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Tuna

Tuna

Tuna are salt water fish from the family , mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of 70 km/h (43 mph). Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an oxygen-binding molecule, which tuna express in quantities far higher than most other fish. Some larger tuna species, such as bluefin tuna, display some warm-blooded adaptations, and can raise their body temperatures above water temperatures by means of muscular activity. This enables them to survive in cooler waters and to inhabit a wider range of ocean environments than other types of fish.

Tuna History and Tuna Facts

Only about one percent of tuna comes to the market to be sold fresh. The rest goes to the cannery, because canned tuna is America's most popular fish. If you haven't yet tried fresh tuna, you're missing one of the best meals to come from the ocean.

Tuna History

The word tuna dates back only to 1880 in print and is attributed as a Spanish American derivation of the English counterpart, tunny. It is derived from the Latin Thunnus, the name of its scientific genus. Tuna has been fished from the warm, temperate parts of the Mediterranean Sea and the Pacific, Atlantic, and Indian Oceans since ancient times. As a member of the mackeral family, tuna naturally has a stronger, more robust flavor than whitefish.

Tuna Facts

Tuna can cruise up to 55 miles per hour, and they are constantly in motion. To keep this speed machine going, the tuna eats up to ten percent of its body weight daily. Depending on the variety, weights average from 10 pounds up to 600 pounds per fish. The majority of the commercial tuna harvest comes from California. The average consumption of tuna in America is 3.6 pounds per person, per year, most of which is canned.

 

Etymology

"Tuna" comes from the Spanish word atún, from Arabic تن or تون tun/tūn, from Latin thunnus, from Greek θύννος, thynnos.

Taxonomy

Bar chart that states Thunnus thynnus is the largest tuna, at 458 centimetres (180 in) followed by Thunnus orientalis at 300 centimetres (120 in), Thunnus obsesus at 250 centimetres (98 in), Gymnosarda unicolor at 248 centimetres (98 in), Thunnus maccoyii at 245 centimetres (96 in), Thunnus albacares at 239 centimetres (94 in), Gasterochisma melampus at 164 centimetres (65 in), Thunnus tonggol at 145 centimetres (57 in), Thunnus alalunga at 140 centimetres (55 in), Euthynnus alletteratus at 122 centimetres (48 in), Kanbcznmbazdmnbdfmbdmnmn.jgnbtsuwonus pelamis at 108 centimetres (43 in), Thunnus atlanticus at 108 centimetres (43 in), Allothunnus fallai at 105 centimetres (41 in), Euthynnus affinis at 100 centimetres (39 in), Auxis thazard thazard at 65 centimetres (26 in),Auxis rochei rochei at 50 centimetres (20 in), and Auxis rochei eudorax  at 36.5 centimetres (14.4 in)
Maximum reported sizes of tuna species

There are over 48 different tuna species. The Thunnus genus includes 9 species:

Species of several other genera (all in the family Scombridae) have common names containing "tuna":

Biology

A remarkable aspect of Thunnus physiology is its ability to maintain body temperature above that of the ambient seawater. For example, bluefin can maintain a core body temperature of 75–95 °F (24–35 °C), in water as cold as 43 °F (6 °C). However, unlike typical endothermic creatures such as mammals and birds, tuna do not maintain temperature within a relatively narrow range.[1]

Tuna achieve endothermy by conserving the heat generated through normal metabolism. The rete mirabile ("wonderful net"), the intertwining of veins and arteries in the body's periphery, transfers heat from venous blood to arterial blood via a counter-current exchange system. This reduces surface cooling, maintaining warmer muscles. This supports higher swimming speed with reduced energy expenditure.[1]

Commercial fishing

Photo of larger than human-sized fish lying on a dock with fishermen in background
Tuna being weighed on Greek quay-side
Photo of large tuna being landed on fishing boat
Tuna fishing in Hokkaidō, Japan
Photo of multiple rows of tuna
Tuna at a fish market
Photo of split tuna resting on cutting machine
Tuna cut in half for processing at the Tsukiji fish market in Tokyo, Japan

