Because many of the ingredients in sushi are uncooked there is great concern over the safety of eating it. There are additional concerns for pregnant women...
These concerns are very valid - and they should be for many of the foods we eat every day
Concerns can be heavy metal poisoning, toxins (fugu), parasites and shellfish poisoning..
Mercury is a poisonous heavy metal. Small amounts of mercury are present in many foods and generally doesn't become a problem. This becomes a concern because the largest source of mercury entering humans is from fish. Therefore, you should try to limit the amount ingested from them. For fish this means considering the size and age of the fish. Generally small fish such as tilapia or trout will have low levels of mercury. Fish that have higher levels of mercury include shark, swordfish, king mackerel, tilefish and albacore. The EPA and FDA have recommendations for pregnant women limiting the amount of various fish eaten per week.
For fish this means considering the size and age of the fish. Generally small fish such as tilapia or trout will have low levels of mercury.
There are many potential parasites in raw fish. However, you shouldn’t have to worry about them if you are eating fish purchased in America or Europe. These countries require the fish to be frozen either to -4 F (for 168 hrs) or -31° F (for 15 hrs). This can’t be done in a home freezer. Many tuna (Thunnus alalunga, Thunnus albacares (Yellowfin tuna), Thunnus atlanticus, Thunnus maccoyii (Bluefin tuna, Southern), Thunnus obesus (Bigeye tuna), or Thunnus thynnus (Bluefin tuna, Northern) are exceptions to this rule since they are unlikely to have parasites.
If you prepare sushi at home you should buy “sushi grade” fish. Although this term doesn’t have a specific meaning, reputable markets will sell fish that has been inspected and frozen for the appropriate time.
Several microorganisms produce toxins that can travel up the food chain. These toxins can not be removed or neutralized by cooking, smoking, curing, or any other food preparation. For more on this see http://wwwnc.cdc.gov/travel/yellowbook/2014/chapter-2-the-pre-travel-consultation/food-poisoning-from-marine-toxins
Ciguatera is one of these toxins and it occurs mainly in the tropics from reef fish eating dinoflagellates. The prevention consists of eliminating or reducing the intake of fish that are at risk. These include barracuda, moray eel,… Human senses are unable to detect this toxin.
Scombroid fish poisoning results from the improper storage of fish that are normally high in histidines, which break down into histamines. These include tuna, mackerel, mahi mahi, sardine, anchovy, herring, bluefish, amberjack, and marlin.
Shellfish poisoning occurs from eating bivalve molluscs that have consumed specific types of mircoscopic organisms that contains toxins. Bivalves are mollusks that have two shell halves, these include clams, oysters, and mussels. In addition to shellfish poisoning some people are also allergic to shellfish.
There are four types of shellfish poisoning and all occur mainly in shellfish from warmer waters.
One type of shellfish poisoning causes symptoms that you would normally associate with food poisoning. Others may cause tingling, numbness, slurred speach, or even worse. One type can cause a confusion in the senses such as confusing hot and cold, and another can cause memory loss. Two of the types can cause death.
The toxins in the shellfish are not destroyed by cooking. The best way to avoid these toxins, if you are going to eat shellfish, is to buy from reputable sources. Other precautions include noting posted warnings of red tide and don't harvest your own shellfish. In areas where shellfish are harvested the local health department may have additional information. You can also check the web for maps that note closed and safe harvesting areas.