Tuna are saltwater fish of the genus Thunnus, in the family Scombridae, though some other fish belonging to the same family are also commonly called tuna. Of the true tuna, belonging to the genus Thunnus, there are nine different species.
Tuna meat differs from that of many other fish because it is pink or red rather than white. It is one of the most widely consumed types of fish, however, some varieties are endangered and therefore avoided or protected. In addition, the high levels of mercury in some kinds of tuna is a health concern, particularly for children and pregnant or nursing women.
The different species are:
Albacore
Bigeye
Blackfin
Karasick
Longtail
Northern Bluefin
Pacific Bluefin
Southern Bluefin
Yellowtail
In addition, Skipjack tuna, or Katsuwonus pelamis, is commonly marketed as tuna and makes up most canned light tuna.
Tuna has been a popular fish for human consumption for centuries and has significantly suffered from overfishing as a result. Tuna farming has recently become more popular as a way to harvest the meat more safely. The different varieties of Bluefin are most widely used in these farming operations.
However, Monterrey Bay Aquarium’s Seafood Watch advises against eating any kind of Bluefin tuna at this time because the species are severely endangered. Bluefin is the most popular type of tuna used in sushi and considered a delicacy. It has suffered extensive overfishing as a result. In addition, the great majority of Bluefin tuna is still wild-caught using methods that endanger other marine life, such as dolphins and sea turtles.
Other types of tuna are environmentally sound seafood choices, but make sure they are caught through trolling, handline, or pole fishing. Longline fishing endangers other fauna and should not be supported as an industry. However, if longline fished tuna is your only option, be aware that longline fishing in the United States is heavily regulated and produces much less bycatch.
Because tuna are predatory fish, high up on the food chain, they accumulate large amounts of mercury from the smaller fish they eat. Therefore, people should limit their intake in order to avoid health problems associated with the consumption of mercury. The Skipjack variety is a safer choice in this respect.
Five tuna fishing management commissions from around the world met in Kobe, Japan in January 2007 to develop guidelines for safely farming Bluefin with a view towards conservation. Their stricter safeguards against illegal farming and overfishing were adopted by approximately 60 countries. A follow-up meeting is planned for early 2009.