Mercury Levels: The Scientific Comparison
When evaluating the safety of seafood, especially for at-risk groups like pregnant women and young children, understanding mercury levels is crucial. The FDA and EPA provide detailed guidance on which fish are low in mercury. Based on extensive testing, it's clear that salmon generally contains lower concentrations of mercury than cod.
Cod's Mercury Profile
Cod is generally considered a lower-mercury fish and falls into the FDA's 'Best Choices' category, allowing for 2-3 servings per week for the general population. However, when compared directly to salmon, its average mercury content is higher. The mean concentration recorded by the FDA is around 0.111 parts per million (ppm). This places cod in a higher-mercury category than salmon but still well below the levels found in high-mercury predators like swordfish and king mackerel. It is important to note that mercury levels in cod can vary depending on factors such as size, age, and specific catch location.
Salmon's Mercury Profile
Salmon is widely recognized as a fish with very low mercury content and is also listed in the FDA's 'Best Choices' category. The average mercury concentration for fresh/frozen salmon is reported to be just 0.022 ppm, making it one of the cleanest seafood options available. The low level of mercury in salmon is primarily due to its position relatively low on the food chain and its shorter lifespan compared to large predatory fish. This is true for most varieties, including wild Alaskan salmon, which often has even lower contaminant levels.
Why Mercury Levels Differ
The difference in mercury accumulation between cod and salmon can be attributed to several biological factors:
- Trophic Level: Mercury bioaccumulates as it moves up the food chain. Larger, longer-lived predatory fish tend to have the highest levels. Salmon are lower on the food chain, feeding on smaller fish and invertebrates. Cod, while not a top predator, consumes a slightly different diet that contributes to higher accumulation over time.
- Lifespan and Size: Older, larger fish have had more time to accumulate mercury. While both species vary in size and age, some varieties of cod may live longer than certain salmon species, allowing for greater mercury buildup.
- Wild vs. Farmed: Farmed salmon typically have lower mercury levels than wild salmon because their diet is more controlled. A 2025 study found that farmed salmon had lower mercury concentrations than wild salmon of similar size.
- Catch Location: The specific waters a fish inhabits can impact its mercury content. Pollution levels vary by region, and fish caught in cleaner, more pristine waters—like those off the coast of Alaska—generally have lower contaminants.
Nutritional Profiles: Cod vs. Salmon
While mercury is a key consideration, both fish offer distinct nutritional benefits. Here is a comparison:
| Feature | Cod | Salmon | Key Difference |
|---|---|---|---|
| Mercury Content | Higher average (e.g., 0.111 ppm) | Lower average (e.g., 0.022 ppm) | Salmon consistently has lower mercury. |
| Omega-3 Fatty Acids | Present, but in lower amounts | Rich source, particularly EPA and DHA | Salmon is a much more potent source of omega-3s. |
| Protein | Excellent source; slightly higher per serving in some cases | Excellent source; generally high quality | Both are great protein sources, but content can vary slightly. |
| Fat Content | Lean, low-calorie option | Higher fat content, contributing to omega-3s | Cod is leaner, while salmon's fat is beneficial omega-3s. |
| Vitamins | Good source of B vitamins, especially B12 | Rich in B vitamins and Vitamin D | Both contain vital vitamins. |
| Flavor Profile | Mild, flaky white fish | Rich, oily, and distinctly flavorful | Personal preference dictates taste. |
Making the Best Choice for Your Health
For most healthy adults, eating a variety of fish, including both cod and salmon, is beneficial and poses minimal risk from mercury. For sensitive populations, such as pregnant or breastfeeding women and young children, following FDA and EPA guidelines is especially important. These guidelines recommend prioritizing fish from the 'Best Choices' list, which includes both cod and salmon, but also advise variety.
To maximize the health benefits while minimizing risk:
- Rotate Your Fish: Don't rely on just one type of fish. Incorporate a variety of low-mercury options, such as sardines, shrimp, and tilapia.
- Favor Wild Salmon: While both farmed and wild salmon are low in mercury, wild-caught Alaskan salmon is often cited as a top, low-contaminant option.
- Check Local Advisories: If consuming fish from local waters, always check for specific advisories, as local pollution can affect mercury levels.
- Prepare Healthfully: Baking, broiling, or grilling fish can reduce overall fat and calorie intake compared to frying.
Conclusion
Ultimately, the answer to the question "Does cod have more mercury than salmon?" is yes, but the distinction is nuanced. Both fish are considered safe and healthy low-mercury options by federal health agencies. However, comparative data shows that salmon contains significantly less mercury than cod on average. While cod is an excellent source of lean protein and vitamins, salmon's higher omega-3 fatty acid content often makes it a more nutrient-dense choice. For a balanced and healthy diet, incorporating both fish, along with other low-mercury seafood, is an excellent strategy.
For the latest official advice on fish consumption, refer to the FDA and EPA's Advice About Eating Fish.
