But both government agencies continue to stress that many seafoods are low in mercury and that fish is a healthy food and is a good source of protein and other nutrients. The trade association the National Fisheries Institute also cited the health benefits of fish. The organization expressed concern that the guidelines might alarm consumers and cause them to avoid fish.

"The concern is that there could be a mental effect on a young child," said Lester Crawford, deputy commissioner of the Food and Drug Administration. While mercury can affect many organs, the brain is the most sensitive, he said.

FDA said certain fish — notably shark, swordfish, king mackerel, and albacore tuna — contain higher levels of mercury and should be avoided by small children and women who are pregnant, likely to become pregnant or are breast feeding. Shrimp, canned light tuna, salmon, pollock and catfish are safer, the agency said.

Hawai'i officials looked at mercury data and last year sought and received an exemption that allowed it to replace tuna with salmon in a program for breast-feeding women in low-income families.

"We made a request to let our clients elect canned salmon instead of canned tuna. Hawai'i was the first state to get that granted," said Sue Uyehara, program support section chief for the state Department of Health Women Special Supplemental Nutrition Program for Women, Infants and Children (WIC).

The program also created a brochure, "A Local Guide to Eating Fish Safely," which is available on the Department of Health web site, at www.state.hi.us/doh/publichealth/fishsafety.pdf.

The brochure notes that fish that are higher on the food chain can have higher levels of mercury, since the compound bioaccumulates — small fish absorb it from the water, while predators build up in their tissues the mercury from all the smaller fish they eat.

"This is an important story. Good for the FDA for finally making these guidelines," said Sher Pollack, WIC quality assurance coordinator.

The Health Department breaks fish into three categories based on likely mercury levels.

Its recommendations: Top predators like 'ahi, ono and opah should be eaten no more than once every two weeks; the second level, fish to be eaten no more than weekly, include aku (skipjack tuna), mahimahi, canned tuna, nairagi (striped marlin), cod, grouper, orange roughy, pollock and halibut; Akule, awa, moi, mullet, salmon, ika (squid), tako (octopus), scallops and shrimp can generally be eaten any time.

Prominent Hawai'i physician Dr. Terry Shintani recommends fish be eaten far less than that. Shintani is the author of "Hawai'i Diet" and "The Good Carbohydrate Revolution."

"Optimally, most people should eat fish rarely. That doesn’t mean people should eat more chicken and meat. They are no more free of contaminants — just different.

"To me, a plant-based diet is the healthiest. These contaminants don’t bioaccumulate in plants," Shintani said.

The consumption of fish has been promoted in recent years because the food contains omega-3 fatty acids that can be good for the heart. The American Heart Association recommends eating fish at least twice weekly, and more often if you are diagnosed with heart disease.

The response of the FDA and the Environmental Protection Agency, which joined it in making fish-consumption recommendations, follows that of the Hawai'i Department of Health in emphasizing fish lowest in mercury. The federal guidelines suggest that two meals weekly of a low-mercury fish is appropriate, with the weekly fish intake totalling 12 ounces.

"By following these guidelines, we’re confident that women and young children can safely include fish as an important part of a healthy diet," Crawford said.