Tuna: Description, Species, Lifestyle, Habitat, and Reproduction

Tuna: Description, Species, Lifestyle, Habitat, and Reproduction. Tuna is one of the fastest and most powerful marine predators of the Scombridae family. Its name comes from the Greek word "thunnos," meaning "to rush" or "to hurl," and perfectly reflects the behavior of this fish: tuna can reach speeds of up to 80–85 km/h, and its body is ideally adapted for long migrations and swift attacks. This is a valuable commercial species, whose meat is highly prized for its tenderness, fatty content, and rich chemical composition. Tuna is a classic marine inhabitant, unlike the freshwater predators of the Putorana Plateau, where the fish also reach impressive sizes thanks to the pristine water and abundant food supply.

Description of the species

The tuna's body is elongated and torpedo-shaped, tapering toward the tail and having a nearly circular cross-section. The head is cone-shaped, with two small eyes on each side and a large mouth equipped with a single row of sharp teeth. The first dorsal fin is concave and elongated, while the second is thin and sickle-shaped, similar to the anal fin. A row of small finlets extends from the second dorsal and anal fins to the tail—9-12 on the upper fin and 8-9 on the lower fin.

The tail fin is sickle-shaped and powerful, enabling high speed and maneuverability. Tuna are forced to constantly move: if they stop, their gill covers will stop working, and the fish will simply suffocate. Tuna's body temperature is higher than the surrounding water—up to 36–37°C—thanks to their well-developed circulatory system, allowing them to maintain high activity even in cold waters.

The average lifespan of large species is up to 35 years, small ones – less than 10 years.

In order for tuna to be able to breathe, it needs to constantly move, otherwise the gill covers will not open and enrich the blood with oxygen.

Weight and size of tuna

Tuna are striking in size. Small species reach only 30–40 cm and weigh 2–3 kg, but true giants—bluefin tuna—grow up to 4–4.5 meters in length and weigh over 600 kg. Record specimens exceed 700 kg. Size depends on the species, habitat, and food supply: in tropical waters, the fish grows faster and reaches its maximum size.

Tuna is one of the most impressive fish in the world's oceans, in terms of size and mass. The range of sizes between species is enormous: from small schooling fish to true marine giants whose mass and length rival the largest freshwater predators. For comparison, even record-breaking tuna specimens approach the mass and strength of the largest taimen found in the rivers of the Putorana Plateau, despite the vastly different habitats and lifestyles of these fish.

Record-breaking specimens

The largest documented tunas are of the bluefin (common) species:

• 1979, Atlantic (Nova Scotia, Canada) - 678 kg with a length of 4.5 m
• 1979, Atlantic — 679 kg
• Later data (2000s) - individual specimens exceeded 700 kg, but officially confirmed records remain in the region of 680-700 kg

Is tuna a red or white fish?

Tuna meat ranges from a delicate pink to a rich scarlet and even brown. This is due to its high content of myoglobin, an oxygen-binding protein that accumulates in the muscles due to constant movement. Myoglobin contains a lot of iron, so dark meat is especially rich in this element (up to 11 mg per kg).

Light meat is more tender and fatty, dark meat is looser and more watery, but no less healthy.

Does tuna have scales?

Tuna have scales, but they are uneven. The scales on the front and sides of the body are large and thick, forming a kind of protective armor. The rest of the body has small scales. Scale coloration varies by species: often dark on the back and light on the belly, sometimes with stripes or unusual hues.

What does tuna eat?

Tuna are active predators, feeding on everything found in the ocean. Larger species hunt at mid-depth and can even consume small sharks, squid, octopus, and flounder. Smaller species stay near the surface and feed on schooling fish, mollusks, crustaceans, and sponges.

Tuna always hunt in schools and can follow schools for vast distances, even entering cold waters. The intense accumulation of mercury in their meat is due not only to their diet but also to anthropogenic ocean pollution (oil, industrial discharges), as well as natural sources (volcanoes, rock weathering).

