Are sardines or tuna higher in mercury?

December 11, 2025 •

3 min read

According to the FDA, sardines have a mean mercury concentration of 0.013 parts per million (ppm). This is notably less than the 0.12 ppm found in canned light tuna and the 0.35 ppm in albacore tuna. This difference is why many health experts recommend sardines over tuna for those concerned about mercury exposure.

Quick Summary

Sardines contain significantly less mercury than tuna. The smaller size of sardines and their position lower on the food chain, or biomagnification, is a major factor. This makes sardines a safer and nutrient-dense choice, particularly for frequent consumption.

Key Points

Sardines Have Less Mercury: Due to their smaller size and shorter lifespan, sardines have a significantly lower mercury concentration than tuna.
Tuna Varies by Type: Mercury levels in tuna differ; canned light tuna is lower than albacore, while bigeye tuna has the highest concentration.
Biomagnification is the Cause: Mercury accumulates up the food chain, causing larger predatory fish like tuna to have higher levels than smaller fish like sardines.
Official Guidelines: The FDA classifies sardines as a 'Best Choice' for consumption, while albacore tuna is a 'Good Choice' with more limited recommendations.
Sardines are Nutrient Powerhouses: Sardines offer more omega-3s, calcium (from bones), and vitamin D compared to canned tuna.
Healthier for Frequent Consumption: For those who eat fish regularly, choosing sardines over tuna is a safer option to minimize overall mercury exposure.

Understanding Mercury in Fish

Mercury is a naturally occurring element, released into the environment through industrial pollution and natural processes. In aquatic environments, bacteria convert elemental mercury into a toxic organic form called methylmercury. Fish and other aquatic life then absorb this methylmercury from the water as they feed.

The Process of Biomagnification

Biomagnification explains why mercury levels differ between fish species. It is the process by which methylmercury accumulates in the tissues of organisms at higher trophic levels (higher up the food chain). Small fish consume mercury-laden algae and plankton. Larger, predatory fish eat many of these smaller fish, causing the mercury to accumulate and concentrate in their bodies over time. Therefore, a large, long-lived predator like tuna has much higher mercury levels than a small, short-lived fish like a sardine.

Sardines vs. Tuna: A Detailed Comparison

Consider data from health agencies to highlight the difference in mercury content. The FDA classifies fish based on mercury levels, recommending different consumption frequencies, especially for vulnerable populations such as pregnant women and young children.

Official Mercury Levels

Sardines: The FDA classifies sardines in the 'Best Choice' category due to their very low mercury levels. With a mean concentration of just 0.013 parts per million (ppm), sardines are one of the safest seafood options.
Canned Light Tuna: Also a 'Best Choice', canned light tuna has a higher mean mercury concentration of 0.12 ppm, primarily consisting of the smaller skipjack or tongol species.
Albacore ('White') Tuna: Classified as a 'Good Choice' due to its higher mercury content, with a mean of 0.35 ppm. Consumption is recommended in more limited quantities than canned light tuna.
Bigeye Tuna: This large predator has among the highest mercury levels and is on the 'Choices to Avoid' list for vulnerable groups.

Nutritional Comparison Table


Feature	Sardines	Canned Light Tuna	Albacore Tuna
Mercury Level (Mean PPM)	0.013 (Very Low)	0.12 (Low)	0.35 (Medium-High)
Omega-3 Fatty Acids	Very High	Good Source	High
Calcium	Very High (from bones)	Low	Low
Vitamin D	Very High	Good Source	High
Protein	High	Very High	Very High
Fat Content	Higher (oily fish)	Very Low (leaner)	Low
Sustainability	Generally good	Depends on species and fishing method	May be less sustainable

The Health and Safety Verdict

A complete picture of health benefits and risks is essential for informed dietary choices. For individuals concerned about mercury exposure, the difference between sardines and tuna is crucial.

Sardine Advantages

Extremely Low Mercury: The safest option for regular consumption due to the low risk of mercury buildup.
Rich in Calcium and Vitamin D: A 3-ounce serving of canned sardines with bones provides over 35% of the Daily Value for calcium.
Excellent Omega-3 Source: Contain higher combined levels of DHA and EPA compared to canned tuna.
Sustainable: Generally a more sustainable seafood choice because sardines are small and reproduce quickly.

Tuna Considerations

Varies by Type: Not all tuna is the same. Canned light tuna is much lower in mercury than albacore and bigeye tuna, making it a more prudent choice.
Lean Protein Source: An excellent source of lean, high-quality protein, especially varieties packed in water.
Consumption Limits: Regulatory bodies advise limiting higher-mercury types. For example, Harvard Health suggests limiting albacore tuna to no more than 6 ounces per week for adults.

Making the Right Choice for You

Sardines are a clearly superior option for managing mercury intake for individuals with a high dietary intake of fish or those in vulnerable populations. They offer strong nutritional benefits with minimal risk. For others, canned light tuna can be safely included in moderation as part of a varied seafood diet.

For additional information and official guidelines on mercury in seafood, refer to the FDA's Advice About Eating Fish.

Conclusion

In comparing sardines and tuna, tuna is unequivocally higher in mercury. Sardines, as smaller prey fish, accumulate less mercury than their larger, predatory counterparts due to biomagnification. Sardines are the safer, lower-mercury choice, particularly for those who eat canned fish frequently, though both offer nutritional benefits like lean protein and omega-3 fatty acids. Understanding these differences allows for informed decisions to enjoy the health benefits of seafood while minimizing potential risks.

Frequently Asked Questions

Sardines are smaller, shorter-lived fish that feed on plankton, placing them low on the food chain. Tuna are larger predators that eat other fish, causing mercury to accumulate and concentrate in their bodies through a process called biomagnification.

Yes, canned tuna is generally safe in moderation. Canned 'light' tuna (mostly skipjack) is a 'Best Choice' according to the FDA. Canned albacore ('white') tuna has higher mercury and should be limited, especially for vulnerable populations like pregnant women.

Yes, sardines are on the FDA's 'Best Choice' list and are a great option for pregnant women due to their low mercury levels and high omega-3 fatty acid content, which is important for fetal brain and eye development.

Not necessarily. The type of tuna matters more than whether it's fresh or canned. Canned light tuna (skipjack) is lower in mercury than most fresh tuna steaks (which are often larger species like albacore or yellowfin).

Sardines are a much better source of calcium. When canned, they are typically eaten with their edible, softened bones, which provide a substantial amount of calcium.

Because of their very low mercury levels, sardines can be enjoyed frequently as part of a healthy diet. Health organizations often recommend two to three servings of low-mercury fish per week for the general population.

No, draining the liquid from canned fish does not reduce the mercury content. Mercury is primarily contained within the fish's flesh, not the canning liquid.