What is Ono (Wahoo)?
Ono, which means “good to eat” in Hawaiian, is the local name for the fish known globally as wahoo (Acanthocybium solandri). A fast and torpedo-shaped predator, it is a close relative of the king mackerel and is highly prized by sport fishermen and seafood lovers for its firm, white flesh. Ono is found in tropical and subtropical seas worldwide and can grow to over 100 pounds, with an average catch size in Hawaii ranging from 8 to 30 pounds. However, its position at the top of the marine food chain is directly linked to its mercury content.
How Mercury Accumulates in Fish
Mercury enters the marine environment from both natural sources (like volcanoes) and human activities (such as coal combustion). In aquatic systems, bacteria convert this mercury into a highly toxic organic form called methylmercury.
Bioaccumulation and Biomagnification
- Bioaccumulation: Methylmercury is absorbed by marine organisms, and as they consume contaminated water and sediment, it accumulates in their tissues faster than it can be eliminated.
- Biomagnification: This process is magnified up the food chain. Smaller fish with low levels of mercury are eaten by larger fish, which then accumulate even higher concentrations. Since ono is a fast-growing, top-level predator, it has a significant opportunity to accumulate mercury from its diet of smaller fish and squid. Studies on wahoo have found a positive correlation between fish size/age and mercury concentration.
Official Guidelines on Ono Mercury Levels
Health organizations and governmental agencies provide guidance on safe fish consumption based on mercury levels. For example, the Hawaii Department of Health advises that ono be eaten no more than once every two weeks for certain populations, highlighting its place in a higher-mercury category than some other local fish. The FDA and EPA’s broader advice on fish consumption for pregnant women and children includes categories for fish based on their mercury content. Ono falls into the Good Choices category (formerly considered higher risk in older guidelines), though recommendations for specific groups still suggest limiting intake.
Comparing Ono to Other Fish
To put ono's mercury levels into perspective, a comparison with other common seafood items is useful. This helps consumers make informed choices based on their overall diet and health profile. The average mercury concentration for wahoo can be around 0.50 mg/kg, which is significantly lower than high-mercury fish but higher than many low-mercury options.
| Seafood Type | Mercury Level (mg/kg) | FDA/EPA Category | Common Consumption Advice |
|---|---|---|---|
| Swordfish | ~1.0 | Choices to Avoid | Should be avoided by sensitive groups; general population advised limited consumption. |
| Ono (Wahoo) | ~0.50 | Good Choices | Limited consumption, especially for pregnant women and children. |
| Tuna, Bigeye | ~0.689 | Choices to Avoid | Highest mercury tuna; avoid for sensitive groups. |
| Tuna, Canned Light | ~0.012 | Best Choices | Safe for 2–3 servings per week for most. |
| Salmon | ~0.022 | Best Choices | Highly recommended due to low mercury and high omega-3 content. |
| Shrimp | ~0.009 | Best Choices | Very low mercury; safe for frequent consumption. |
Risks and Safe Consumption
While the risk from occasional consumption of ono is low for most healthy adults, risks increase with higher frequency and for sensitive populations. Methylmercury is a powerful neurotoxin that can cause serious health problems with high exposure, including neurological damage and developmental delays in children.
Guidance for Sensitive Groups
- Pregnant and Breastfeeding Women: Because methylmercury can cross the placenta and impact fetal brain development, consumption guidelines are strictest for this group. Ono should be limited to one serving every two weeks, or avoided entirely in favor of lower-mercury options.
- Young Children: Similar to pregnant women, young children are vulnerable to the neurotoxic effects of mercury. Intake should be limited and portion sizes adjusted for body weight.
- General Population: For healthy adults, moderate consumption of ono is generally considered safe. However, eating a variety of fish and avoiding exclusive reliance on higher-mercury species is the best practice.
How to Reduce Your Mercury Exposure from Fish
For those who enjoy seafood but want to minimize mercury intake, there are several simple strategies:
- Choose Smaller Fish: Opt for smaller, shorter-lived species like sardines, anchovies, and Atlantic mackerel, which have less time to accumulate mercury.
- Vary Your Seafood: Instead of eating the same high-mercury fish frequently, rotate your choices. Incorporate low-mercury options like salmon, shrimp, and tilapia.
- Follow Official Guidance: Regularly consult consumption advisories from reputable sources like the FDA and EPA for the latest recommendations on specific fish types. The FDA's advice about eating fish offers a helpful guide for all consumers.
- Consider Sustainable Sources: Look for sustainably sourced ono, which may sometimes come from fisheries that monitor fish size to reduce mercury risk, although this is not a guarantee.
Conclusion
In summary, ono, the Hawaiian name for wahoo, is not a low-mercury fish but rather falls into a moderate-to-high category due to its size and predatory diet. While not as high in mercury as species like swordfish, it requires moderated consumption to be part of a healthy diet, particularly for pregnant women, breastfeeding mothers, and young children. For most healthy adults, enjoying ono in moderation is generally safe. By following official consumption guidelines and prioritizing a diverse intake of seafood, consumers can safely balance the nutritional benefits of fish with concerns about mercury exposure. Making informed choices ensures that the tradition of enjoying delicious ono remains a healthy one.
