Produced by: Popular Science China
Production: Ye Peiyuan (Shanghai Ocean University, Yunhai Science Team)
Producer: computer network information center
A few days ago, a big news almost swept the circle of friends: Endeavor successfully sat at the bottom of the Mariana Trench, with a depth of 10,909 meters, which is a new depth record for China’s manned submersible!
△ (Source: Chinese Academy of Sciences)
With the continuous development of submersible technology, people have gradually discovered that the vast deep sea is not dead, and countless creatures thrive in this dark place.
Among them,Mariana lionfish, which lives about 8000 meters below the sea surface, is the "deepest deep-sea fish" found by people at present.In contrast, the depth of human diving is generally within 10-20 meters, and the most extreme depth is only 300 meters. You know, at 8000 meters underwater, the hydrostatic pressure is about 800 atmospheres, which is almost equivalent to an adult bull standing on your fingernail. Without the submersible, it is impossible for human beings to reach such a deep sea.
So, how do deep-sea fish bear such great pressure? Is it because they have a good attitude?
Compression resistance, starting from the break of the swim bladder.
Everyone may have an experience when swimming: when you dive into the bottom of the swimming pool, you will feel a sense of oppression in the eardrum, even a slight pain. This is because the water pressure outside the eardrum is obviously greater than the air pressure inside, resulting in an inward pressure on the eardrum. From this example, we can draw a conclusion:With the increase of water depth, the water pressure will be much higher than atmospheric pressure, causing the surrounding water to start squeezing the inflated objects inward.
△ (Source: Pexels)
Most bony fish are an inflatable object in a sense, because they have an inflatable swim bladder in their bodies. For bony fishes living in shallow water, the swim bladder is a very important structure, which can help fish adjust their buoyancy, so as to float or dive. But for deep-sea fish, the air-filled swim bladder is just like a fragile balloon, and the huge external water pressure will squeeze and trample the balloon without reservation until it is blown to pieces. Therefore, many deep-sea fish "abandoned" the "dangerous" structure of swim bladder in the process of evolution, and instead relied on some lipids to provide buoyancy.
Compared with fish in shallow water, deep-sea fish have less bones and muscles, but more lipids and gums. In addition, the proportion of cartilage in the bones of deep-sea fish is much higher than that of shallow-sea fish.For deep-sea fish, this is a necessary "compromise" to adapt to deep-sea life. As the saying goes, "rigidity is easy to break", compared with bones and muscles, lipids and gums can better help fish resist great pressure.
At the same time, this body structure has another advantage.Low proportion of bones and muscles can reduce the energy consumption of deep-sea fish, while high proportion of lipids can store more energy at the same time, which is very important for fish in the deep sea with poor nutrition and thin oxygen.
A few years ago, it was rated as the ugliest creature in the world, and the water-dripping fish-the soft-hidden echinoderma is a good example. The water-dripping fish caught ashore is often a pool of soft pink objects, lifelike like a slime with a big nose. However, in the deep sea, the shape of water-dripping fish is no different from that of ordinary fish, but in the process of being caught ashore, their body structure is destroyed due to the rapid reduction of pressure, which has become what we see. In the place where they live, it is this colloid that helps them survive.
△ Dropfish (Source: Wikipedia)
Previous studies have found that in the genome of Mariana lionfish, genes regulating bone development and bone tissue ossification have mutated. This mutation will lead to the early termination of the calcification process of Mariana lionfish bones, resulting in most of its bone components being cartilage. The ability of cartilage to resist high pressure is far stronger than that of hard bone tissue.
△ Molecular mechanism of special phenotype of Mariana deep-sea lionfish (Source: Reference 1)
Deep into the cell membrane, strong compression resistance
However, this is not all the skills of deep-sea fish.
You know, hydrostatic pressure is not a macroscopic object, it is not like a hand holding a deep-sea fish tightly, and it will only affect the deep-sea fish from the macroscopic body structure.Hydrostatic pressure is pervasive, and it will attack both macro structure and micro structure.
When we focus on the microscopic world, we will find that the fluidity of cell membrane will decrease under high pressure. Simply put,In the deep sea, the cell membrane will become more "hard".This is not a good thing. Cell membrane is an important gateway to control substances entering and leaving cells, and hardening of cell membrane will make it more difficult for substances to enter and leave cells. The nutrients outside the cell can’t enter the cell, and the waste produced in the cell is difficult to be transported out of the cell, so the creature will not survive. It’s like a takeaway who wants to deliver a takeaway through a crowded intersection: originally, he just had to squeeze through the cracks, but as a result, a mysterious force pushed everyone together, making everyone stick to everyone, and the takeaway couldn’t squeeze through despite his desperate efforts. At this time, he would feel great pressure.
