Read a news story by a San Francisco CBS 5 reporter Barbara Roger.

For someone who watches her diet as much as Wendy Moro, the symptoms didn't add up.

“Severe fatigue and vertigo, very weak. I was at one point able to leg press two hundred pounds, (but) I could barely walk down the block,” says Wendy Moro.

Why, she wondered, would someone who eats so healthily feel so unhealthy? She says doctor after doctor misdiagnosed her condition. Then, Wendy and her current doctor begin to suspect the answer was on her plate.

"A few times a week I was having fish, whether it was once or three times or four times," says Wendy.

"What kind of fish? Swordfish, ahi, tuna and sea bass, the highest mercury-content fish sold in the commercial market," says Dr. Jane Hightower.

Mercury enters the ocean with commercial pollution. It works its way up the food chain, and apparently into to some of the most popular fish on the market. Wendy's doctor, Dr. Jane Hightower, was so suspicious that she began testing dozens of her Bay Area patients. All consumed substantial amounts of fish, and an overwhelming majority tested high for mercury in their systems.

"I was seeing hair loss, fatigue, muscle ache, headache, feeling just an ill feeling." Hightower said.

The symptoms began to clear up when Hightower cut the amount of fish in their diets.

"It was so obvious that this was the problem," she said. "I wanted to rent a tent and a tambourine." (A tambourine is a small one-sided drum with metal disks around its rim).

Her published findings drew national attention. But despite her study, there is still fierce debate over how much fish is safe to eat, and how much mercury consumers are actually ingesting. So we decided to do our own test.

CBS 5 joined with Jane Kay, a reporter for the San Francisco Chronicle. We drove to more than half a dozen high-end fish markets around the Bay Area, and purchased tuna, Alaskan halibut, swordfish, and Chilean sea bass. But instead of the dinner table, our samples wound up packed in ice, and on their way to a testing lab in Washington State.

According to the EPA (Environmental Protection Agency), the safe level of mercury intake for a 120-pound woman like Wendy is a little over 38 micrograms per week. (A microgram is one-millionth of a gram. It is a measurement of weight. One ounce of weight equals more than 28 million micrograms.) Our results? Only halibut was under that limit. On average, a single serving of tuna purchased here in the Bay Area contained more mercury than the EPA recommends a woman of Wendy's size eat for an entire week. Sea bass had nearly twice that level, and swordfish nearly six times the EPA's safe mercury intake for a week, in a single serving.

"When you realized that the problem was on your plate, what did you say?"

"If I had known, I could have prevented so much heartache and illness in my life," said Wendy.

While there is little scientific data on how the body reacts to high levels of mercury, it has been linked to symptoms ranging from muscle pain to hair loss, birth defects, and muscle fatigue. And, as in our testing, the evidence is mounting that the larger the fish, the more the exposure.

"I'm very frustrated," Wendy said. "I feel the government, the FDA (Food and Drug Administration), had this knowledge. This information should have been shared with the public."

"It is a schizophrenic way of thinking to think that we can have a substance that is the second-most toxic element next to plutonium, mercury. We tell people it is so toxic you can't do controlled trials on human subjects with it – yet it's ok to eat it, it won't bother you? What's wrong here? Is anybody listening?" Hightower said.

Note: The Environmental Protection Agency website explains how mercury gets into the fish we eat:

“Mercury occurs naturally in the environment and can also be released into the air through industrial pollution. Mercury falls from the air and can accumulate in streams and oceans and is turned into methylmercury in the water. It is this type of mercury that can be harmful to your unborn baby and young child. Fish absorb the methylmercury as they feed in these waters and so it builds up in them. It builds up more in some types of fish and shellfish than others, depending on what the fish eat, which is why the levels vary.”