The main diet of this predator:

• many species of schooling fish, including herring, hake, pollock;
• squid;
• octopuses;
• flounder;
• mollusks;
• various sponges and crustaceans.

Tuna accumulates mercury in its flesh more than any other marine animal, but the main reason for this is not its diet, but human activity, which introduces this dangerous element into the water. Some mercury ends up in the ocean during volcanic eruptions and through the weathering of rocks.

One seafarer captured the moment when a particularly large tuna snatched a seagull from the surface of the water and swallowed it, but after a while spat it out, realizing its mistake.

Chemical composition of tuna meat

Tuna is a source of complete protein (95% digestible) and healthy fats (poly- and monounsaturated, omega-3, and omega-6). It contains virtually no carbohydrates. 100 g contains nearly the daily requirement of many elements: cobalt, chromium, niacin, pyridoxine, phosphorus, iodine, thiamine, sulfur, potassium, iron, calcium, zinc, magnesium, copper, selenium, and vitamins A, B, C, D, H, and PP.

The recommended serving is 100–150 g no more than 1–2 times a week.

Tuna combines the qualities of both red and white fish: high levels of myoglobin (like beef) and a huge amount of omega-3 (like salmon or mackerel). It also contains virtually no carbohydrates and has a very high biological value of protein—a digestibility rate of 95–98%.

Tuna meat is a real natural concentrate of protein, essential fatty acids and microelements.

The benefits and harms of tuna for the body

The benefits of tuna are enormous:

• Reduces the risk of cancer
• Supports the cardiovascular system, strengthens the walls of blood vessels
• Stabilizes blood pressure and eliminates arrhythmia
• Prevents liver and kidney diseases
• Relieves inflammation in arthritis
• Prevention of Alzheimer's disease
• Helps with dermatitis and allergies
• Stimulates the brain, vision, fertility
• Lowers cholesterol
• Useful for depression
• Cleanses the liver of toxins
• Normalizes metabolism
• Strengthens the immune system, improves the condition of skin, nails and hair

Harmful effects and contraindications are associated with the accumulation of heavy metals (mercury, lead) due to ocean pollution. Not recommended for children under 3 years of age or for pregnant or breastfeeding women. High purine content can trigger gout or kidney stones. Avoid this product completely if you have an allergy or intolerance.

Social structure and reproduction

Tuna reach sexual maturity at 3 years of age, but typically spawn at 10–12 years (earlier in warmer waters). Their lifespan is up to 35–50 years. Spawning occurs in warm waters (23–27°C): the Gulf of Mexico, the Mediterranean Sea, and different zones have different timings.

The female spawns up to 10 million eggs (approximately 1 mm in diameter), fertilized externally. The fry hatch after a few days, staying near the surface and feeding on plankton and crustaceans. They gradually transition to an adult diet and join the schools.

Tuna always live in schools—solitary fish are rare (only scouts). There is no hierarchy, but the school's actions are coordinated.

Where does tuna live?

Tuna are found throughout almost all of the world's oceans, except for polar waters. They prefer the tropical and subtropical zones of the Atlantic, Pacific, and Indian Oceans. They can enter cold waters, but prefer warmer waters.

Bluefin tuna were once found from the Canary Islands to the North Sea, and occasionally in Norway, the Black Sea, Australia, and Africa. Their range has now shrunk due to overfishing.

Most species stay away from the coast, except for the Australian bluefin tuna, which remains close to the coast. Migration follows feeding schools—in the spring to the shores of the Caucasus, Crimea, and the Sea of Japan (until October), and in the winter to deeper waters.

In Russia, tuna fishing is limited due to the lack of modern tuna fishing vessels. Stores often import tuna from China and Vietnam.

Unlike sea tuna, the fresh waters of the Putorana Plateau are home to powerful predators— taimen, lenok, and char—which also migrate and reach impressive sizes in the crystal-clear rivers and lakes.