Scientists have found that,Compared with shallow-sea fish, deep-sea fish have more unsaturated fatty acids on their cell membranes, which enables their cell membranes to maintain a high level of fluidity under high pressure and improve the efficiency of material transportation.
For example, vegetable oil has a higher content of unsaturated fatty acids than animal oil, so vegetable oil is generally liquid at room temperature, while animal oil is mostly solid. It is difficult for you to let a coin penetrate a piece of butter, but it is easy to let it fall from the surface of a bottle of peanut oil to the bottom of the bottle.
A high proportion of unsaturated fatty acids can make deep-sea fish have a "soft" cell membrane even in a high-pressure environment. However, if a deep-sea fish is caught ashore, its cell structure will also be destroyed, because when it is in a low-pressure environment, the cell membrane is a little too fluid and too "soft", which leads to cell breakage.
△ Analysis of 9 teleost gene families showed that the gene families related to fatty acid metabolism in MHS were significantly amplified (image source: Reference 1).
Lipids are not the only substances affected by high pressure, and it is difficult for protein to escape the ubiquitous pressure.Normally, the structure of protein affected by high pressure will change and its function will lose, and the normal work of protein is very important for the survival of living things.
Fortunately, deep-sea fish also have corresponding coping strategies for this.The amino acids in some protein-specific sites of deep-sea fish will be replaced by other amino acids, which will improve their resistance to stress.For example, α -actin in deep-sea fish has been substituted by amino acids at many sites, including the binding site of calcium ion and ATP. Amino acid substitution at these two sites can ensure that actin can still work normally in high pressure environment.
In addition, the number and types of chemical bonds in some protein will change to some extent.This change leads to the change of protein tertiary structure, thus strengthening the rigidity of protein structure and improving its adaptability to high pressure environment. Just like when you put two more tapes on the outside of a building block, it is definitely much more stable than not putting tape on it.
It has also been found that the content of trimethylamine oxide (TMAO) in deep-sea fish is much higher than that in shallow-sea fish. Trimethylamine oxide is a very important protein stabilizer, which can help denatured protein to recover its original structure, thus restoring its normal function.A large amount of trimethylamine oxide in deep-sea fish can help the protein in their cells to maintain the original structure and function, thus ensuring the cell activity.
Interestingly, with the death of fish, trimethylamine oxide will gradually decompose into trimethylamine, which is an important source of fishy smell of marine fish. That is to say, the more deep-sea fish, the heavier the smell after death, and it is not difficult for inland friends to understand that hairtail always has a heavy smell.
△ These changes in gene coding and regulatory sequences may help MHS increase intracellular TMAO level to enhance protein stability (image source: Reference 1).
Nowadays, some people always feel that the surrounding environment has put a lot of pressure on them, and they choose to live in Buddhism or even give up on themselves. But think about it, the fish in the deep sea have not given up under such great pressure. Even if they start to change themselves from the protein level, they should adapt to the environment and become the masters of the environment. What reason do you have to give up? Take action to change yourself and overcome the pressure!
Team Introduction: Yunhai Science Popularization Team is an interesting science popularization team from China Ocean University. It deconstructs seemingly profound scientific problems from the unique perspective of young people, and makes you discover that nature is so interesting.
References:
1、Morphology and genome of a snailfish from the Mariana Trench provide insights into deep-sea adaptation![[J]](https://baidubox-emoji.cdn.bcebos.com/imgs/%5BJ%5D.png?r=2025100816 "[J]")
. Nature Ecology & Evolution, 2019.
. Nature Ecology & Evolution, 2019.2、Cocker J E . Adaptations of deep sea fishes. Environmental Biology of Fishes, 1978, 3(4):389-399.
. Environmental Biology of Fishes, 1978, 3(4):389-399.3、Haedrich R L . Deep-water fishes: evolution and adaptation in the earth’s largest living spaces. Journal of Fish Biology, 2010, 49(sA):40-53.
. Journal of Fish Biology, 2010, 49(sA):40-53.4、Morita T . High-pressure adaptation of muscle proteins from deep-sea fishes, Coryphaenoides yaquinae and C. armatus. Annals of the New York Academy of ences, 2010, 1189:91-94.
. Annals of the New York Academy of ences, 2010, 1189:91-94.5、Winnikoff J R , Wilson T M , Thuesen E V , et al. Enzymes feel the squeeze: Biochemical adaptation to pressure in the deep sea. Biochemist, 2017, 39(6):26-29.
. Biochemist, 2017, 39(6):26-29. 6、Robert Kunzig. The Physics of . . . Deep-sea Animals，Discover，2001
Reporting/feedback
关于作者