But the Food and Drug Administration rejected calls to also put tuna on the do-not-eat list, saying the other four types of fish contain far more mercury than tuna does. Women who had swordfish for dinner last night shouldn't panic, stressed FDA food chief Joseph Levitt. The risk comes from mercury building up, not a single meal. "It is not a one-dose problem. ... They should just simply stop eating it from this time forward," Levitt said. "We want to empower women to protect the health of their unborn child and the best way they can do that here is to avoid eating those four kinds of fish." Fish is widely considered part of a healthy diet; certain types contain high levels of heart-healthy fats. But different types of fish can harbor different amounts of mercury, an element found naturally in the environment and also a pollutant. Pregnant women can safely eat up to 12 ounces of any other cooked fish a week -- from canned tuna to shellfish to smaller ocean fish, the FDA said. Eat a variety, not just one type. Don't eat more than 12 ounces of fish a week on a regular basis and the amount of mercury absorbed won't be worrisome, the FDA said. When ingested in pregnancy, mercury can damage the central nervous system, leaving babies with slower cognitive development. Critics say up to 60,000 children a year may be affected. The FDA deems fish safe if they contain less than 1 part per million of methylmercury, the form that builds up in fish. The larger the fish, the more methylmercury, absorbed both from water and from eating smaller fish. Consumer advocates have pushed the FDA to warn pregnant women about mercury since the early 1990s. "This is a significant potential health risk for the children of pregnant women. But it's easy to avoid," said Caroline Smith DeWaal of the Center for Science in the Public Interest. "FDA has taken an important public health step." But she was surprised the FDA left tuna steaks -- those from large fish, not the canned tuna made from little fish with far, far less mercury -- off the list, and urged the agency to re-examine that advice. If women binge on canned tuna during pregnancy, that could be a problem, too, contends Michael Bender of the Mercury Policy Project. Some states have urged pregnant women to limit canned tuna consumption to 7 ounces a week. The National Fisheries Institute, a seafood industry trade group, questioned if the mercury levels in swordfish and the other species was really high enough to harm, saying it will review FDA records to see whether the warning was justified. FDA's Levitt refused to say how much mercury the agency has found in canned tuna. But he said levels in shark, swordfish, king mackerel and tilefish are three times higher than in fresh tuna. Even critics admit levels in tuna are far, far lower. But what level of mercury the FDA deems safe is under attack. A major scientific report last summer said the agency should follow Environmental Protection Agency safety standards that are four times stricter -- a standard that critics contend do make tuna a concern. The FDA is considering whether to change its standard. "While I am disappointed that the agency has not yet updated their methylmercury action level, this consumer warning is a step in the right direction," said Sen. Patrick Leahy, D-Vt., who had pushed for the warning. While yesterday's warning was aimed at pregnancy, the FDA says it is prudent for nursing mothers and young children not to eat the four mercury-high fish either. The FDA's advise was for commercially caught fish. The Environmental Protection Agency had added advice yesterday for pregnant women who eat fish their family and friends catch: Follow state warnings about fishing from waters with high mercury levels. If your state doesn't issue such mercury warnings, limit locally caught fish to one 6-ounce meal a week as a precaution.