Back in 2019, a bluefin tuna of about 555 catties was sold for $3 million at Toyosu Market in Tokyo, Japan. What is the origin of this tuna? What are the stories of the rise and fall of its family?
Different tuna vary greatly depending on the species, size, fertility, conservation status, etc.
The appearance of all beings in the tuna family
Tuna is a special and important presence in the global marine fishing industry. The mackerel (qīng) family, where tuna is located, supports the pelagic tuna fishery including longline, tuna purse seine and other fishing methods, and a total of 7.8 million tons of mackerel** are caught in the world every year, bringing tens of millions of dollars in huge profits to countries around the world.
One-size-fits-all. But for most ordinary people, tuna is often an unfamiliar concept, except for the tuna sashimi on the menu of Japanese restaurants and the neatly stacked canned tuna in supermarkets. In fact, these fishery economic species, which are of great significance to human beings, also play an important role in the marine ecosystem.
Tuna in a broad sense includes tuna and tuna-like (other mackerel-like fishes), of which the latter includes bonito (jiān), ba's bonito, rudder bonito, fox bonito, mackerel, etc., and many of the canned tuna we buy in supermarkets are made from tuna-like fish. And tuna in the narrow sense refers specifically to the 8 species of the genus Tuna:
Yellowfin tuna.
Bigeye tuna.
Northern bluefin tuna.
Oriental bluefin tuna.
Southern bluefin tuna.
Albacore tuna.
Green dried tuna.
Blackfin tuna.
Different species of tuna vary greatly in size, with the largest northern bluefin tuna growing up to 458m, weight up to 684kg; The smallest blackfin tuna has a maximum body length of only 108m and weighs up to 20kg.
The northern bluefin tuna, one of the most famous large fish species, was displayed at the Qingdao International Fish and Fisheries Expo in China. Photo: Luo Lan.
In terms of species alone, the genus tuna, consisting of only eight species, is not worth mentioning in the huge class of radial-finned fish, but they play an irreplaceable role in the global marine fishing industry.
Tuna has a long history with humans, and here is an ancient Greek gold coin engraved with the image of a tuna and a dolphin. ©7k today
After nearly 10 million years of evolution, today's tuna has adapted to the fast swimming life of open water, with many characteristics, these ferocious predatory fish have expanded their territory to the tropical, ** zone and warm temperate open sea area on a global scale, can be described as one of the most successful oceanic fish.
If you stop swimming, you will suffocate
According to the different swimming styles, the swimming patterns of living fish can be roughly divided into four categories: eel swimming, trout swimming, trevally (shēn) swimming and tuna swimming (wěi).
After all, among all the existing fish, tuna swimming can only be regarded as a "niche genre", and the torso of the fish used is relatively stiff, and the central axis of the trunk is always horizontal when swimming, relying on the left and right swing of the tail to achieve rapid movement.
Schematic diagram of the four swimming modes of fish, from left to right: eel, trout, trevally and tuna. Source: valentinadisanto
Although trout swimmers are much more efficient than the previous "mass" strokes, they are also the least stable of the four. This has become a common problem for tuna and all fast-swimming fish, but life will always find its own way out, and tuna is naturally the same.
If you want to swim fast and reduce the impact of drag as much as possible, you can do it in two ways: reduce your own drag and increase your wake, and tuna can do both.
Tuna'sThe torso evolved into a standard streamlined shapeThe fat trunk with a slender tail allows the trunk to balance the lateral force generated by the large swing of the tail peduncle while swimming at high speed.
Secondly,The grooves at the base of the pectoral fin, pelvic fin, and first dorsal fin allow the fins to be retracted and released freelyto minimize drag.
In addition to the scales of the chest to form a strong cuirass to protect the internal organs,The scales of tuna are small round scales buried under the skin, which takes it to the next level in terms of reducing drag.
