The idea of getting sushi or sashimi fresh from the ocean may sound like a good thing, but this isn't always the case. Tuna, however, is one fish that is relatively safe to eat raw without freezing it first, but not without a small risk to your safety. To minimize this risk, take care when preparing and serving tuna, and don't eat raw tuna every day.
Many types of fish contain parasites that can make you sick if you eat the fish raw from the ocean. The U.S. Food and Drug Administration requires that fish meant to be eaten raw be frozen at a temperature of -4 degrees Fahrenheit or below for at least 168 hours, or one week. Freezing gets rid of most, but not all, of these parasites, so there is still some risk. Tuna is one of the exceptions to this rule, because it doesn't usually contain these parasites. It can still be contaminated with bacteria or other organisms, however, especially if you don't take care to keep raw tuna away from other types of raw meat or fish, or if you don't store and prepare it properly.
Unfortunately, fresh tuna can be high in mercury, in part because they are large fish near the top of the food chain. Types of raw seafood that are lower in mercury include salmon, eel, abalone, shrimp, clam, scallops, squid, crab, trout, sea bream and octopus. Choose these types more often when eating sushi or sashimi. Big eye and ahi tuna are highest in mercury. Yellowfin tuna is a bit lower in mercury, and skipjack tuna is the lowest-mercury choice among fresh tuna. Canned white tuna is similar in mercury content to yellowfin tuna, and canned chunk light tuna is the type of tuna lowest in mercury.
If purchasing tuna to be eaten raw, make sure that it is sushi grade. Check that the store you buy it from keeps it separate from non-sushi grade fish, and that seafood handlers use separate gloves, cutting boards and knives for sushi-grade fish. Keep the fish frozen or refrigerated until you are ready to use it, and don't leave it out of the refrigerator for more than two hours. Use clean cutting boards and utensils to prepare raw tuna, and wash your hands before and after preparing the fish.
Who Should Avoid Raw Tuna
Pregnant women and people with weakened immune systems should avoid eating any raw fish, including tuna. The American Pregnancy Association recommends that pregnant women avoid big eye and ahi tuna. It also recommends that pregnant women eat no more than three 6-ounce servings per month of canned white tuna or yellowfin tuna, and no more than six 6-ounce servings per month of skipjack tuna or canned light tuna. The mercury in tuna can cause problems with the unborn child, and the potential contamination with organisms that cause foodborne illnesses could also be dangerous. Cooking kills many of these organisms. Children also should avoid eating fresh tuna because of its high mercury content, but can safely eat up to 12 ounces of lower-mercury fish, such as canned light tuna, or 6 ounces of canned white tuna per week, according to the U.S. Food and Drug Administration.
- The New York Times: Sushi Fresh From the Deep . . . the Deep Freeze
- PBS.org: The Myth of Sushi-Grade
- Natural Resources Defense Council: Guide to Mercury in Sushi
- U.S. Food and Drug Administration: Fresh and Frozen Seafood: Selecting and Serving it Safely
- American Pregnancy Association: Mercury Levels in Fish
- Consumer Reports: How Much Tuna Is Safe?