher concentrations further up the food chain. This is why older, larger, predatory fish like swordfish and king mackerel contain significantly more mercury than smaller, shorter-lived fish like sardines.
While methylmercury poses health risks in high doses, especially to developing nervous systems in unborn babies and young children, most people can safely consume fish as part of a balanced diet. The key is choosing varieties that are known to be low in mercury and following consumption guidelines from health authorities like the FDA and EPA.
What Types of Fish Are Lowest in Mercury?
Selecting smaller, short-lived fish is the most effective strategy for minimizing mercury exposure. The following are widely recognized as being among the safest options, often appearing on the 'Best Choices' lists from health organizations:
- Salmon: Both wild-caught and farmed salmon are generally low in mercury and are excellent sources of omega-3 fatty acids.
- Sardines and Anchovies: These small, oily fish are very low in mercury and packed with beneficial omega-3s, calcium, and vitamin D.
- Tilapia: This mild-flavored freshwater fish consistently ranks low in mercury.
- Cod: A flaky, white fish that is a staple for many and is low in mercury.
- Catfish: Farm-raised catfish has very low mercury levels.
- Pollock: A mild white fish often used in fish sticks and fast-food fish sandwiches, pollock is low in mercury.
- Shrimp and Scallops: Most shellfish, including shrimp and scallops, are very low in mercury.
- Trout: Freshwater trout, like rainbow trout, is a safe and healthy option.
- Crab: Another low-mercury shellfish choice.
- Light Canned Tuna: Canned 'chunk light' tuna, typically made from skipjack, has much lower mercury levels than canned albacore ('white') tuna.
A Comparison of Fish Mercury Levels
To help visualize the difference, the following table compares common fish types based on their average mercury concentration in parts per million (ppm), using data compiled from FDA testing.
| Seafood Type | Average Mercury (ppm) | Category | Notes |
|---|---|---|---|
| Lowest Mercury | |||
| Shrimp | 0.009 | Best Choice | Very low mercury content |
| Scallops | 0.003 | Best Choice | Among the lowest mercury levels |
| Sardines | 0.013 | Best Choice | Small, short-lived fish |
| Salmon | 0.022 | Best Choice | Wild or farmed are low in mercury |
| Tilapia | 0.013 | Best Choice | Reliable low-mercury option |
| Medium Mercury | |||
| Canned Light Tuna | 0.126 | Best Choice | Made from smaller skipjack tuna |
| Cod | 0.111 | Best Choice | Contains higher levels than salmon but still low |
| Canned Albacore Tuna | 0.350 | Good Choice | Higher mercury than light tuna, limit weekly intake |
| Mahi-mahi | 0.178 | Good Choice | Average concentration, one serving per week is advised |
| Highest Mercury | |||
| Swordfish | 0.995 | Avoid | Large, long-lived predatory fish |
| King Mackerel | 0.730 | Avoid | Large predator with high mercury levels |
| Bigeye Tuna | 0.689 | Avoid | Higher mercury than other tuna types |
| Shark | 0.979 | Avoid | At the top of the marine food chain |
| Tilefish (Gulf of Mexico) | 1.123 | Avoid | Highest mercury concentration of common fish |
Making Smart Seafood Choices for All
For the general population, the benefits of eating fish rich in omega-3 fatty acids often outweigh the risks of mercury exposure, provided that safe choices are made. However, certain groups, including pregnant or breastfeeding individuals and young children, are more vulnerable to mercury's neurological effects and should exercise greater caution.
The FDA and EPA provide clear guidance for safe consumption based on these vulnerability factors:
- For the general population: Aim for 2 to 3 servings of fish from the 'Best Choices' list per week, or one serving from the 'Good Choices' list. This ensures a healthy intake of protein and omega-3s without excessive mercury.
- For pregnant or breastfeeding individuals: The recommendation is to consume 8 to 12 ounces of a variety of seafood from the 'Best Choices' list each week. This supports fetal brain and eye development while staying within safe mercury levels.
- For children: Younger children should receive smaller serving sizes, also from the 'Best Choices' list. For example, a 4-ounce serving is recommended for children aged 8 to 10.
Practical Tips for Selecting Low-Mercury Fish
- Choose smaller, younger fish: Since mercury accumulates over a fish's lifetime, smaller, shorter-lived species are consistently lower in mercury.
- Diversify your fish intake: Instead of eating the same type of fish repeatedly, vary your choices from the low-mercury category. This minimizes reliance on any single species and provides a broader range of nutrients.
- Pay attention to tuna labels: Always check if the canned tuna is 'chunk light' (lower mercury) or 'albacore' (higher mercury). Consider canned light tuna as a frequent choice and limit albacore.
- Check local advisories: For fish caught by friends or family in local waters, check regional advisories. Some local freshwater fish may have higher mercury levels due to specific contamination.
- Don't rely on cooking to remove mercury: Mercury is bound to the meat of the fish, so cooking methods like grilling or baking will not reduce its concentration.
Conclusion: Balancing Nutrition and Safety
Fish is a cornerstone of a healthy diet, providing high-quality protein, essential vitamins, and critical omega-3 fatty acids. By understanding what types of fish are lowest in mercury, individuals can confidently include seafood in their meals while minimizing health risks, especially for vulnerable populations. Prioritizing smaller, short-lived species like salmon, sardines, and tilapia, while limiting or avoiding larger predatory fish, ensures that you are safely reaping the nutritional rewards that seafood has to offer. Adhering to guidelines from authoritative sources like the FDA ensures a balanced and safe dietary approach.
For more detailed information and a full list of fish and shellfish, consult the FDA and EPA's official advice on eating fish and shellfish: FDA and EPA Fish Consumption Guidelines.
