10. Shark

Shark
Since sharks are at the top of the food chain, they have very high levels of mercury [7]. They are also slow to mature and reproduce, and thus overfishing has depleted their populations as well.

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11. Atlantic Bluefin Tuna
Atlantic Bluefin Tuna fish
Bluefin tuna have been severely overfished, and are now considered to be highly vulnerable to extinction [12]. They are also large predatory fish and thus contain high levels of mercury [7].

12. Swordfish
Swordfish
Image Credit: Shimano

Another predatory fish, mercury is the main concern here. In fact, the EDF has recommended that women and children avoid swordfish altogether and men consume it no more than once per month [13].

13. King Mackerel
King Mackerel and Spanish Mackerel fish
Both King Mackerel and Spanish Mackerel have high levels of mercury and should be avoided, especially by women and children [7].

14. Grouper
Grouper fish
Grouper has moderately high mercury levels and is vulnerable to overfishing [7]. It is also often the target for seafood fraud. The “grouper” that is for sale is may actually be a cheaper form of fish that is being mislabeled. One study found that up to 87% of seafood like grouper, cod, and snapper may be mislabeled [14].

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A Note on The Role of Selenium in Mercury Toxicity

Source: WPCouncil.org
If you love fish but you are concerned about mercury toxicity, there is some good news for you- many of the fish that people routinely eat are high in selenium, which may play a role in preventing the absorption of excessive mercury [15]. Still, there is a caveat. This does not mean that you can eat as many high-mercury fish as you want. However, if you do choose to eat some fish that have a higher content of the heavy metal occasionally, co-consuming enough selenium may help to negate negative effects.
The core message here is this: If you’re eating high selenium fish that is low to moderately high in mercury, the overall risk is lower. If you’re consuming fish that is high in mercury but low in selenium (i.e. shark), it’s best to avoid or to consume very rarely.
Fish To Eat More Of
Atlantic mackerel (Scomber scombrus)
This does not mean you have to give up fish altogether, but it highlights the importance of reading labels and knowing where your fish is coming from. Wild-caught Alaskan salmon, Pacific Sardines, and Atlantic mackerel are all high in omega-3s, as well as several other nutrients, and have less of a negative impact on the environment. Other good choices include Albacore tuna that was caught in the US or Canada, Alaska Cod, Arctic Char, Rainbow Trout, among others. The EDF Seafood Selector provides a comprehensive list of the best seafood and fish to eat, including where it should come from and how it should be produced.

The Bottom Line
Variety of seafood
When you’re choosing which foods to eat, it is important not only to consider the impact that those foods will have on your health but also the impact that they’re having on the planet. It is crucial that we as consumers make responsible choices to ensure that our planet- and all the organisms upon it- continue to thrive for future generations.

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Sources
“Omega-3 Fatty Acids.” ODS
“How Does Mercury Get Into Fish?” Scientific American. December 30, 2011.
“Atlantic Cod.” Oceana
“Why 500 Million U.S. Seafood Meals Get Dumped In The Sea.” NPR. Alastair Bland. March 21, 2014.
“Beluga Sturgeon.” Oceana
“Mercury Levels in Commercial Fish and Shellfish (1990-2012).” FDA
“”The American Eel (Anguilla rostrata) – An Under-Appreciated Resident and Important Link to the Health of the Delaware River.” DelawareRiver.
“New Jersey River Polluters Fund Toxic Fish Swap — But There’s A Snag.” NPR. Sarah Gonzalez. January 26, 2016.
“Microbiological and chemical safety concerns regarding frozen fillets obtained from Pangasius sutchi and Nile tilapia exported to European countries.” PubMed. Piotr Kulawik, et al. March 2016.
“Golden King Crab.” Fish Choice
“Orange Roughy.” Oceana
“Atlantic Bluefin Tuna.” Oceana
“SWORDFISH.” Seafood
“Grouper, snapper, cod? Mislabeling is rampant in the seafood industry” CBS News. Oct, 20, 2021.
“Selenium and mercury in pelagic fish in the central north pacific near Hawaii.” PubMed. J John Kaneko , Nicholas V C Ralston. December 2007.
Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.