Types of tuna

Of the more than 60 species, the following 12 species are most significant for trade and science:

Atlantic (blackfin, black) tuna

The Atlantic tuna, also known as the blackfin tuna or blackfin tuna (Latin: Thunnus atlanticus), is one of the most striking representatives of the tuna genus in the Scombridae family. It is a relatively small, yet extremely fast and active marine predator, highly prized in fishing and cooking for its dense, tender, and moderately fatty meat. Unlike the giant bluefin or yellowfin tuna, the blackfin tuna remains more compact, yet retains all the key characteristics of a true tuna: incredible speed, constant movement, and life in large schools.

The blackfin tuna's body is elongated, torpedo-shaped, and strongly compressed laterally at the rear. The maximum length of an adult is 110–120 cm, with fish typically caught at 60–90 cm. Their weight rarely exceeds 20–25 kg, with the average commercial weight being 8–15 kg.

Bluefin tuna

Bluefin tuna, also known as bluefin tuna or common tuna (Latin: Thunnus thynnus), is the largest and most powerful fish of the tuna genus and one of the most impressive marine predators on the planet. A true king of the open ocean, capable of reaching speeds of 70–85 km/h, completing transatlantic migrations of thousands of kilometers, and reaching a mass comparable to a small car, bluefin tuna are a legend among fishermen and the object of intense scientific and commercial attention.

The bluefin tuna's body is massive, torpedo-shaped, and perfectly streamlined. The head is cone-shaped, the mouth large, with a single row of sharp teeth. The eyes are relatively small but very sharp. The first dorsal fin is long and high, while the second is short and sickle-shaped. The anal fin is also sickle-shaped. Eight to ten small finlets extend from the second dorsal and anal fins to the tail, extending from the dorsal and ventral fins.

Yellowfin tuna

Yellowfin tuna (Thunnus albacares) is one of the most common and commercially exploited tuna species, also known as yellowfin tuna. It is a large, powerful, and incredibly fast marine predator that plays an important role in global fisheries and cuisine. Yellowfin tuna is prized for its firm, tender meat with a distinct flavor and high content of healthy fats. Unlike the giant bluefin tuna, yellowfin tuna is more abundant and readily available, yet retains all the key characteristics of true tuna: speed, extensive migrations, and life in large schools.

Bigeye tuna

The bigeye tuna (Thunnus obesus) is one of the most interesting and largest tuna species in the Scombridae family. It gets its name from its enormous eyes, which allow it to navigate and hunt perfectly even at significant depths where little light penetrates. It is a deep-sea and extremely powerful predator that leads a more stealthy lifestyle than surface species such as yellowfin or skipjack tuna. Bigeye tuna meat is highly prized for its firm texture, rich flavor, and high content of healthy fats.

Albacore (albacore, white tuna)

Albacore, also known as albacore or white tuna (Latin: Thunnus alalunga), is one of the most prized and recognizable members of the tuna family. It is often called "white tuna" due to its lightest and most tender meat of all tuna species, and "albacore" due to its extremely long pectoral fins, which in adults can reach almost to the anus. Albacore is highly prized in cooking for its exquisite flavor, high fat content, and firm texture—its meat is most often used in premium canned goods and for making high-end sushi/sashimi. The albacore's body is elongated, torpedo-shaped, with smooth contours and a nearly circular cross-section in the middle. The head is relatively small and cone-shaped, the mouth is wide, with a single row of sharp teeth. The eyes are large, well-adapted for hunting at dusk and in deep water.

Skipjack tuna

Skipjack tuna (Katsuwonus pelamis) is one of the most abundant and widespread tuna species in the Scombridae family. It is this tuna that is most often found in canned goods under the names "tuna in its own juice" or "tuna in oil"—its meat forms the basis of most budget and mid-price tuna products worldwide. Skipjack is a small but incredibly fast and active pelagic predator that lives in huge schools and is characterized by high fertility and rapid growth. The skipjack's body is elongated, torpedo-shaped, with smooth contours and a nearly circular cross-section in the middle. The head is relatively small and conical, with a wide mouth containing small, sharp teeth. The eyes are medium in size.

