What You Should Know About Tuna

Tuna Trivia
Scientific name: Thunnini

Fresh Tuna Steak

Known for their distinct flavor, global availability and versatility in the kitchen, tuna fish has risen to be one of the most consumed fish on the market today. It’s even recommended as a “replacement” for red meat, which is why some people believe that it is safe to eat tuna every day.

But there are alarming pitfalls to eating tuna, and if you’re not careful, you can fall victim to its damaging effects. Read this article and learn important facts about this seafood: why it is not advisable for human consumption, the fraud behinds its commercialization and the dangers it poses to your health.

What Is Tuna?

Tuna is a marine fish that belongs to the mackerel (Scombridae) family, similar to albacore and bonito, but specifically falls under the sub-group or “tribe” called Thunnini.1 There are several species of tuna, all of which are nomadic – they do not spend their whole lives in one place, and instead change their location frequently. Most tuna species today are found in the subtropical and temperate waters of the Atlantic Ocean, Mediterranean Sea and Black Sea.2

Tuna fish can grow to very large sizes. For example, the Atlantic blue fin tuna can grow to a whopping 2 meters (6.5 feet) long, weighing 250 kilograms (550 pounds).3 But there are larger specimens recorded. In fact, the largest ever recorded tuna was 21 feet long, with a weight of 1,600 pounds.4

Despite their large size, tunas are very agile and can swim very fast, covering long distances at high speeds. They can swim at speeds up to 62 miles per hour. Tunas are carnivores, and usually feed on squids, crustaceans and different types of smaller fish like herring, hake and mackerel.5

The Different Types of Tuna

There are at least 15 different species of tuna fish,6 each with their distinct characteristics. However, there are only five species most consumers are familiar with:7

Skipjack tuna (Katsuwonas pelamis) – Of all the commercial tuna species, this is the smallest and most abundant. Skipjacks are known for their streamlined bodies that do not have scales, with their backs having a dark purple-blue coloring. Their lower sides and bellies are both silver, and if you look closer, you’ll notice four to six dark bands.

Skipjack tuna mainly reside in the Indian, Atlantic and Pacific Oceans, with the majority residing near the equator. They can live for eight to 10 years. Skipjack are also the main species used for canned tuna.

Yellowfin tuna (Thunnus albacares) – You can distinguish yellowfin by their yellow sides, silver belly and torpedo-shaped backs that are a dark metallic blue color. Their finlets are bright yellow, and they have very long anal and dorsal fins. This species can live up to six or seven years, and are highly migratory. Yellowfins reside throughout the Atlantic, Pacific and Indian Oceans.

Bluefin tuna (Thunnus maccoyii, Thunnus orientalis and Thunnus thynnus) – Not only are bluefins the largest species, but they’re also the most long-lived, with some living up to 40 years. They’re made for speed: their built can be likened to torpedoes, their eyes are set flush to their body and their fins are retractable.

There are three species of bluefins: Southern (Thunnus maccoyii), Atlantic (Thunnus thynnus) and Pacific (Thunnus orientalis). Of these three, the Atlantic is the most endangered. In addition, Bluefin tunas are tremendous predators (which explain their large size), often beginning hunting the moment they hatch. They usually seek schools of fish like mackerel and herrings and even eat eels.

Bigeye tuna (Thunnus obesus) – This species is also long-lived, reaching up to 10 to 12 years old. Bigeyes reside in the tropical and subtropical regions of the Indian, Pacific and Atlantic Oceans (but not the Mediterranean Sea). They can be identified by their long and streamlined appearance, with a dark metallic blue color on their upper sides and back, and white lower sides and belly.

Albacore tuna (Thunnus alalunga) – Albacore can be identified by their very long pectoral fins and bullet-shaped body. They’re smaller than other species, and are usually as large as skipjack and yellowfins. They have a dark blue back, and lighter blue-gray sides and belly.

Albacores migrates through all ocean waters, including the Mediterranean. They usually travel in single species schools, unlike other tunas that usually mix with other species.

Because this fish family is likely the most widely commercially harvested of all fish today – with France, Japan, the U.S., Spain and Taiwan as the top harvesters – there’s growing concerns about the longevity of tuna.8

A major concern surrounding tuna is its mercury contamination. Like many large fish species, tuna accumulates mercury, a heavy metal that is toxic to neurons in the brain.

The Dangers of Tuna Consumption: Watch Out for High Mercury Levels in These Fish

Tuna actually contains a wide array of vitamins, minerals and nutrients, including antioxidants, proteins, selenium, potassium and iron, to name a few.9 But unfortunately, its high mercury levels far outweigh its potential health benefits, and is the primary reason why tuna is not recommended for human consumption.

High levels of mercury exposure can cause damage to the brain, kidneys, heart, lungs and immune system of people of all ages. However, it’s particularly damaging to unborn babies and young children, as it may interfere with their developing nervous system, causing them to have poor cognitive function.10 For this reason, the FDA advises pregnant women not to eat tuna to avoid passing on its damaging effects on their unborn child.11

According to a research published in 2010, which looked at the contributions to total mercury in U.S. seafood (from 51 different shellfish and fish varieties), tuna was found to be responsible for over one-third of Americans’ total exposure to methylmercury.12

What’s more, a study from the U.S. Geological Survey revealed that ALL tuna tested contained fairly high amounts of mercury.13

There’s no telling how much tuna is actually safe to eat – remember that mercury is extremely toxic, so ideally you should not be exposed to any. What’s more, methylmercury harms people’s nervous systems to differing degrees, depending on how much mercury they have accumulated.

And if you think that you cannot get mercury poisoning from tuna served in fancy restaurants, think again – studies show that the contamination is worse in these establishments. Toxicology testing found that levels of mercury in tuna served in restaurants are actually higher compared to store-bought varieties.

This is because restaurants tend to choose certain tuna species, such as bigeye and bluefin akami, which contain higher mercury levels than other species like yellowfin and bluefin toro. Bigeye and bluefin akami are leaner – but because mercury accumulates to a greater degree in muscle than fat, this means that these highly prized varieties contain more mercury.14

Another alarming fact about tuna is that it is often mislabeled. According to the conservation group Oceana, almost 60 percent of the fish labeled “tuna” in the U.S. is not tuna but is instead cheaper common fish varieties. Sushi restaurants are particularly large offenders, as 84 percent of the “white tuna” they sell is actually escolar, a fish that’s been linked to acute and serious digestive problems, even if consumed in small amounts.15

Tuna Nutrition Facts

In a perfect world, people would be able to get all the important nutrients below from tuna and other seafood. Unfortunately, the risk of mercury exposure is much too great to recommend this food for consumption. This is quite saddening, because tuna, if clean and untainted with heavy metals, can provide you with a wide array of nutrients.

Tuna Nutrition Facts

Serving Size: 100 grams
  Amt. Per
Serving
% Daily
Value*
Calories 108 5%
Calories from Fat 8.6  
Total Fat 0.9 g 1%
Saturated Fat 0.2 g 1%
Trans Fat    
Cholesterol 45 mg 15%
Sodium 37 mg 2%
Total Carbohydrates 0 g 0%
Dietary Fiber 0 g 0%
Sugar 0 g  
Protein 23.4 g 47%
Vitamin A 1% Vitamin C 2%
Calcium 2% Iron 4%

*Percent Daily Values are based on a 2,000 calorie diet. Your daily values may be higher or lower depending on your calorie needs.

Instead of tuna, opt for safer seafood varieties like wild Alaskan salmon, which come from waters that are not tainted with mercury. Smaller fish like sardines and anchovies also pose a low mercury risk because their small bodies do not accumulate mercury.