The occasion was a celebration of the state fish, the rockfish. Four chefs demonstrated recipes, and Maryland first lady Kendel Ehrlich was on hand to sample the fish Thursday at an Eastern Shore seafood house.

"Rockfish caught in the Chesapeake Bay are safe and healthy to eat," the state's Department of the Environment declared, using the striped bass's moniker in the Chesapeake.

But amid the celebration, the state released much more sobering news: Striped bass are carrying elevated levels of PCBs, a harmful pollutant. That day, the state told consumers to limit their consumption of the fish, the first time Maryland had issued such a warning for its entire section of the bay.

Maryland officials have said they issued the warnings out of extreme caution, saying rockfish might pose health risks only if eaten frequently over a long period of time.

"Just because you eat the fish doesn't mean anything's going to happen to you," said Joseph Beaman, who heads the ecotoxicology section at the state Department of the Environment.

The warnings issued Thursday said men could eat up to two meals of rockfish a month without increasing their health risks. Children and women of childbearing age were advised to limit consumption of rockfish to one meal a month.

The warnings came after a study that took nearly three years in which 150 rockfish from around the bay were netted and their flesh tested for pollutants.

Virginia has not issued a warning for its part of the bay, though it did warn against striped bass in the Roanoke River in 1998 and against a variety of fish in the state's rivers in 2003.

In particular, the Maryland scientists were looking for mercury -- some of which comes from the exhaust of power plants -- and polychlorinated biphenyls, or PCBs. These were once used to cool electric transformers, though they were banned about 30 years ago. Still, some PCBs remain in the water, and runoff from leaky and broken transformers brings them into the bay, Beaman said.

The PCBs settle on the bottom of the bay and are consumed by small animals, which are in turn consumed by fish and other predators. The chemicals accumulate as they go up the food chain, reaching some of their highest levels in large predators such as catfish, carp and rockfish.

The study found an average of 0.1 parts per million of PCBs in the bay's rockfish, Beaman said. This was about 5 percent of the level seen in more polluted areas such as New York Harbor, Beaman said, but still cause for concern.

In humans, the chemicals have been linked to increased risk of liver cancer in adults and increased risk of developmental problems in children. The change in risk could be as small as one chance in 100,000, Beaman said, but it was still enough to spur the warning.

The Chesapeake Bay Foundation, an environmental nonprofit group, objected to the upbeat tone the state took in announcing the consumption limits.

"We really take exception with the word 'safe,' when you are advising people to eat -- in some cases -- one meal a month,' " said Kim Coble, the foundation's executive director in Maryland. "We would not call that safe."

The news on rockfish was cited yesterday during a news conference at Johns Hopkins University's Bloomberg School of Public Health, where researchers were calling for further study of the bay's effects on human health.

In a case like this, "we realize just how long-lasting our environmental mistakes have been," said Tom Burke, a Hopkins professor who worked on a study of public health and the bay.

It's unclear how the state's warnings will affect seafood vendors and the state's recreational fishing industry. Marion Kaufman, who operates the charter fishing boat JadeLady out of Stevensville, Md., said he had not heard much about it.

"If they're protecting the health of the people, I certainly understand it," Kaufman said. Still, he said, "it will have an effect on the industry, that kind of publicity."

Kaufman said striped bass fishing has been good this year, and his biggest catch was a 45-inch fish this spring.

"It was delicious, absolutely delicious," said Kaufman, who said he doesn't plan to change his habit of eating rockfish two or three times a month.