Tuna is an important commercial fish. The International Seafood Sustainability Foundation compiled a detailed scientific report on the state of global tuna stocks in 2009, which includes regular updates. According to the report, 'Tunas are widely but sparsely distributed throughout the oceans of the world, generally in tropical and temperate waters between about 45 degrees north and south of the equator. They are grouped taxonomically in the family Scombridae, which includes about 50 species. The most important of these for commercial and recreational fisheries are yellowfin (Thunnus albacares), bigeye (T. obesus), bluefin (T. thynnus, T. orientalis, and T. macoyii), albacore (T. alalunga), and skipjack (Katsuwonus pelamis).[2]

The report further states:

Between 1940 and the mid-1960s, the annual world catch of the five principal market species of tunas rose from about 300 thousand tons to about 1 million tons, most of it taken by hook and line. With the development of purse-seine nets, now the predominant gear, catches have risen to more than 4 million tons annually during the last few years. Of these catches, about 68 percent are from the Pacific Ocean, 22 percent from the Indian Ocean, and the remaining 10 percent from the Atlantic Ocean and the Mediterranean Sea. Skipjack makes up about 60 percent of the catch, followed by yellowfin (24 percent), bigeye (10 percent), albacore (5 percent), and bluefin the remainder. Purse-seines take about 62 percent of the world production, longline about 14 percent, pole and line about 11 percent, and a variety of other gears the remainder 3.[2]

The Australian government alleged in 2006 that Japan had illegally overfished southern bluefin by taking 12,000 to 20,000 tonnes per year instead of the their agreed 6,000 tonnes; the value of such overfishing would be as much as USD $2 billion.[3] Such overfishing has severely damaged bluefin stocks.[4] According to the WWF, "Japan's huge appetite for tuna will take the most sought-after stocks to the brink of commercial extinction unless fisheries agree on more rigid quotas".[5] Japan's Fisheries Research Agency counters that Australian and New Zealand tuna fishing companies under-report their total catches of southern bluefin tuna and ignore internationally mandated total allowable catch totals.[6]

In 2010, a bluefin tuna weighing 232 kilograms (511.47 pounds) was sold at Tokyo's Tsukiji fish market for 16.28 million yen ($US 175,000).[7]

In early 2011, a new record was set at 32.49 million yen for a bluefin tuna weighing 754-pounds (342-kilograms), during an auction in Tsukiji Market, Tokyo. This equates to a whopping 95,000 yen per kilogram.[8]

Fishing methods

Association with whaling

In 2005 Nauru, defending its vote at that year's meeting of the International Whaling Commission, argued that commercial whaling is necessary for preserving tuna stocks and that country's fishing fleet.[10]

Association with dolphins

Dolphins swim beside several tuna species. These include yellowfin tuna in the eastern Pacific Ocean, but not albacore. Tuna schools are believed to associate themselves with dolphins for protection against sharks, which are tuna predators.[11]

Commercial fishing vessels used to exploit this association by searching for dolphin pods. Vessels would encircle the pod with nets to catch the tuna beneath.[12] however the nets were prone to entangling dolphins, injuring or killing them. Public outcry and new government regulations, which are now monitored by the NOAA have led to more "dolphin friendly" methods, now generally involving lines rather than nets. However, there are neither universal independent inspection programs nor verification of "dolphin safeness", so these protections are not absolute. According to Consumers Union, the resulting lack of accountability means claims that tuna that is "dolphin safe" should be given little credence.

