Source: fda.gov article titled: Questions & Answers from the FDA/EPA Advice about Eating Fish for Women Who Are or Might Become Pregnant, Breastfeeding Mothers, and Young Children
1. What are mercury and methylmercury?
Mercury is an element that occurs naturally in the environment and is also released to the environment through many types of human activity. It can collect in streams, lakes, and oceans, and is turned into methylmercury in the water or sediment. It is this type of mercury that is present in fish. Methylmercury can be harmful to the brain and nervous system if a person is exposed to too much of it over time.
2. Is there methylmercury in all fish?
Nearly all fish contain at least traces of methylmercury. Fish absorb methylmercury from the food they eat. It tends to build up more in some types of fish than others, especially in larger fish that eat other fish and those fish that live longer.
3. Should I not eat fish during pregnancy in order to avoid mercury?
No, fish can contribute to a healthy diet before and during pregnancy and while breastfeeding. Studies with pregnant women have found that the nutritional benefits of fish, like other protein-rich foods, are important for their child’s growth and development during pregnancy and childhood. While it is important to limit mercury in the diets of women who are pregnant and breastfeeding and young children, many types of fish are both nutritious and lower in mercury. Most people eat less than the recommended amount of fish, both in general and during pregnancy. A 2005 FDA Survey found pregnant women typically ate only 2 ounces of fish a week. The chart in this advice shows which fish are the best choices for women who are pregnant, might become pregnant, or are breastfeeding, or for children over 2 years of age. (For advice about feeding children under 2 years of age, you can consult the American Academy for Pediatrics.
4. Can cleaning or preparing (e.g., cooking) my fish reduce the amount of mercury that might be present?
No. Mercury is found throughout the tissue in fish, so cleaning or cooking will not reduce the amount of mercury. The way to reduce the amount of mercury is to eat the fish shown on the chart identified as the “Best Choices.”
5. Should I be concerned if I eat one serving of the fish listed in the “Choices to Avoid” category?
No, but going forward, choose from fish from the “Best Choices” or “Good Choices” categories. Just try to avoid eating the “Choices to Avoid” fish or feeding them to children. We recommend you eat a variety of fish from the “Best Choices” and “Good Choices” categories on the chart.
6. Are there other contaminants in fish?
Yes, however, FDA has found that the levels of other contaminants in commercial fish generally do not raise human health concerns. For many years, FDA has sampled and tested commercial seafood for pesticides and industrial chemicals as well as other heavy metals besides mercury and the results are available on FDA’s website:
Levels of other contaminants vary by location and fish species. State and local health departments or fish and game agencies provide advice on other contaminants, such as polychlorinated biphenyls (PCBs) in fish from particular bodies of water. People who catch their own fish for recreation or as a source of protein in their diets should check for fish advisories for both fresh and marine waters.
It is a good idea to remove skin, fat, and internal organs where other types of harmful pollutants may accumulate for fish you and your friends catch before you cook these fish. This is particularly true because fish from some local waters may be more likely to contain other contaminants.
And remember – eat a variety of fish, not just the same type every time you eat fish. There are plenty of fish shown on the chart to choose from, so there are fish for every taste.
7. Is it true that pregnant women and young children should avoid raw fish?
Yes. The 2015-2020 Dietary Guidelines for Americans and FDA recommend that pregnant women and young children should only eat foods with fish, meat, poultry, or eggs that have been cooked to safe internal temperatures to protect against microbes that might be in those foods. This includes not eating raw fish served as part of sushi or sashimi (Japanese-style foods) that are available in many restaurants and food stores. Pregnant women and young children often have weaker immune systems and are more at risk for foodborne illnesses.