Fish and shellfish provide protein, are low in saturated fat, are rich in many micronutrients, and provide certain omega-3 fatty acids. However, as a result of natural processes and human activity, fish also contain mercury in the form of methylmercury. Methylmercury can adversely affect the central nervous system, particularly the developing brain of the fetus. As a result, women who are pregnant or may become pregnant, as well as breastfeeding mothers and parents of young children, need information to make informed choices when it comes to fish that are healthy and safe to eat.
In June 2014, the FDA and the U.S. Environmental Protection Agency (EPA) jointly released a draft update to a March 2004 document entitled “What You Need to Know About Mercury in Fish and Shellfish.” The agencies have now announced revised fish advice that contains advice and supplemental questions and answers for those who want to understand the advice in greater detail. The fish advice contains a reference chart that sorts 62 types of fish into three categories:
- Best Choices (36 types of fish)
- Good Choices (19 types of fish)
- Choices to avoid (7 types of fish: King mackerel, Marlin, Orange roughy, Shark, Swordfish, Tilefish (Gulf of Mexico), and Tuna (bigeye))
The reference chart suggests that women of childbearing age (16-49 years old), especially pregnant and breastfeeding women, and parents and caregivers of young children should observe the following guidelines:
- Eat two to three servings of fish a week from the Best Choices list or one serving from the Good Choices list.
- Eat a variety of fish.
- Serve one to two servings of fish a week to children, starting at age two.
- If you eat fish caught by family or friends, check for fish advisories. If there is no advisory, eat only one serving and no other fish that week.
The recommended serving size for an adult is four ounces. For children age four to seven, the recommended serving size is two ounces.
How were fish categorized?
The agencies note that they took a cautious and highly protective approach in determining which fish belonged in each category. They calculated how many servings the average pregnant woman could eat in a week using information on mercury content of each fish type from FDA’s database for commercial fish and other sources. If she could eat that fish at least three times a week, then they listed it in the “Best Choices” category. If she could eat that fish only once a week, or twice but not three times a week, then they listed it in the “Good Choices” category. If she could not eat a serving of that fish once a week, then they listed the fish in the “Choices to Avoid” category.
Why are some fish in more than one category?
The agencies explain why tuna and tilefish appear in multiple categories on the chart. Tuna comes in different types (or species), such as albacore, bigeye, and yellowfin. And because some types of tuna that are bigger or live longer tend to have higher mercury levels, they are in different categories. For example, canned light tuna is in the Best Choices category. Albacore (or white) tuna and yellowfin tuna are in the Good Choices category, and bigeye tuna is in the Choices to Avoid. In addition, fish of the same species that are caught in different geographic locations can vary in mercury content. For example, tilefish are in two categories because tilefish in the Gulf of Mexico have higher mercury levels than those in the Atlantic Ocean. As such, Gulf of Mexico tilefish is in the Choices to Avoid and Atlantic Ocean tilefish is in the Good Choices.
If some species of fish are not on the reference chart, such as mussels, that means the agencies did not have enough reliable mercury data to include it.