Fish is a good source of protein, and fatty fish like salmon contain high amounts of omega-3 fatty acids. These kinds of fatty acids have been found to have a protective effect against heart disease. The American Heart Association recommends eating fish, particularly fatty fish at least twice a week to reduce risk of developing heart disease. However, some species of fish are high in mercury. Mercury can damage developing fetuses and children. For this reason, women who are pregnant or of childbearing age, and children under 18 should never eat swordfish, golden bass, king mackerel, or shark. They should also limit the amount of albacore tuna and tuna steaks or fillets to no more than 6 ounces per week.