The U.S. Food and Drug Administration has issued new guidelines on eating fish aimed at balancing the risk of mercury exposure with the cardiovascular benefits of seafood.

Under the guidelines, women who are pregnant, nursing or may become pregnant, and young children should not eat certain kinds of fish that tend to be high in mercury. Those fish include shark, swordfish, king mackerel and tilefish.

The guidelines suggest eating up to two meals a week - a total of 12 ounces - of fish known to be low in mercury, such as shrimp, canned light tuna, salmon, pollock and catfish.

The FDA warns that mercury can affect almost any organ in the body. But the agency is most concerned about the potential effect on the brain in young children. At the same time, the agency emphasizes that fish can be a good source of protein and Omega-3 compounds and be an important part of a healthy and balanced diet.

The FDA notes that for people other than pregnant women and young children, fish has many benefits - and there are no specific guidelines on limiting it in the diet.

Health Canada advises consumers limit their consumption of swordfish, shark or fresh and frozen tuna to one meal per week. For young children and women of child-bearing age, the recommended limit for swordfish, shark or fresh and frozen tuna is one meal per month.