Found this! To read more, check out the url
http://www.healthcaresouth.com/pages/askthedoctor/mercuryfish.htm
Women who may become pregnant, pregnant women, nursing mothers, and children 12 years and under can safely eat two meals per week of 6 ounces of cooked, low mercury'' fish: cod, salmon, shrimp, flounder, canned chunk-light tuna, haddock, trout, pollock, squid, shellfish (except lobster) and catfish. Toddlers should eat smaller portions. Fish sticks and fast-food'' sandwiches are commonly made from fish that are low in mercury.
The medium mercury'' fish - striped bass, canned albacore (solid white) tuna, tuna steaks, halibut, lobster, bluefish, grouper - contain three times as much mercury as low mercury fish. One 6-ounce serving can be safely eaten once per week. In the United States, the EPA considers most fish caught in ponds or lakes to be medium mercury.'' However, fresh-water fish in more industrial states, such as Massachusetts, may have higher levels of mercury that may not be safe because lakes tend to be more polluted and concentrated with industrial waste than the ocean. It is best to check either with local officials or check the Massachusetts Department of Public Health web site at
www.state.ma.us/dph/ to determine the safety of local lakes for fish consumption.
The high mercury'' fish - swordfish, shark, mackerel king and tilefish - contain nine times as much mercury as low mercury fish.'' Children and women of childbearing age should not consume these fish.
All other adults can eat these higher mercury fish, in moderation, without health risks. It may be prudent for adults to limit their consumption of higher mercury fish to once per week and eat lower mercury containing fish most times.