Australian tuna

The Indo-Pacific bluefin tuna (Thunnus tonggol), also known as the Indo-Pacific albacore or Indian bluefin tuna, is a relatively little-studied but highly commercially important species of the Scombridae family. This tuna occupies a unique position among its relatives: it is primarily coastal, rarely ventures far into the open ocean, and is most often found in waters adjacent to continental shelves. This makes the Indo-Pacific bluefin tuna one of the most accessible species for local fisheries in Southeast Asia and Australia.

The Australian tuna's body is elongated, torpedo-shaped, with smooth contours and slightly laterally compressed. The head is cone-shaped, the mouth large, with a single row of sharp teeth. The eyes are medium-sized, well adapted for hunting both near the surface and at mid-depths.

Albacore tuna

Albacore tuna (Thunnus alalunga), also commonly known as albacore or white tuna, is one of the most prized and recognizable tuna species in the Scombridae family. It gets its name from its exceptionally long pectoral fins, which in adults can reach almost to the anus. This tuna is most often associated with the term "white tuna"—its flesh is the lightest, most tender, and fatty of all tuna species, making it a premium product in cooking and canning.

Southern bluefin tuna

The southern bluefin tuna (Thunnus maccoyii) is one of the largest and most powerful tuna species in the Scombridae family. It is a distinct species, closely related to the northern bluefin tuna, but has its own distinct range, a more southern distribution, and a number of biological differences. The southern bluefin tuna is a true legend of the Southern Hemisphere, an object of intense fishing and strict protection, as its population suffered greatly from overfishing in the 20th and 21st centuries.

The southern bluefin tuna's body is massive, torpedo-shaped, and perfectly streamlined. Its head is cone-shaped, its mouth large, and its single row of sharp teeth. Its eyes are relatively small but very sharp.

Mackerel tuna

The mackerel tuna (Auxis thazard and Auxis rochei) is one of the smallest and most abundant members of the mackerel family, a close relative of the true tunas of the genus Thunnus. It is often called "mackerel tuna" or "frigate tuna" due to its resemblance to mackerel and its high swimming speed. It is a small but extremely active pelagic predator that forms huge schools and plays an important role in tropical and subtropical ocean ecosystems. Mackerel tuna is a major target for local fisheries in the tropics, and its meat is widely used in canned and fresh fish.

Spotted tuna

The spotted tuna ( Euthynnus affinis, also known as the kawakawa, eastern spotted tuna, and mackerel tuna) is one of the most widespread and commercially exploited members of the scombrid family in the Indo-Pacific region. It is a small but extremely fast and active pelagic predator that forms huge schools and plays an important role in tropical ecosystems. Spotted tuna is highly prized in local fisheries in Southeast Asia, India, Australia, and Oceania due to its firm, flavorful, and moderately fatty meat, which is excellent for both fresh cooking and canning.

The spotted tuna's body is elongated, spindle-shaped, and laterally compressed, very similar to that of mackerel and skipjack tuna. The head is cone-shaped, and the mouth is medium-sized with small, sharp teeth. The eyes are large, well-adapted for hunting near the surface and at dusk.

Eastern tuna

The eastern tuna (Euthynnus affinis), also known as the eastern spotted tuna, kawakawa, or maki tuna, is one of the most widespread and abundant species of the scombridae family in the Indo-Pacific region. It is a small but extremely fast and active pelagic predator that forms huge schools and plays a key role in tropical ecosystems. Eastern tuna is highly prized in the local fisheries of Southeast Asia, India, Australia, and Oceania due to its firm, flavorful, and moderately fatty meat, which is excellent for both fresh cooking and canning.

Conclusion

Tuna is a symbol of the ocean's power and a prized trophy. Catching it requires powerful gear, knowledge of migration patterns, and respect for nature. Unlike the freshwater giants of the Putorana Plateau, tuna remains the king of the sea, where speed, power, and migration define its entire life.