Do fish rest? The answer is yes, in the fish tank, we can often see the fish staying somewhere motionless, which is actually resting, but the way the fish rest is different from us, we are continuous sleep, the body can get the maximum rest, but the fish is there time to rest for a while, belongs to intermittent sleep, usually the total amount of sleep a day is only about 2 hours, and because there are no eyelids, the fish is resting with their eyes open.
However, not all fish can rest quietly, some fish have not stopped swimming from birth to death, even when resting, they will maintain a certain speed of swimming, it is the "high-end food" tuna.
Tuna is one of the fastest fish in the ocean, they can reach a maximum speed of 160 kilometers per hour, even when resting, they can maintain a swimming speed of 30 kilometers per hour, if it stops to rest like other fish, then it is likely to die, what is going on? Let's find out together.
What is tuna?
Broadly speaking, tuna is a collective name for all fish under the tuna family of mackerel, there are currently 5 genera and 15 different species, they vary greatly in size, such as the smallest bonito has an average body length of only 35 cm, the largest does not exceed 50 cm, and the largest tuna is Atlantic bluefin tuna, With a maximum length of 4.6 meters and a weight of 684 kilograms, this size of bluefin tuna can be said to be sky-high, because as early as 2019, Japan auctioned a bluefin tuna weighing 278 kilograms, and the final transaction price reached 333.6 million yen (more than 20 million yuan according to the exchange rate with the yuan at that time).
However, tuna in the narrow sense is a member of the tuna family that is often hunted and put in the diet, and there are eight species in total, divided into two categories: bluefin tuna and tuna. There are three types of bluefin tuna: Atlantic, Pacific and Southern bluefin tuna, and there are five species of tuna: long-waisted tuna, albacore tuna, blackfin tuna, bigeye tuna and yellowfin tuna.
In fact, the classification of these tuna is not according to the color of the fins, but according to the color of the fish, bluefin tuna always has a touch on the body, even a blue part, and the name prefix of other species of tuna is actually their characteristics.
Among so many tuna, bluefin tuna is the most expensive, the price of a single catty is thousands, not what we ordinary people can consume, and the price of the other five tuna is relatively low, the tuna fillets we are most commonly exposed to are usually made of bigeye tuna, and canned tuna, usually made of albacore tuna.
In general, the price of tuna in addition to classification, there is also an important reference, that is, their native environment, usually living in colder waters tuna is more expensive, and the higher the temperature of the living sea tuna the cheaper the price, such as the native distribution of bigeye tuna is in the sea near the equator, albacore tuna is mainly distributed in tropical and temperate seas.
Bigeye tuna
Tuna that dies if you don't swim?
Among vertebrates, the most abundant is fish, after all, fish are to some extent the earliest ancestor of all terrestrial vertebrates. Although some fish quietly landed and branched out during the long evolution, most of the fish remained in the water, after all, the widest on earth except the sky is the ocean.
There are currently about 26,687 species of fish named, and this number is increasing at a rate of about 150 species per year, because our human exploration of the ocean is still in its infancy.
Among the known fish, except for hibernation and summer hibernation, fish are usually active, but most fish will intermittently stop swimming every day, which is actually resting. But tuna don't, and they have to swim to hatch from their eggs until they are killed or their lives come to an end. Why is that? There are two main factors:
The breathing mode of fish is divided into two types as a whole: cavity pumping (buccal pumping) and ram ventilation (ram ventilation), of which cavity suction type is the most common breathing method in fish, simply put, through a large mouthful of swallowing water, let the water flow through the gills, thereby absorbing and releasing oxygen and carbon dioxide, almost all bony fish are this breathing method.
And the collision type is that the fish only need to open their mouths, let the water flow into the mouth by themselves, and then flow out of the gills of the fish, complete the gas exchange, this breathing way of the gills are usually gill cracks, that is, cartilaginous fish like sharks, it is precisely because of this breathing method, so that many sharks must also swim all the time to complete the gas exchange, otherwise they will suffocate.
However, tuna is not a way of breathing like sharks, because tuna is a teleost fish, they have their own huge gill covers, so like other teleost fish, it breathes by cavity suction, so why will it die if it does not swim?
This is because tuna and other bony fish cavity suction type is not the same, tuna compared to other bony fish lack a key organ - gill muscle, which is an important muscle group to control their own suction, without this muscle group, tuna has to grow a large mouth like a shark, let the water flow itself into the mouth, and then flow through the gills.
It is precisely because of this that tuna must swim like sharks, so that the current can crash into it and complete breathing, that is, tuna has the same gills as other bony fish, but it cannot breathe like them, can only breathe like sharks, so tuna must swim non-stop from birth, otherwise it will suffocate.
In fact, the gill muscle degradation of tuna is the result of evolution, which is beneficial to them, why say so? Because tuna swims very fast, which makes it need to consume a lot of oxygen, if passively to rely on cavity suction breathing, then the oxygen supplement in the body can not keep up, so when the gill muscle degenerates, the tuna only needs to open its mouth to have a steady stream of oxygen filtered into the body through the gills, which is very efficient.
Such a high oxygen demand, but also tuna body blood is much more than other teleost fish, under normal circumstances, teleost fish blood accounts for between 1.5% and 3%, but tuna blood accounts for up to 20%, blood is obviously more able to transport oxygen. However, this is mutually reinforcing, the needs of the body and the needs of transportation, so tuna must ensure a fast and efficient supply of oxygen, so they must also swim non-stop fast.
Therefore, the difference in respiratory system and the large demand for oxygen make tuna, as a teleost fish, have a breathing method similar to that of cartilaginous fish such as sharks, and it is this breathing method that tuna can no longer stop.
How do tuna rest?
For this animal that has been in constant motion all its life, their sleep was still a mystery until the middle of the last century, and many people even thought that they would not rest, until the 60s of the 20th century, foreign biologists were inspired by the dolphin's "blind eye" state to begin to study how these seemingly moving animals sleep.
Through the research, scientists have found that these animals almost all enter a state where the brain is half resting and half working, which is "half-brain sleep"
When birds migrate long distances, sharks and so on keep swimming, rest relies on semi-brain sleep, tuna is the same, although this sleep mode is not as good as whole brain sleep to the brain rest, but this sleep mode can be they must have, simply put, in order to survive, sacrifice a little rest comfort and time, it is also worth it.
Write at the end
Tuna is an overfished marine fish, although it has been farmed, but the market demand is too large, the main consumption is still wild fishing, it is because of this that some tuna has become a protected animal, such as bigeye tuna is a vulnerable species in the IUCN Red List of Threatened Species.
Therefore, treat a wild fish, do not blindly follow the trend, and what to eat, especially wild resources, should not become a bargaining chip to "show off wealth".