Visit the GotMercury calculator posted in a link at the bottom of this thread to calculate your exposure.

Certain fish are more likely to have methylmercury in them than others. Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish. Don't eat Shark, Swordfish, King Mackerel, or Tilefish because they contain high levels of mercury. Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to 6 ounces (one average meal) per week of fish you catch from local waters, but don't consume any other fish during that week.

Of all the fish that you can eat, tuna is the most consumed seafood product, second only to shrimp. Unlike shrimp, it's a significant source of mercury. Nearly all fish and shellfish contain traces of mercury. A good guideline to go by is that which the FDA recommends for pregnant women. The EPA has also set forth guidelines on how much canned tuna is safe to eat, also posted in a table with the NRDC (Natural Resources Defense Council). To protect developing babies from high levels of potentially brain-damaging mercury, the government has warned women who are pregnant, nursing, or even considering having children to eat no more than two to three servings of any fish each week. If you eat tuna, choose light tuna, because albacore ("white") tuna has more mercury than canned light tuna.

Health Canada advises consumers to limit their consumption of swordfish, shark or fresh and frozen tuna to one meal per week; for young children and women of child-bearing age, the recommended limit is one meal per month.

It is difficult to know how much mercury is in any one fish. The level can vary. In America one-in-six children born every year have been exposed to mercury levels so high that they are potentially at risk for learning disabilities and motor skill impairment and short-term memory loss. That type of mercury exposure is caused by eating certain kinds of fish, which contain high levels of the toxin from both natural and man-made sources like emissions from coal-fired power plants. Look around where you live. Begin to notice what type of industry is there. Take walks along the waterways. Look into the industrial history of your area, during the times when waterways were used to carry waste away. Much of the industrial sewage settled into the sediment and remains there. You will have a better understanding of food fish safety when you know the source of your fish. Where does that fish in the supermarket come from?

According to the EPA they recommend the following:

1. Do not eat Shark, Swordfish, King Mackerel, or Tilefish because they contain high levels of mercury.

2. Eat up to 12 ounces (2 average meals) a week of a variety of fish and shellfish that are lower in mercury. Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish. Aalbacore ("white") tuna has more mercury than canned light tuna. So, when choosing your two meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of albacore tuna per week.

3. Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to 6 ounces (one average meal) per week of fish you catch from local waters, but don't consume any other fish during that week.