do you know tuna ? This migratory fish, which mainly inhabits tropical and subtropical areas, has an incredible special physiological characteristic: From birth, tuna must swim non-stop to maintain the normal operation of vital signs. Only death can make them truly Stop.
So, what kind of fish is tuna? What kind of biological evolution principles does behind swimming all your life?
What is tuna?
I believe everyone is familiar with the name tuna. They have a nearly standard streamlined body and can move flexibly and quickly in seawater. From the perspective of species distribution, tuna likes warm aquatic environments. my country's East China Sea and South China Sea are suitable habitats for this fish. Even if we have never seen wild tuna, we can still find them in major aquariums or in the underwater world.
Of course, there is another way to get familiar with tuna, which is at the table . Because tuna meat is delicious and rich in protein and other nutrients, many places around the world have a dietary tradition of eating tuna. For example, the famous tuna sashimi in Japanese cuisine, the tender fish meat is mouth-watering.
At the same time, tuna is also a large marine carnivorous fish. The largest species - Atlantic bluefin tuna can reach four and a half meters in length and weighs nearly 700 kilograms. You know, an adult male Siberian tiger can grow to more than two meters long and weigh up to 250 kilograms. In other words, in front of the Atlantic bluefin tuna, even though it is the "King of the Forest" on land, it can only be described as "petite and thin".
Even if we use marine animals that are independent of terrestrial ecology for comparison, the currently largest known octopus is only about two meters in size, and the recognized marine food chain "ceiling" - the great white shark, has an adult fish length of no more than 2 meters. Six meters. Looking at the entire ocean, large tuna can be regarded as advanced predators.
However, not all tuna are as big as their big brother. Among all the fifteen species of tuna, there are also small species such as and bonito , which are less than fifty centimeters in length. It can be seen that although they are a type of carnivorous fish that hunt other life, they are also a species that differs greatly within the same category.
This also shows that tuna is actually a creature with relatively backward evolution. The problem of is easy to understand. Not to mention the most advanced humans, even lions, tigers, orangutans and other mammals, there are no obvious differences in appearance between various "relatives" in the same category. For example, there is basically no difference between North African lion and the South African lion commonly seen in documentaries.
Tuna's backwardness in the evolution of respiratory organs
means that tuna as a species must bear some pressure from nature. The defect of 's respiratory organs, , which causes them to swim in the water all the time, is a concrete manifestation of this problem.
First of all, we must make it clear that fish also needs to breathe . Many people think that since fish live in water, if they can still breathe, wouldn't it be a self-destructive contradiction?
In fact, this is not the case. All animals on the earth, including various fish, rely on oxygen to provide life activities. Simply put, it allows oxygen to enter the body, promote blood circulation, and maintain vital signs.
Moreover, water is also with oxygen. This air comes from many places. For example, the atmosphere discharges some gases into the water through atmospheric pressure. In addition, plants in the water can also perform photosynthesis to produce oxygen like land plants. However, the oxygen content in the water is much lower than on land, so if fish want to survive here, respiration is a very important behavior.
Under normal circumstances, fish will evolve gills on both sides as their unique respiratory organs , with various blood vessels covering the gills.When fish need to inhale oxygen, their gills will expand and open, exposing blood vessels to directly absorb oxygen from the water and then supply it to all parts of the body.
This is the basic principle of fish breathing.
However, the above situation also requires specific analysis. From the perspective of bone quality, there are two types of fish on the earth - bony fish and cartilaginous fish . Among them, bony fish have strong skeletal support and can freely control the activities of various organs like many animals on the ground. Cartilaginous fish like tuna have to make up for this lack in evolution through more effort in action.
Tuna also have gills, which also need gills to inhale oxygen, but because their bones are cartilage, it is difficult to fully open the gills in a static state. In other words, if the tuna just allows the body to breathe motionlessly, it can be understood conversely as us humans gasping for air while running. Although they can also inhale some oxygen, the content of this oxygen cannot support life activities for a long time. .
Therefore, tuna have to keep swimming in order to survive. Only in this way can the gills be fully expanded by the power of the body, thereby ensuring that sufficient oxygen supply is always available.
So, tuna doesn’t even have time to sleep and rest, does it have to swim all the time?
The answer is yes, but that doesn't mean the tuna won't rest. A living organism is not a machine. Although it operates according to certain rules, it is impossible not to rest and adjust. This is true even for tuna that swims from birth to death. According to relevant research, during their daily activities during the day, tuna, in addition to suddenly attacking prey, will also move at a specific speed and at a constant speed; when they rest at night, they will swim at a low speed and continue to breathe. .
The evolution of tuna
In this way, do you feel sorry for these "footless birds" in the sea? Even the so-called rest is just swimming a little slower than usual, and the whole life is dedicated to this endless ocean.
However, the "footless bird" that can only fly and cannot stop since birth is just a fictitious animal, and its image of hard work or misery is just people's romantic imagination. In reality, the biological characteristic of tuna that needs to keep swimming is an evolutionary necessity of natural selection.
We mentioned at the beginning of the article that tuna can have a streamlined body shape and flexible movement because of the cartilage structure in its body. Without these, they would not have such efficient swimming ability, and they would become Without the predators in the ocean, they can only be clumsy prey.
So, existence is reasonable, this is the principle of nature. Although biologically speaking, the evolutionary level of tuna can only be regarded as a relatively low-level stage, but on this blue planet, there are no backward life forms, only backward ways of survival. As long as can ensure the survival of the species, then the cost of giving up any body part is worth it.
In addition to tuna, there are many similar biological cases.
For example, and the Madagascar blind snake , in order to acquire the outstanding ability of smell to hunt prey, they gave up the evolution of vision and were willing to become "eyeless snakes".
There are also sloths that play cute roles in many animated film and television works. Due to their slow movement, it is often difficult for them to escape when faced with the harassment of natural enemies.
However, this also alleviates the rapid digestion of food energy in the body, so that activities exposed to the outside can be avoided as much as possible, and the possibility of encountering natural enemies is fundamentally reduced.
Whether it is tuna, Madagascar blind snakes, sloths or all such animals that "save one thing for the other", in their long evolutionary process, only the destruction of nature by humans is their biggest survival threat. Take tuna, for example. Of the fifteen categories mentioned above, seven are already listed as endangered.The reason for this is obvious. No matter how fast the tuna moves, it cannot match human-powered ships; no matter how many physiological characteristics it abandons, it cannot adapt to sea water polluted by human activities.
Therefore, protecting the ecological environment and global flora and fauna is still a serious issue that we must face. Only the harmonious coexistence of all things is the greatest significance of the existence of this planet.
Author: Kinoshita Yiren Proofreading Editor: Xiaowan