To further increase the wake, tunaEvolved caudal peduncle lateral process, which provides an attachment point for the well-developed caudal peduncle muscles, and also grows the caudal peduncle. At the same time, the cross-section of the tail peduncle is approximately diamond-shaped, like an axe splitting the water flow, thereby reducing the water flow resistance of the tail.
dorsal and anal fins behind themThe free fins act as "spoilers."to further enhance the stability of the tuna's swimming.
The well-developed caudal peduncle lateral process and free small fin are important "secrets" for the high-speed movement of tuna.
Of course, as an athletic athlete in the ocean, tuna's muscles, like most fast-swimming fish, are dominated by myoglobin-rich red muscle. Compared to white muscles, red muscles are less explosive but have excellent persistence, and these muscles are enough to support tuna for ultra-long migrations. The white muscles of tuna are mostly distributed on the periphery of red muscles, so as to ensure the instantaneous explosive power of marlin when preying and avoiding predators.
The muscles of tuna are mainly myoglobin-rich red muscles. Source:
With this equipment, the tuna can reach a top speed of 74 km/h, which is on par with the fastest ungulates on land, the pronghorned antelope, a speed that makes the tuna almost invincible in the ocean, after all, most predators simply can't catch up with it.
Tuna adopted ".Ram breathing"Trapping dissolved oxygen in water. As they swim, they simply open their mouths and let oxygen-laden water pass through their gill filaments to complete the gas exchange process. This breathing style is undoubtedly suitable for the high-speed swimming upper class, but it has also become the "Achilles' heel" of tuna - once they stop swimming, they will suffocate to death because they cannot take in large amounts of oxygen in time.
It is possible to dive and swim far
As a surface fish, tuna also has excellent diving capabilities, among which bigeye tuna can reach a maximum depth of 1500m; The tuna's adaptability to water temperature is far beyond our expectations, and even in the temperate waters of high latitudes, where the water temperature is only 3, the northern bluefin tuna can still move freely.
Much of this has to do with the tuna's special circulatory system, which relies on a circulatory network called a "strange net" that keeps the local blood temperature higher than the ambient water temperature, thus ensuring that it can maintain mobility in cold water. This characteristic allows fishermen to remove the internal organs and gills of tuna immediately after catching it and freeze it quickly to prevent meat decay caused by local body temperature overheating.
Frozen tuna.
As one of the most well-known migratory fish, tuna also has an excellent ability to migrate long distances. Tuna can swim up to a staggering 230km a day; An oriental bluefin tuna can travel 3 times between the Pacific Ocean in 600 days, with a total distance of 40,000km, which is equivalent to circumnavigating the world along the equator! This ability to migrate long distances is difficult for most fish species to match. The "street runner" nature of tuna has also made the management of fisheries for this species a global issue.
Apex predator in the open sea
Tuna are voracious predatory fish and are preferred prey by small and medium-sized fish, molluscs and crustaceans that are active in surface and mid-water waters. In order to prevent small prey from escaping from the gills, tuna evolved well-developed gill rakers, thus ensuring efficiency when hunting.
The stomach contents of an oriental bluefin tuna are mainly composed of pelagic fish and cephalopods.
Tuna can eat up to 18% of its body weight at a time, apparently in response to its high-consumption fast-swimming. Tuna also follow their prey in a vertical migration: diving into the midzone during the day to feed, and rising to the surface at night.
Yellowfin tuna, which preys on small fish in surface waters.
Several species of large tuna have trophic levels in the range of 4-4Between 5, and almost equal to some of the larger sharks, these fast-moving hunters are undoubtedly apex predators in the open sea.
Of course, tuna is not invincible in the ocean. Marlin, swordfish and large sharks such as barramundi and blue sharks are very fond of preying on tuna, and large toothed whales such as false killer whales occasionally hunt tuna. Some of the smartest, large, toothed whales will even follow the longline vessels and feast on the hooked tuna.
Indian Marlin: That's what you call it!
Nature's "Yusheng winners".
