Why are the fish in the deep sea not crushed to death by the pressure of water?

We all know that with the depth of the water, the pressure will get bigger and bigger. The more people dive into the water, the greater the water pressure will be. In the general pressure of the atmosphere, nitrogen is not dissolved in the blood, when the pressure reaches 3 atmospheres nitrogen can be dissolved in the blood, if the stronger the pressure, the solubility will gradually rise a lot. 100 meters underwater position, the blood may be dissolved in a large amount of nitrogen, and the body needs a lack of oxygen. Eventually, nitrogen involuntarily runs out from the blood and is blocked in the blood vessels, and eventually may let the blood vessels rupture, if the rupture occurs in the body's important blood vessels, people will die directly.

It is difficult for humans to enter 100 meters, how can the deep-sea fish in the sea survive it?

Deep sea, deep sea, that how deep is considered deep sea? International more than 1,000 meters depth of the sea is called the deep sea, according to the liquid pressure formula p = density × g × depth (roughly the seawater as water) to get the deep sea 1000 meters of pressure equivalent to 100 times the atmospheric pressure.

What is this concept, a basketball-sized object can be squeezed into a ping-pong ball size?

Adaptation of deep-sea fish

Fish in the deep sea by the pressure is not completely balanced inside and outside and offset, oceanographers sink a plastic cup with the detector into the deep sea, we can see the above picture on the left is intact cup; the right is immersed in the deep sea 1500 meters cup, the cup has been completely flattened, the cup inside and outside is indeed balanced inside and outside pressure, balanced at all depths of the sea floor, but also failed to offset the pressure, because as long as there is a solid form will be compressed by high pressure.

The fish living in the deep sea have evolved by natural selection a new internal structure to counteract this high pressure, evolving at the molecular and cellular level to counteract the high-pressure environment. The small size of proteins in deep-sea fish and the catalytic efficiency of enzymes are much less than those of fish in shallow waters, and these characteristics are the primary conditions for survival in high-pressure environments. We can understand that since the seawater wants to oppress me, I will first make my structure smaller to reduce the pressure of the seawater.

Compared with fish in shallow waters, deep-sea fish have less skeletal and muscle content, while relatively more lipids and gums. In addition, the proportion of cartilage in the bones of deep-sea fish is also much higher than that of shallow-sea fish. For deep-sea fish, this is to adapt to the deep sea life made necessary "compromise". The so-called "too rigid is easy to break", compared to the skeleton and muscle, lipid and gelatin can better help fish to fight against the huge pressure.

In addition, deep-sea fish adapt to the environment, in the cell membrane and other biological membrane phospholipids become more mobile, because if their cell membrane is too rigid, it will form a confrontation with the water pressure, and the biological channels in the cell membrane will be closed, the normal physiological function will be affected. Compared with fish in shallow waters, most fish in deep waters use unsaturated fatty acids to form their cell structure, which greatly increases the fluidity of the membrane.

The lower proportion of bones and muscles reduces the energy consumption of deep-sea fish, while the higher proportion of lipids can store more energy at the same time, which is essential for fish in nutrient-poor, oxygen-poor deep waters.

In terms of organs, most deep-sea fish do not have swimbladders, such as sharks. Because of the presence of the swim bladder the internal gas is directly impacted by the water pressure, just like humans diving into the deep sea. If deep-sea fish enter shallow waters, then the cells in the deep-sea fish feel the environment with less pressure, and because the cell membrane is very fluid, then the substances that build the cells will seep out of the cells, and the fish will not die immediately, but the important nervous system will be damaged and become an "idiot".

Most scleractinian fish are in a sense inflatable objects because they have an inflated swim bladder inside. For bony fish living in shallow waters, the swim bladder is a very important structure that helps fish adjust their buoyancy so that they can float or dive. But for deep-sea fish, an air-filled swim bladder is like a fragile balloon, and the enormous external water pressure will squeeze and ravage the balloon without reservation until it blows to pieces. Therefore, much deep-sea fish have evolved to "abandon" the swim bladder as a "dangerous" structure, relying instead on certain lipids to provide buoyancy.

Compared to fish in shallow waters, deep-sea fish have less bone and muscle and more lipids and gums. In addition, the proportion of cartilage in the bones of deep-sea fish is also much higher than that of shallow-sea fish. For deep-sea fish, this is to adapt to the deep sea life made necessary "compromise". As the saying goes, "too rigid is easy to break", compared to the skeleton and muscle, lipid and gelatin can better help fish against enormous pressure.

