In the Northeast, warnings like that are common. Here's Maine's:
"Mercury in Maine freshwater fish may harm the babies of pregnant and nursing mothers, and young children.
Pregnant and nursing women, women who may get pregnant, and children under age 8 SHOULD NOT EAT ANY freshwater fish from Maine’s inland waters. Except for brook trout and landlocked salmon, one meal per month is safe.
All other adults and children older than 8 CAN EAT two freshwater fish meals per month. For brook trout and landlocked salmon, the limit is one meal per week."
New Hampshire's is similar:
"For all freshwater fish, except stocked trout, follow these fish consumption guidelines:
• Pregnant and nursing women, and women who may become pregnant can safely eat ONE, 8-ounce meal of freshwater fish per month.
• Children under age 7 can safely eat ONE, 4-ounce meal of freshwater fish per month.
• All other adults and children age 7 and older can safely eat FOUR, 8-ounce meals of freshwater fish per month.
• When eating bass, pickerel, white perch or yellow perch, limit consumption to fish 12 inches or less in length while following the above guidelines.
Stocked trout contains relatively low levels of mercury. For rainbow and brown trout, women of childbearing age and children can safely eat ONE meal per week; others can eat SIX meals per week. Brook trout could be either stocked or from a native population, and therefore should be consumed at the rate of the general freshwater advisory above."
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