During the breeding season, schools of tuna mate in the upper waters. The eggs of tuna are floating eggs that float in the surface sea by oil balls. In dangerous surface waters, tuna eggs hatch for a short period of time to prevent unsuspecting eggs from becoming food for other organisms.
In the case of yellowfin tuna, for example, the fertilized eggs can hatch in 24-36 hours when the water temperature is 26. Despite this, there are still a large number of eggs and pheasant larvae that are sacrificed during the growth process, but for tuna that employ "fish-sea tactics", there will always be a significant number of individuals who survive to adulthood out of the millions of eggs laid by each female. As long as they survive to adulthood, the tuna can rest easy, as only a few predators can threaten them.
The development of juvenile to juvenile yellowfin tuna.
Tuna have a long lifespan, and the largest of them, the northern bluefin tuna, can live up to 35 years, which is considered a high lifespan among fish. There is no doubt that in nature, tuna can be considered a "fish winner", but since the day humans set foot in the ocean, everything has begun to take a turn...
Victims of overfishing
As early as the Neolithic period, the ancestors of the East Asian coast began to hunt tuna. However, because tuna is extremely perishable, it was once regarded as an inferior food fish in ancient times when storage and transportation technology was backward.
It was not until the innovation of freezing and preservation technology after World War II that tuna ushered in the "dawn" and became one of the most important global economic fishes. Tuna has become a "cash fish" for many coastal countries, contributing to the global economy and providing a large number of employment opportunities.
A large amount of tuna waiting to be auctioned at the Toyosu market in Japan.
But at the same time, growing overfishing has created an unprecedented crisis for tuna stocks. According to incomplete statistics, at least 41% of the world's tuna stocks may be overfished, and two species of bluefin tuna were even endangered at one point due to intensive fishing.
As an apex predator in open waters, a significant reduction in tuna populations is bound to have an impact on the balance of the ocean. At the same time, tuna fisheries, such as longlines and tuna purse seine nets, have also been criticized for the bycatch of sharks, turtles, seabirds and cetaceans due to the production process.
A whale shark that is caught by purse seine operations targeting tuna and bonito.
In addition, as an apex predator, tuna is often the "hardest hit area" for heavy metals such as lead and mercury, which accumulate in large quantities along the food chain and eventually affect tuna eaters.
For the elderly, infants and young children, the toxic effects of bioaccumulation are more significant, so these groups should avoid tuna products as much as possible. Some businesses like to add tuna meat to baby food, which is undoubtedly extremely irresponsible.
Artificial breeding brings the light of day
Fortunately, countries around the world have recognized the grim situation of the sharp decline in tuna stocks, and have begun to carry out effective measures for the conservation of tuna resources, such as strengthening resource investigation and assessment, formulating reasonable resource conservation plans, implementing quota fishing, and cracking down on illegal fishing.
Fishermen are using purse seine nets to catch northern bluefin tuna.
At the same time, fishermen are also working hard to overcome the difficulties of tuna farming. In 2002, the University of (Jī) in Japan successfully achieved the full artificial breeding of oriental bluefin tuna. Although the volume of output is still not enough to fill the huge consumer market, it at least gives us hope. Compared with wild tuna, farmed tuna has a higher fat content and a more creamy taste, and in the near future, farmed tuna is expected to replace wild tuna to a certain extent, which is undoubtedly of great significance for the protection of wild tuna populations.
Oriental bluefin tuna, which was cultivated at University, is now in the stage of mature commercial production.
The hard work paid off, with the IUCN downgrading five tuna species in September 2021 and the problem of bycatch caused by the tuna fishery eased. There is no conflict between the protection and development of tuna resources, and the key is to strike a balance between the two in order to achieve sustainable development of tuna fisheries.
Yellowfin tuna is currently the most caught tuna in the world.
There is no doubt that tuna's pursuit of speed has made this evolutionary "work of art", and the exploitation of tuna fisheries and the conservation of their resources have created an inseparable link between them and humans. The legend of tuna is far from over, and the stories of these "ocean rangers" will continue to ......be written by them