There is a good website about mercury in fish and shellfish for women who are pregnant, nursing mothers, and children at:
http://www.epa.gov/waterscience/fish/files/MethylmercuryBrochure.pdf.

Also, there is a great website to visit these guidelines in Georgia at:
http://www.georgiaepd.org/Files_PDF/gaenviron/GADNR_FishConsumptionGuidelines_Y2010.pdf.
This tells you the amount of fish safe to eat but not necessarily any ranges.