Species T. thynnus, T. orientalis, T. maccoyii
Bluefin Tuna Basics
Bluefin tuna is a collective term for three closely related tuna species called the Atlantic, Pacific, and Southern bluefin tuna. The Atlantic bluefin tuna (Thunnus thynnus) is the largest and most prevalent species, reaching lengths of up to ten feet and weighing up to 1,500 pounds. Although the Pacific bluefin tuna (Thunnus orientalis) and the Southern bluefin tuna (Thunnus maccoyii) are intimately related, their distributions and ranges are completely distinct.
Bluefin Tuna Description
Bluefin tunas are a kind of predatory fish with an elongated, streamlined body and a torpedo-like shape. The Atlantic bluefin may reach astonishing proportions, weighing up to 1,500 pounds and measuring up to 10 feet in length. Their tails are long, and they have a conical head with a wide mouth, as well as a dorsal and anal fin. In comparison to other tuna species, bluefins have two rather short pectoral fins. They have little finlets along their rear region, similar to other tuna, between their dorsal and anal fins and their tail fin. They are typically a mixture of blue tones that fade to a silvery hue on the underbelly of the animal.
Bluefin Tuna Distribution and Habitat
The Atlantic bluefin tuna may be found in both the Atlantic and Mediterranean Seas. They were formerly found in the Black Sea, but have since become extinct. Pacific bluefin tuna are widespread across the Pacific Ocean, including recognised spawning grounds in the Philippine Sea and the Sea of Japan. Additionally, they have been reported to migrate to the East Pacific and further, but after many years, they will return to their spawning grounds. Southern bluefin tuna may be found across the southern hemisphere, including a recognised breeding zone in the Indian Ocean near the Indonesian island of Java.
Bluefin tuna are oceanic fish that spend most of their time at depth in offshore waters. Unlike yellowfin tuna, which pass the majority of their time on the top, the majority of bluefin tuna are reported to dive regularly to depths of over 3,000 feet.
Bluefin Tuna Diet
Bluefin tuna are aggressive fish that target a variety of prey using their power and skill. Sardines and mackerel, which are smaller schooling fish, are often targeted. Herring and juveniles of larger fish, including other tuna, are also frequently consumed. Bluefins may pursue squid at depths during the day or at shallower depths during the night as the squid rise to forage for themselves. Squid are among the invertebrate species that bluefins devour. Crabs, lobsters, crayfish, and shrimp, as well as other pelagic crustaceans, are frequent prey for bluefin tuna.
Bluefin Tuna Reproduction
Like other tuna species, bluefin tuna reproduce in certain areas across the year based on the species and population. For example, in the western Atlantic, the Atlantic bluefin tuna spawns in just two locations: the western Mediterranean Sea and the Gulf of Mexico. Females may generate up to 30 million eggs at a moment, which they distribute throughout the water column with the help of males, who do the same with their sperm, enabling the embryos to be externally fertilised.
Bluefin tuna larvae, like many other fish species, will grow as part of the zooplankton population and will roam the seas at the mercy of currents and ocean upwellings. Once they’ve matured into juvenile tuna, they’ll start schooling with other fish of similar size, including different tuna species in certain cases. Bluefin tuna achieves sexual maturity at around 2–5 years of age, depending on the subpopulation. These fish live for a long time, with some Atlantic bluefin tuna estimated to live for 50 years or more.
Bluefin tuna is a very desirable commercial fishing target. In fact, the Atlantic bluefin tuna fishery may be the most profitable in the world. It’s a highly sought-after species in Japan, where it’s used for sashimi and sushi. It’s also a popular sport fishing area, going back to the 1930s when it was used as a big-game target.
Exploitation and overfishing of the species have happened as a result of this profitable fishery, resulting in a decline of the wild bluefin tuna supply by more than 80% in certain regions of its range. The IUCN Red List of Threatened Species currently lists the Atlantic bluefin tuna as endangered.
Fun Facts about the Bluefin Tuna!
Bluefin tuna is a significant commercial fish and one of the largest fish species on the planet, so there are plenty of entertaining facts and intriguing biological ideas and insights to learn about it.
While tunas are well known for their robust, streamlined bodies and swift swimming speeds, they also possess additional characteristics that contribute to their success as predators. For instance, they hunt only by vision and have superb vision. Indeed, tunas have the sharpest vision of any bony fish species. They can also school with wonderful coordination because to this eyesight.
Hot and Ready
The bluefin tuna, in particular, is a powerful and muscular fish. For propulsion, this power is delivered via a pair of tendons to the tail fin. Tunas’ bodies are stiff, unlike other fish species, and their tails swish back and forth. This decreases drag and improves the effectiveness of each swimming stroke, allowing the tunas to move at such high speeds. These muscles must be kept warm and ready for vigorous usage on demand in order to be responsive when needed.
Tunas are endotherms, or warm-blooded creatures. This enables them to keep their enormous swimming muscles warm, which is necessary for efficient usage. This is accomplished by a process known as countercurrent exchange, in which warm blood in veins distant from the heart is transferred to cooler blood in arteries closer to the heart. The tuna family is made up entirely of endotherms. The bluefin tuna, on the other hand, has a more evolved evolutionary adaptability than other tuna species, enabling them to reach the North Atlantic’s very productive waters.
Don’t Forget the Oxygen
Although it is critical for tuna to maintain their muscles as warm as possible in order to respond swiftly when prey or predators present a threat. However, it is equally critical that their muscles maintain a high level of oxygenation.
In addition to their ability to retain heat, bluefin tunas possess an extremely efficient circulatory system. In fact, it has one of the highest haemoglobin contents in its blood of all fish species. This improved capacity to transport oxygen in its circulation, along with an exceptionally thin blood-water barrier, allows it to keep its tissues at a higher oxygen saturation level than would be possible without these modifications.