Topic Overview

What is mercury?

Mercury is a metal found naturally in the environment. Human activities, such as farming, burning coal, and using mercury in manufacturing, increase the mercury cycling through the air, water, and soil. In water, mercury changes its form and becomes methylmercury. Fish absorb this mercury. When you eat fish containing mercury, you absorb the mercury, and at high levels it can be harmful. Mercury will leave the body over time in the urine, feces, and breast milk.

Do you need to avoid the mercury found in fish?

For most people, the level of mercury absorbed by eating fish and shellfish is not a health concern. Overall, fish and shellfish are healthy foods. They contain high-quality protein and other essential nutrients, are low in saturated fat, and contain omega-3 fatty acids, a type of essential fatty acid. A balanced diet that includes fish and shellfish can contribute to heart health and children's growth and development.

Nearly all fish and shellfish contain traces of mercury. But some contain high levels. Eating large amounts of these fish and shellfish can result in high levels of mercury in the human body. In a fetus or young child, this can damage the brain and nerves (nervous system).

Because of the mercury found in fish, Health Canada recommends that people eat limited amounts of fish high in mercury. Certain people need to limit high mercury fish even more, including:

  • Women who may become pregnant.
  • Pregnant women.
  • Nursing mothers.
  • Young children.

If you are concerned about your or your child's mercury level, talk to your doctor or local health unit about testing.

How should you change your eating habits to reduce your exposure to mercury in fish?

Most people should not eat more than 150 g (5 oz) per week of fish that are known to have higher mercury levels. These include fresh or frozen tuna (not canned "light" tuna), shark, swordfish, marlin, orange roughy, and escolar. Some people need to restrict high-mercury fish even more:footnote 1

  • Nursing mothers or women who are or may become pregnant should limit high mercury fish intake to no more than 150 g (5.3 oz) a month.
  • Children 5 to 11 years of age should limit high mercury fish intake to no more than 125 g (4.4 oz) a month.
  • Children 1 to 4 years of age should limit high mercury fish intake to no more than 75 g (2.7 oz) a month.

Most Canadians don't need to limit how much canned (white) albacore tuna they eat each week. But women who are or may become pregnant, nursing mothers, and children need to limit canned albacore tuna intake to no more than:

  • 300 g (10.6 oz) each week for women who are or may become pregnant, or who are nursing.
  • 150 g (5.3 oz) each week for children 5 to 11 years of age.
  • 75 g (2.7 oz) each week for children 1 to 4 years of age.

Health Canada has no restrictions on eating fish and shellfish that are lower in mercury. These include salmon, rainbow trout, pollock, herring, shrimp, mussels, clams, oysters, and canned "light" tuna.

Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas.

Should a woman who is not planning a pregnancy be concerned?

Mercury accumulates in your bloodstream over time and slowly leaves the body through urine, feces, and breast milk. If you eat a lot of fish high in mercury, it may take up to a year for your mercury levels to drop after you stop eating the fish. If you decide to become pregnant or if you have an unplanned pregnancy, you may have high levels of mercury. While elevated levels of mercury usually do not cause significant health problems, they may affect a developing fetus. If you are of childbearing age, try to follow the guidelines above when you eat fish.

Where can you get more information?

For specific information on your province's or territory's fish consumption advisories, see

For general information on mercury in fish, see:

  • Your local health unit or environmental agency.
  • Health Canada's webpage on mercury at

Related Information



  1. Health Canada (2008). Mercury in fish: Consumption advice: Making informed choices about fish. Available online:


ByHealthwise Staff
Primary Medical Reviewer Sarah Marshall, MD - Family Medicine
Brian D. O'Brien, MD - Internal Medicine
Specialist Medical Reviewer Siobhan M. Dolan, MD, MPH - Reproductive Genetics

Current as ofMay 22, 2015