Some types of fish have higher levels of a metal called mercury than others. Mercury has been linked to birth defects. To limit your exposure to mercury, follow a few simple guidelines. Choose fish and shellfish such as shrimp, salmon, catfish, and pollock. Do not eat shark, swordfish, king mackerel, or tilefish. Limit white (albacore) tuna to 6 ounces a week. You also should check advisories about fish caught in local waters.