The Raw Facts

• The possibility exists that any species of uncooked, fresh fish carries microbes or parasites, so for food safety purposes the U.S. Food Code requires any fish sold for raw consumption to be frozen for a specific period of time to remove that risk. However, certain species of tuna commonly used in sashimi and sushi are fully exempted from that requirement because they are rarely infected.

Safe Species

• Of the more than dozen tuna species, the four commonly found in sushi and sashimi are also legally safe to eat raw. Bluefin is the largest and fattiest tuna; it is a prized delicacy in high demand. Bigeye tuna, or ahi, is a more common fatty species most often used in sashimi and sushi. Yellowfin is also called ahi when served raw, but it is also canned as "light tuna." Albacore, or tombo, is a leaner tuna, served both raw or grilled. Albacore is also canned as "white meat tuna."

Quality Counts

• Whether catching your own tuna or buying a whole fish from a boat or market, choose the freshest, healthiest fish you can find. Look for a tuna with clear eyes, deep red gills and silvery sides. Freshly caught tuna must be stored at 40 degrees Fahrenheit or below, so ask to check the temperature if you are uncertain as to how the fish was kept. Transport your tuna home in ice and store in an ice water slurry in the refrigerator; if the temperature changes it will lose freshness and begins to smell "fishy."

Safety First

• To avoid ingesting harmful bacteria and viruses, doctors generally advise that pregnant women and older adults do not consume raw fish in any form. This is because treating foodborne illness is more difficult in these populations. For food safety purposes, fin fish should be cooked to an internal temperature of 145 degrees Fahrenheit or until the flesh is opaque and flakes with a fork.