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Fish and Mercury

The levels of mercury found in fresh water fish from Ontario lakes can vary. The Guide to Eating Ontario Fish includes everything you need to know about the safety of eating Ontario sport fish. Check it out online or get a copy from Porcupine Health Unit or the Ministry of the Environment, Conservation and Parks.

Most fish contain trace amounts of mercury. For most people, the small amounts in fish do not pose a problem. Some fish, however, contain high amounts of mercury, which is why certain individuals must be careful about the amounts and type of fish they eat. These groups include:

  • Women of childbearing age;
  • Pregnant women;
  • Nursing mothers; and
  • Children younger than 15 years of age.

How Does Mercury get into fish?

Mercury is released into the air, water, and soil when fossil fuels, such as coal, are burned. It travels long distances with the wind and is deposited in water. It can also be found in the environment naturally.

Once in water, mercury is transformed by bacteria into methylmercury, which is its most toxic form. Methylmercury works its way up the food chain, where it can become concentrated in larger, older fish that eat other fish. It is stored in the muscle of fish, so trimming the fat from fish does not reduce mercury.

What types of fish are safe to eat?

There are many safe and healthy fish to eat. However, some fish have higher levels of mercury. Because mercury affects the developing brain, it’s especially important for women that may become pregnant, are pregnant, or nursing, as well as young children to limit their exposure to mercury in fish.

It is best to choose low mercury fish that is high in omega-3 fats. Examples include:

  • Salmon, anchovy, char, herring, Atlantic mackerel, pollock (Boston bluefish), smelt, rainbow trout, lake whitefish, shrimp, clams, mussels, and oysters.
  • Cod, haddock, halibut, sole, scallops and squid, snapper, perch, bass, and tilapia.
  • Choose “light” tuna. Look for skipjack or tongol on the label. It has less mercury than “white” (albacore) tuna and is generally less expensive.

Anglers using any Ontario lake should consult the interactive Guide to Eating Ontario Fish map online for advisories and track their monthly intake of fish based on the specific advisories for that water body.