Pregnant women can eat up to 12 ounces per week  of cooked Fish and Seafood from this table.
Tuna (canned. light)       
Perch Ocean
Cod
Carp
Lobster Northern (American)
Herring
Trout Freshwater
Crab  (Blue, King, and Snow)
Haddock (Atlantic)
Crawfish
Pollock
Catfish
Squid
Salmon (Fresh or frozen)
Anchovies
Tilapia
Oysters
Clam
Shrimp
Salmon (Canned)
Scallop
In order from highest to lowest mercury level with tuna having the
highest level of mercury.
http://www.obfocus.com/nutrition/Seafood.htm