Fishery practices have changed to be dolphin friendly, which has caused greater bycatch including sharks, turtles and other oceanic fish. Fishermen no longer follow dolphins, but concentrate their fisheries around floating objects such as fish aggregation devices, also known as FADs, which attract large populations of other organisms. Measures taken thus far to satisfy the public demand to protect dolphins can be potentially damaging to other species as well.[13]

Recreational fishing

From the 1950s through the 1970s, bluefin were abundant in the waters of Cuba, Bimini and Cat Cay, a few miles off the Florida coast, and were targeted by recreational fishermen, famously Ernest Hemingway and Habana Joe aboard his 1938 40-foot Wheeler named Pilar. Word spread quickly about the exciting new sport of big-game fishing. Despite the growing popularity of the sport, however, the boats of the day were hardly ideal for fighting the prized fish. Most boats used at the time were converted cabin cruisers, which were relatively slow and hard to maneuver.

The Rybovich family of South Florida eventually constructed a boat in 1946 that relaunched the sport and birthed a new industry. This boat, the Miss Chevy II, was the first sportfishing boat the world had ever seen.[14]

Merritt gained particular notoriety during the 1950s through the 1970s with its 37- and 43-foot custom boats, which together with boats like those being built by Rybovich, helped fuel the growth of big game fishing around the world.

Management and conservation

There are five main tuna fishery management bodies: the Western Central Pacific Ocean Fisheries Commission, the Inter-American Tropical Tuna Commission, the Indian Ocean Tuna Commission, the International Commission for the Conservation of Atlantic Tunas and the Commission for the Conservation of Southern Bluefin Tuna.[15] The five gathered for the first time in Kobe, Japan in January 2007. Environmental organizations made submissions[16] on risks to fisheries and species. The meeting concluded with an action plan drafted by some 60 countries or areas. Concrete steps include issuing certificates of origin to prevent illegal fishing and greater transparency in the setting of regional fishing quotas. The delegates are scheduled to meet at another joint meeting in January or February 2009 in Europe.[17]

In 2010, Greenpeace International has added the albacore, bigeye tuna, blackfin tuna, pacific bluefin tuna, northern bluefin tuna, southern bluefin tuna and the yellowfin tuna to its seafood red list. "The Greenpeace International seafood red list is a list of fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries."[18][19]

While many stocks are managed sustainably, it is widely accepted that bluefin have been severely overfished, with some stocks at risk of collapse.[20][21] According to the International Seafood Sustainability Foundation (a global, non-profit partnership between the tuna industry, scientists, and the World Wide Fund for Nature), Indian Ocean yellowfin tuna, Pacific Ocean (eastern & western) bigeye tuna, and North Atlantic albacore tuna are all overfished. In April 2009, no stock of skipjack tuna (which makes up roughly 60 percent of all tuna fished worldwide) was considered to be overfished.[22]

Aquaculture

Increasing quantities of high-grade tuna are reared in net pens and fed bait fish. In Australia, former fishermen raise southern bluefin tuna, Thunnus maccoyii, and another bluefin species.[9] Farming its close relative, the northern bluefin tuna, Thunnus thynnus, is beginning in the Mediterranean, North America and Japan. Hawaiʻi just approved permits for the first U.S. offshore farming of bigeye tuna in water 1,300 feet (400 m) deep.[23]

Japan is the biggest tuna consuming nation and is also the leader in tuna farming research.[24] Japan first successfully farm-hatched and raised bluefin tuna in 1979. In 2002, it succeeded in completing the reproduction cycle and in 2007, completed a third generation.[25][26][27] The farm breed is known as Kindai tuna. Kindai is the contraction of Kinki University in Japanese (Kinki daigaku).[28] In 2009, Clean Seas, an Australian company which has been receiving assistance from Kinki University [29][30][31] managed to breed Southern Bluefin Tuna in captivity and was awarded the second place in World's Best Invention of 2009 by Time magazine.[32]

Canned tuna

Photo of grocery shelves
Canned tuna on sale at an American supermarket
Photo of plate containing grilled tuna and leafy vegetables
Tuna steak served in a French bistro

Canned tuna was first produced in 1903, quickly becoming popular.[33] Tuna is canned in edible oils, in brine, or spring water. In the United States, 52% of canned tuna is used for sandwiches; 22% for salads; and 15% for casseroles and helpers.[34]

