M.L.
Commercially caught fish from safe environments have better controlled environments so you can eat closer to 12 oz a week.
Salmon, talapia, crab, shrimp, lobster, sea bass, sole, flounder, haddock, halibut, ocean perch, cod, canned tune (safer than fresh), farm raised trout, small ocean fish, farm raised fish, canned fish and seafood all are okay if well cooked and in moderation are all safe in moderation (approx 12 oz a week).
6 ozs of cooked fresh freshwater fish caught by family and friends is generally okay (as the contamination content of the water is not known).
Avoid fish from contaminated waters (industrial runoff, sewage leakage) or countries with less than standard cleanliness guidelines, and avoid tropical fish like, grouper, mahimahi and amberjack.
According to the EPA guidelines for pregnant and nursing women, ones to absolutely stay away from is sushi (raw) due to possible contamination and larger ocean fish such as swordfish, king mackeral, tilefish and shark due to high levels of methyl mercury.
Shell fish have lots of bacteria, so make sure they are prepared very carefully and cooked well and they too should be okay in moderation.
Smoked fish have preservatives, so those are good to stay away from.
All of this info came from my "what to expect while you're expecting" book by pregnancy experts.