Below is really good video from the FDA about basic seafood safety.
The big deal over pregnancy and fish is generally mercury content. Issues with sushi come from bacterial concerns and food safety concerns. I know I ate fish at least once a week for the 30 some odd weeks I was pregnant and yes, I ate sushi - homemade. Yellowfin tuna is my absolute favorite and I remember when I was 27 weeks pregnant and my husband brought home over 30 lbs of the stuff , lets just say there was no holding me back. I feel like eating sushi while pregnant is a personal choice, I felt comfortable enough to eat fish that I knew was properly handled by my husband but I didn't hit up the grocery store counter. Not for lack of love for my Harris Teeter sushi chef, that was just my comfort zone.
A quick word on shell fish. Shell fish is very good for you despite rumored cholesterol issues. Treat shellfish the way you would anytime make sure that your shell fish is live (exception shrimp and scollops), stored properly, washed properly and cooked thoroughly.
|The Husband's Haul - Triggerfish and Bee Liners (snappers)|
Mercury is altogether a different issue. High mercury in a fish can correlate age, size, and diet of the fish. Mercury is a heavy metal that is retained in muscle tissue (the parts we eat). This in turn allows the mercury levels of our bodies to increase upon consumption because we retain it too (I'll spare you molecular breakdown timelines here). The longer a fish lives the more chance it has of containing high mercury levels in it's tissues. For example, a dolphin (mahi mahi) lives 4 year - MAX - I can count the number of 4 year old dolphin I've seen on one hand (I've aged hundreds of them) - very fast growth (as much as 1.43 mm per day) combined with a short life equates to a nearly zero chance of mercury. King mackerel on the other hand can live to be in there upper 20s - a large king mackerel will be anywhere from 21 to 27 years old. So a large, old fish is likely to contain much higher amounts of mercury. The diet of the species of fish does play a role as well and where the diet comes from. I don't want any information here to keep you from eating any type of fish. As with anything moderation is key, I love swordfish tacos, but I don't eat a pound of swordfish every day - that is where you run into problems.
|Cross section of an otolith under a microscope. This is a 6 year old trout.|
Fun Fact: The oldest fish I've ever aged was a black drum, it was 67 years old.
Common fish most likely to contain low amounts of mercury include: mahi mahi (dolphin), wahoo, trout, flounder
Common fish most likely to contain higher amounts of mercury include: tilefish, king mackerel, large groupers, swordfish, and sharks
Some fish walk the line - tuna, triggerfish, seabass
If this raises additional questions for you - let me know! I love getting to answer questions like this. I feel strongly that seafood is an all to important part of our diets that is often neglected and over looked.