In the United States, only Albacore can legally be sold in canned form as "white meat tuna";[35] in other countries, yellowfin is also acceptable. While in the early 1980s canned tuna in Australia was most likely Southern bluefin, as of 2003 it was usually yellowfin, skipjack, or tongol (labelled "northern bluefin").[33]

As tuna are often caught far from where they are processed, poor quality control leads to spoilage. Tuna are typically eviscerated by hand, then pre-cooked for 45 minutes to three hours. The fish are then cleaned and filleted, canned, and sealed. The sealed can itself is then heated (called retort cooking) for 2 to 4 hours.[36] This process kills any bacteria, but retains the histamine that can produce rancid flavors. The international standard sets the maximum histamine level at 200 milligrams per kilogram. An Australian study of 53 varieties of unflavored canned tuna found none to exceed the safe histamine level, although some had "off" flavors.[33]

Australian standards once required cans of tuna to contain at least 51% tuna, but these regulations were dropped in 2003.[37][38] The remaining weight is usually oil or water. In the US, the FDA regulates canned tuna (see part c).[39] In 2008, some tuna cans changed from 6 ounces (170 g) to 5 ounces (140 g) due to "higher tuna costs".[40]

Nutrition and health

Canned tuna is a prominent component in many weight trainers' diets, as it is high in protein and easily prepared.

Tuna is an oily fish, and therefore contains a high amount of Vitamin D. A can of tuna in oil contains about the Adequate Intake (AI) of the US Dietary Reference Intake of vitamin D for infants, children, men, and women aged 19–50 - 200 IU.

Canned tuna can also be a good source of omega-3 fatty acids. It sometimes contains over 300 milligrams (0.011 oz) per serving.[41]

Mercury levels

Mercury content in tuna can vary widely. For instance, testing by Rutgers University found that a can of StarKist had 10 times more mercury than another can of exactly the same kind of tuna. This has prompted a Rutgers University scientist whose staff conducted the mercury analysis to say, "That's one of the reasons pregnant women have to be really careful ... If you happen to get a couple or three cans in the high range at a critical period when you are pregnant, it would not be good." Among those calling for improved warnings about mercury in tuna is the American Medical Association, which adopted a policy that physicians should help make their patients more aware of the potential risks.[42]

A study published in 2008 found that mercury distribution in tuna meat is inversely related to the lipid content, suggesting that the lipid concentration within edible tuna tissues has a diluting effect on mercury content.[43] These findings suggest that choosing to consume a type of tuna that has a relatively higher natural fat content may help reduce the amount of mercury intake, compared to consuming tuna with a low fat content.

The industry-sponsored group Center for Consumer Freedom, which doesn't release the names of its contributors, claims the health risks of methylmercury in tuna might be dampened by the selenium found in tuna,[44] although the mechanism and effect of this still is largely unknown.[45]

Due to their high position in the food chain and the subsequent accumulation of heavy metals from their diet, mercury levels can be high in larger species such as bluefin and albacore.

In 2009 a California appeals court upheld a ruling that canned tuna does not need warning labels as the methylmercury is naturally occurring.[46]

In March 2004 the United States FDA issued guidelines recommending that pregnant women, nursing mothers, and children limit their intake of tuna and other predatory fish.[47]

In 2007 it was reported that some canned light tuna such as yellowfin tuna[48] is significantly higher in mercury than skipjack, and caused Consumers Union and other activist groups to advise pregnant women to refrain from consuming canned tuna.[49] This was considered extreme and thus not adopted by leading scientific and governing bodies.

The Eastern little tuna (Euthynnus affinis) has been available for decades as a low-mercury, less expensive canned tuna. However, of the five major species of canned tuna imported by the United States it is the least commercially attractive, primarily due to its dark color and more pronounced 'fishy' flavor. Its use has traditionally been restricted to institutional (non-retail) commerce./p>

A January 2008 investigation conducted by the New York Times found potentially dangerous levels of mercury in certain varieties of sushi tuna, reporting levels "so high that the Food and Drug Administration could take legal action to remove the fish from the market."

