Is Bonito High in Mercury? Understanding Your Seafood Choices

November 27, 2025 •

4 min read

According to the U.S. Food and Drug Administration (FDA), nearly all fish contain some level of mercury. The key to safe seafood consumption is understanding the differences, which is crucial when asking, "is bonito high in mercury?".

Quick Summary

Bonito generally has lower mercury levels than larger tuna species due to its smaller size and shorter lifespan, making it a safer option for most people. Consumption guidelines still recommend moderation, particularly for vulnerable groups like pregnant women, to manage overall mercury intake.

Key Points

Low to Moderate Mercury: Bonito has lower mercury levels than larger tuna species like bluefin or yellowfin due to its smaller size and shorter lifespan.
Not a High-Mercury Fish: It is generally not categorized as a high-mercury fish, especially compared to larger predators like swordfish.
FDA Guidelines: The FDA often places bonito in a category that is safe for consumption once a week for most people.
Pregnancy Safety: While considered a safer choice than high-mercury fish, moderation is still recommended for pregnant women, nursing mothers, and young children.
Source Matters: The form of bonito, whether fresh, canned, or flakes, can influence its mercury content, with flakes being particularly low.
Moderation is Key: To manage overall mercury exposure, it's best to consume bonito and other seafood in moderation and vary your choices.

Bonito Mercury Levels: A Closer Look

While all fish contain some mercury, the amount varies significantly by species. Bonito is typically considered a low-to-moderate mercury fish, which contrasts with its larger, longer-living tuna cousins, like bluefin and bigeye. This difference is due to several key factors related to its biology and place in the food chain.

The Science Behind Mercury in Fish

Mercury exists naturally in the environment and is also released through industrial processes. In aquatic ecosystems, microorganisms convert this element into methylmercury, a highly toxic form that accumulates in fish tissue. As larger fish consume smaller, mercury-containing fish, the concentration of methylmercury increases up the food chain, a process known as biomagnification.

This process explains why larger, predatory fish at the top of the food chain, such as swordfish and king mackerel, tend to have the highest mercury levels. Bonito's position lower on the food chain, combined with its shorter lifespan and smaller size, means it accumulates less mercury over its lifetime.

Is Bonito High in Mercury? Comparison with Other Tuna

Bonito is often grouped with tuna, which can cause confusion regarding its mercury content. There are many species, and their mercury content varies widely. For example, large predator tuna species like bluefin can have higher mercury concentrations, while skipjack (often labeled as light canned tuna) has relatively low levels.

Bonito vs. Larger Tuna: Bonito is smaller and faster-growing than bluefin, bigeye, or yellowfin tuna, so it accumulates less mercury.
Canned Bonito: Canned bonito, often made from smaller fish, tends to be lower in mercury than canned albacore, which is typically larger. A study in Spain found that canned bonito and tuna had mercury concentrations below permissible levels, though fresh samples sometimes exceeded them.
Bonito Flakes: Used in many Japanese dishes, bonito flakes are made from skipjack tuna and are very low in mercury. The drying and smoking process, however, introduces benzopyrene, though typically in safe quantities.

Recommendations for Consuming Bonito

FDA and EPA Guidelines

The FDA and EPA provide guidance on fish consumption to help consumers make healthy choices. They categorize fish into "Best Choices," "Good Choices," and "Choices to Avoid" based on their mercury content. Bonito often falls into the "Good Choices" category, suggesting it can be consumed once per week by most populations.

Safe Consumption During Pregnancy

For pregnant women, nursing mothers, and young children, who are more vulnerable to the effects of mercury, it is especially important to follow consumption guidelines. Health advisors recommend choosing fish low in mercury while avoiding high-mercury species.

Benefits: Fish provides crucial nutrients like Omega-3 fatty acids, iron, and zinc, which are vital for fetal brain and eye development.
Risks: High mercury exposure can harm a developing baby's nervous system.
Recommendation: While bonito's lower mercury profile makes it a better choice than some other fish, moderation is still advised. Alternating with other low-mercury options is a safe strategy.

Comparison Table: Mercury in Common Fish Species


Fish Species	Typical Mercury Level	Safety Ranking	Notes
Bonito	Low to Moderate	Good Choice	Smaller size and shorter lifespan lead to lower mercury accumulation.
Skipjack Tuna	Low	Best Choice	Often used for canned "light" tuna; low mercury makes it very safe.
Albacore Tuna (Canned)	Moderate	Good Choice	Typically higher in mercury than skipjack due to larger size.
Yellowfin Tuna	Moderate to High	Good Choice	Larger than bonito, thus higher mercury; should be limited.
Bluefin Tuna	High	Choice to Avoid	A large predator with very high mercury levels.
Salmon	Low	Best Choice	Excellent source of Omega-3s with low mercury.
Swordfish	High	Choice to Avoid	A large predator at the top of the food chain.

Sustainable and Fresh Bonito Sourcing

As with any seafood, the source and handling of bonito can affect its quality and safety. Choosing responsibly sourced bonito not only supports sustainable fishing practices but also ensures a fresher, healthier product. For optimal safety, fresh bonito should be handled and stored properly to avoid issues like histamine accumulation. Seeking bonito caught by hook and line can often indicate more sustainable practices.

Conclusion: Making Informed Choices

So, is bonito high in mercury? The answer is no, not when compared to larger, longer-living predatory fish like swordfish or some large tuna species. As a smaller member of the tuna family, bonito's mercury levels are relatively low, making it a viable and nutritious part of a balanced diet. However, as with all seafood, moderation is key, especially for sensitive populations such as pregnant women. By following consumption guidelines and varying your protein sources, you can safely enjoy the benefits of this delicious fish.

Remember to consider the source, whether fresh, canned, or dried flakes, and consult health guidelines for your specific needs to make the best decision for your health.

Frequently Asked Questions

No, bonito is not considered high in mercury. Due to its smaller size and shorter lifespan compared to larger, longer-living tuna species, its mercury accumulation is relatively low.

Bonito has lower mercury levels than larger tuna species like bluefin and bigeye. It's often comparable to skipjack tuna, which is used for canned 'light' tuna, and is a safer choice than albacore tuna, which has higher mercury content.

Yes, bonito is considered one of the safer options for pregnant women due to its lower mercury content compared to many other fish. However, health experts still advise consuming it in moderation and varying your fish choices.

No, bonito flakes are very low in mercury. They are made from skipjack tuna, which is a small, fast-growing fish with minimal mercury accumulation.

Bonito is a species of fish in the Scombridae family, which also includes tunas and mackerels. It is a fast-swimming, migratory fish, smaller than most true tuna species.

High mercury exposure, particularly methylmercury, can cause neurological damage and harm the nervous system, kidneys, and cardiovascular health. It is especially dangerous for a developing fetus and young children.

You can reduce your mercury intake by consuming fish in moderation, choosing smaller, younger fish, and prioritizing species known to have low mercury levels, such as salmon, shrimp, and sardines.