Such a body structure has another advantage: a lower proportion of bones and muscles can reduce the energy consumption of deep-sea fish, while a higher proportion of lipids can simultaneously store more energy, which is essential for fish in the nutrient-poor, oxygen-poor deep sea.

A good example of this is the soft-spined sculpin, which was named the world's ugliest creature some years ago. Caught ashore, the sculpin is often a floppy pink mess, resembling a slime with a big nose. However, in the deep sea drip fish's appearance and ordinary fish are not the same, only in the process of being caught ashore, due to the rapid reduction in pressure so that their body structure is destroyed, into the appearance we see. And where they live, it is this gelatinous body that helps them survive.

Previous studies have found mutations in the genome of Mariana's lionfish in genes that regulate skeletal development and ossification of bone tissue. This mutation causes the calcification process of the Mariana lionfish skeleton to terminate prematurely, resulting in a majority of cartilage in its skeletal composition. Cartilage is far more resistant to high pressure than hard bone tissue.

However, these are not all the skills of deep-sea fish.

It is important to know that hydrostatic pressure is not a macroscopic object, it is not like a hand that squeezes the deep-sea fish dead, only from the macroscopic body structure of the deep-sea fish. Hydrostatic pressure is pervasive, and both macroscopic and microscopic structures are attacked by it.

When we gather our eyes to the microscopic world, we will find that the mobility of cell membranes decreases under a high-pressure environment. Simply put, the cell membranes of cells in the deep ocean become more "rigid," which is never a good thing. The cell membrane is an important gate that controls the flow of substances in and out of the cell, and a stiffer membrane makes it more difficult for substances to enter and exit the cell. Nutrients from outside the cell will not be able to enter the cell, and waste products produced inside the cell will not be able to leave the cell, so the organism will not be able to survive. This is like a delivery man going through a crowded intersection to deliver: originally he just had to squeeze through the cracks, but then there was a mysterious force pushing everyone towards one piece so that people were crowded, and the delivery man tried his best to squeeze through, and then he would feel so much pressure.

Scientists found that, relative to shallow sea fish, deep-sea fish have more unsaturated fatty acids on their cell membranes, which allows their cell membranes to maintain a higher level of fluidity in high-pressure environments and improve the efficiency of material transport.

To use an analogy, vegetable oils have a higher content of unsaturated fatty acids compared to animal oils, so at room temperature, vegetable oils are generally liquid, while animal oils are mostly solid. You'd be hard-pressed to get a coin to penetrate a piece of butter, whereas it's easy to get it to fall from the surface of a bottle of peanut oil to the bottom of the bottle.

The high percentage of unsaturated fatty acids allows deep-sea fish to have "soft" cell membranes even in high-pressure environments, but if a deep-sea fish is caught and landed, its cell structure will be destroyed because when it is in a low-pressure environment, the cell membranes are somewhat too fluid, and the cell membranes are too " soft", causing the cell to break down easily.

Lipids are not the only substances affected by high pressure, but proteins also have difficulty escaping this ubiquitous pressure. Normally, proteins affected by high pressure will undergo structural changes and loss of function, and the proper functioning of proteins is essential for the survival of living things.

Fortunately, deep-sea fish have strategies to cope with this. In deep-sea fish, certain amino acids at specific protein sites are replaced by other amino acids, increasing their resistance to stress. For example, alpha-actin in deep-sea fish undergoes amino acid substitutions at several sites, including the binding sites for calcium ions and ATP. Amino acid substitutions at these two sites ensure that actin can still function properly under high-pressure environments.

In addition, some proteins undergo certain changes in the number and type of chemical bonds. This change leads to a change in the tertiary structure of the protein, which strengthens the rigidity of the protein structure and thus improves its adaptability to high-pressure environments. It's like when you put two extra pieces of tape on the outside of a block when building it, it's much more stable than if you don't put any tape.

It has also been found that the level of trimethylamine oxide (TMAO) in deep-sea fish is much higher than in shallow-sea fish. Trimethylamine oxide is a very important protein stabilizer, it can help the denatured protein to restore its original structure, and thus restore its normal function. A large amount of trimethylamine oxide in deep-sea fish can help the proteins in their cells to maintain their original structure and function, thus ensuring cellular activity.

Interestingly, as fish die, oxidized trimethylamine will gradually break down into trimethylamine, which is an important source of the fishy smell of marine fish. That is to say, then, the deeper the fish, the heavier the fishy smell after death.