 


Tuna Selection and Storage

Freeze fresh tuna in a water-bath

tuna recipes albacore yellowfin ahi canned seafood receipts

Tuna Selection and Storage

The flesh of the tuna can range from very light pink (nearly white) to deep reddish brown, depending on the variety. Prime raw tuna steaks look very much like raw beef, right down to the deep red color of the flesh. The tuna steak may have a darker brown area, which is edible but has a much stronger flavor. Sometimes this is already trimmed away by the fishmonger. Fresh tuna is usually sold already skinned since the skin is extremely tough.

When selecting fresh tuna, avoid any with dry or brown spots (other than the natural darker brown area). There should be no rainbow sheen on the fish, and it should smell ocean-fresh. The fishmonger generally keeps the tuna in a large filet, which looks very much like a beef loin, and will slice off what you need.

Fresh tuna season runs from late spring to early fall, but frozen steaks are available year-round.

If you have the option, skip the thawed frozen filets and buy the tuna filet frozen. This way, you know it will be the freshest possible because you control when to thaw it. Just be sure to store it in the coldest part of your freezer until you are ready to thaw it.

Get that raw tuna home from the market and into your refrigerator as soon as possible. Keep the tuna refrigerated until you are ready to use it. It is best to use fresh tuna the day of purchase.

If you need to store it, pat it dry, wrap securely in plastic wrap or foil and store in the coldest part of your refrigerator (optimum temperature of 31 degrees F.). If your refrigerator is not that cold, place the wrapped fish on a bed of ice or in a plastic bag filled with ice. Use within 24 hours.

If you know the tuna is fresh and not previously frozen, feel free to wrap and freeze it. However, if you're buying fresh tuna in a grocery store, you can almost bet it has been previously frozen, in which case it is best to use it immediately.

To freeze fresh tuna, prepare a solution of 1 tablespoon ascorbic acid crystals to 1 quart of water or 1/4 cup salt dissolved in 1 quart of water. Dip the fish into the solution to firm it up. Seal in plastic wrap and then in a zip-top bag.

Better yet, freeze it in an ice block by putting into a zip-top bag and covering with water. Squeeze out all the air and seal the bag. Freeze up to three months.

Thaw frozen tuna slowly in the refrigerator. If it is in a sealed zip-top bag, it can be thawed more quickly by placing the sealed package in a sink or pot of cold water. Microwave thawing is not recommended.

Cooked fish will keep three to four days in the refrigerator. Leftover cooked tuna is excellent as a salad topper. Reheating is not recommended, unless you chop and add gently at the end of a cream sauce until just warmed through. Serve over rice or pasta.

Whole chunks of smoked tuna will last up to ten days in the refrigerator. Be sure it is always kept tightly wrapped. Smoked tuna chunks can be wrapped and frozen up to two months, but be aware that there may be some loss of texture when thawed.

Canned Tuna

You will have many varieties and grades of canned tuna from which to choose. Your selection will depend on your tastes and the specific recipe used. Solid or fancy pack will contain large pieces of tuna and is usually albacore. Only albacore tuna may be labeled and sold as white tuna. Many will pay the higher price for white tuna because it has a milder flavor and lighter color. In fact, it looks very much like canned chunk chicken and can be substituted for canned chicken in many recipes.

Chunk tuna has smaller pieces. Flaked tuna is fairly broken apart and best used for salads where the tuna is mashed and mixed anyway.

Canned tuna is usually packed in water or oil, with the oil-packed being more flavorful and moist. The latest commercial innovation is tuna packed in vacuum pouches with no added oil or water.

