In the first update to a 17-year-old guide on how safe it is to eat fish caught in San Francisco Bay, state health leaders have relaxed some warnings but caution that children and women of childbearing age should not eat perch, white sturgeon, shark or striped bass.

Mercury and PCBs have rendered some of the Bay's most popular sport fish unsafe in any amount for children and woman younger than 45, according to the guidelines.

And perch from San Francisco Bay are unsafe for anyone to eat, the guidelines say.

But for men and women older than 45, the state has found it is significantly safer to eat striped bass than previously thought.

Since 1994, anglers were warned that no one should eat more than two servings of striped bass per month and that striped bass longer than 35 inches should not be eaten.

The new guidelines say men and women older than 45 can safely eat striped bass twice a week.

"Eating fish is good for you, especially fatty fish," said Sam Delson, spokesman for the state Office of Environmental Health Hazard Assessment. "But you need to be careful about contaminants in the fish. It's a balancing act."

The guidelines rely on new information about the concentration of chemicals in fish species collected around the Bay and how those contaminants can affect the health of people who eat them.

In short, the guidelines are for two groups: the first is for children and women to age 45, while the second is for men and women over 45, who are assumed to be past childbearing age.

Children and women of childbearing age also should not eat shark, striped bass or white sturgeon. For this group, the guidelines say it is safe to eat two servings per week of salmon and some other kinds of fish or one serving per week of halibut or white croaker.

For men and women over 45, seven servings per week of salmon or two servings per week of striped bass and other kinds of fish is OK.

Also, the guidelines say it is unsafe to eat any fish or shellfish from the Lauritzen Channel in Richmond's inner harbor because of the very high levels of pesticides found in fish there at the site of a former DDT manufacturer.

State officials plan to print brochures and post signs with the new guidelines, but details, including languages on the signs, have not been worked out.

PCBs are man-made chemicals that can cause cancer. Mercury is a naturally occurring metal that has washed into the Bay mining during the Gold Rush and settles out of the atmosphere from coal-burning in Asia, among other sources. It can cause neurological diseases and can be passed from mother to fetus.

More information about the guidelines is available at http://oehha.ca.gov/fish/nor_cal/2011SFbay.html.