Unopened canned tuna can be stored in a cool cupboard up to 1 year. Place leftover canned tuna in a sealed container in the refrigerator and use with four days. Tuna salad with a dressing can be refrigerated up to three days. Cooked tuna dishes such as casseroles can be frozen up to 2 months.

Tuna Cooking Tips and Hints

• That little bit of fat and strong flavor also make tuna a perfect choice for smoking. Fresh tuna is often compared to beef steak, due to the beautiful red color and meat-like texture.

• Sushi-grade tuna has usually been flash-frozen within a couple of hours of being caught. Thawed fresh-frozen tuna generally does not degrade in flavor or texture as compared to fresh off the boat, so do not hesitate to buy it frozen from any reputable market.

• The finest tuna is reserved for eating raw, as in sushi or sashimi. If you are cooking fresh tuna at home, it should ideally be cooked medium-rare, seared very quickly over high heat, preferably on a grill. If you cannot handle medium-rare tuna, at least do not overcook it. Cook until the flesh changes color and is no longer translucent. Overcooking will dry out and ruin that pricey culinary investment.

• Canned tuna is called tunafish (note no space in between). It is a cupboard staple in most households. One drained 6-ounce can yields 2/3 to 3/4 cup of flesh for measuring purposes, although it can vary depending on the supplier.

• You will find canned tuna packed in oil, water or even flavored sauces. The liquid is drained before using for most applications. For richer and more flavorful broths and sauces, incorporate the liquid from the canned tuna into the recipe if your diet permits it.

• Tuna can be substituted in most salmon recipes, both canned and fresh.

Tuna Varieties

There are a number of varieties of tuna, with flesh ranging from light to dark. Tuna varieties include albacore, tunny, ahi, bonito, skipjack, bigeye, bluefin, and yellowfin.

Bluefin tuna: This is generally the variety of choice for fresh tuna connoisseurs. It has a bit more fat, thus more flavor, than the other varieties. At maturity, the flesh is dark red, with an appearance very similar to raw beef. This variety is the largest, growing up to 1,600 pounds. Most of the bluefin harvest is exported to Japan and sold at a premium price for sashimi.

Yellowfin tuna: Also known as ahi. Less expensive than bluefin, this variety is nearly as good as bluefin and also more common and easy to find in the markets. It is pale-pink, with flavor a bit stronger than albacore. It is also often canned.

Skipjack tuna: Also known as bonito and aku. As you can surmise from its name, this fish likes to jump and skip over the surface of the ocean. This variety is usually canned. It generally has the strongest flavor and highest fat content. It is also the smallest variety, seldom growing larger than 25 pounds. Dried bonito is known as katsuobushi and is used in Japanese cuisine.

Albacore tuna: This is the variety with the lightest flesh and mildest flavor. It's usually canned as white tuna and sold at a higher price than light chunk tuna.

Tuna Health

Fresh tuna has only one percent fat per body weight, making it a favored choice for those on low-fat diets. However, the depth of the water and water temperature will affect the fat content of the fish. This fat content can vary not only from catch to catch but also between different varieties of tuna.

For example, two cans of water-packed white tuna of equal size, even from the same company, can vary from in content from 1 to 5 grams of fat per 2-ounce serving. Due to this interesting scientific fat variation, it is actually possible for tuna packed in water to have more fat than tuna packed in oil. Amazing, but true, and yet another reason to always check the label on every canned tuna purchase if you must control your fat intake.

If you are looking to boost your Omega-3 fatty acids (famous for fighting heart disease), choose canned albacore, which often contains not only more Omega-3 fatty acids than the chunk light canned, but also more than even fresh tuna.

For those allergic to soy, be aware that most tuna packed in oil has added soybean oil. Canned tuna packed in olive oil is available in most markets, although it is usually more expensive. Most canned tuna fans prefer the olive oil-packed tuna above all others for flavor. Luckily, olive oil is heart healthy. The oil actually leeches out some of the cholesterol. Drain and gently rinse off the oil if you must.

 

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