Fish is a very interesting animal.
Of course, not because the fish meat is so delicious, but simply because it really contains many mysteries.
Most people have seen fish pecking. With a kitchen knife and then carefully pulling out its internal organs, you’ll see a large white and slightly transparent wrap, called a fish bubble.
In many books, articles or even the teachings of parents and teachers, many people believe that bubbles are the organ used by fish to control the climb and dive. The description is basically fish controlling buoyancy by varying the volume of the bubbles, in order to control buoyancy and diving in the water.
Basically, that is also the principle of the submarine’s operation. Because the magnitude of the buoyancy is related to the volume of water an object takes its place. According to Archimedes’ principle, an object immersed in a fluid receives a repulsion equal to the weight of the fluid displaced by it.
The famous story of playing with water while taking a bath of Argentina.
And if you ever looked at the bubbles that were taken out of the fish’s belly, you might notice they were soft and elastic, like a balloon. It seems that fish using it to control floating and diving is justified.
Everyone even thought that way from over 300 years ago. This theory was first discussed by professors at the Academy of Sciences in Florence, Italy, and finally formally formulated by Professor Porrelli in 1685. This detailed statement is consistent with common sense. Ours is a fish that enlarges a bubble to float and compresses it to dive.
But, this theory has one serious flaws. That is, it proposes that the fish actively control the size of the bubbles in order to change buoyancy, without explaining how the fish controls.
Close-up of fish bubbles.
Today, when dissecting a fish bubble, we can see that its structure is divided into three layers. The outer layer is fibrous tissue, tough and transparent, containing guanin crystals and airtight. The middle layer is the connective tissue of collagen fibers and is elastic. The innermost layer is the epithelial cell containing only a few blood vessels.
It can be seen that the entire fish bladder is completely devoid of muscle tissue. Therefore, the fish cannot actively change the size of the bubbles. At this point, another hypothesis arises: Can the fish inflate and deflate the bubbles through other organs?
This can be verified through simple life experiences. When we peck the fish on our own or watch someone else peck the fish, it’s easy to see that the bubbles removed from the fish’s belly are not only intact, but won’t even leak out the air. It only flattens after it is cooked. This suggests that the bubbles in many freshwater fish species do not have the pipes to push or release the air quickly.
Fish bubbles are very airtight and difficult to collapse even for a long time.
In fact, fish bubbles are divided into two parts, knotted in the middle. The anterior part is smaller, connecting with the digestive tract. Some fish can actually breathe through a bubble, but at a very slow rate. According to calculations, it took 4 hours to artificially fill the salmon bubbles, this speed clearly could not meet their need for continuous floating and diving.
Another problem that also undermines the popular notion about fish bubbles is that according to the classical theory, fish need to add air to the bubbles when floating and expel them during diving. In practice, however, fish cannot breathe air in the water and will not release air bubbles when diving.
A popular concept about the function of a fish bubble.
What is more difficult to explain is that when a fish dies, many freshwater fish will raise their bellies and float to the surface. This is not the same as rotting and producing gas in a normal animal’s body after drowning.
In some illegal fishing activities, such as electric stings or poisoning, these methods can kill fish in a short or even instant. So how do these dead fish control and change the volume of the bubbles to float on the surface of the water?
The submarine, thought to be designed to mimic fish, will not automatically rise to the surface of the ocean after a shot or power failure, but can only sink. Obviously, the principle of submarine floating and diving is not based on the bubble-like behavior of the fish in the environment.
Dead fish often float to the surface of the water.
Over the past 300 years, the argument that fish control bubbles for swimming has been written into many textbooks and has almost become a common life experience.
But science has gradually revealed shortcomings in this theory. For example, not all fish have bubbles, such as sharks (of the cartilaginous fish class) do not have bubbles inside the body. Many of the fish we eat often don’t have bubbles either.
In fact, to swim freely in the water, fish mainly rely on the movements of pectoral and pelvic fins to float and dive in the water. Although the bubble does not have the ability to actively adjust, it has the effect of providing stability, reducing gravity, allowing the fish to float to a certain depth without swimming. Thanks to that, a lot of energy is saved.
When the fish dives due to the movement of the fins, the size of the bubble decreases due to the increased pressure and the deeper it sinks the more buoyancy decreases, this passive change can help the fish dive.
Likewise, when a fish floats, the size of the bubble increases due to the reduced pressure, and the more it floats near the water surface, the greater the buoyancy. Simply put, the role of a bubble is to match the overall depth and pressure of the fish to its habitat.
But this is an unstable balance and floating or diving disrupts the balance, causing the fish to need more energy to get back into equilibrium. It is similar to a small ball placed on top of a slope, will roll forward or backward and only a small area on top can maintain balance. If you put a fainted fish into a container, it will float above the water in its natural state. But when the pressure increases to simulate the deep underwater environment, after the pressure reaches a certain level, the fish sinks to the bottom.
Conversely, fish living in the deep sea will emerge quickly, passively dilating the bladder, so it will be difficult to return to the old depth, if too much effort can cause the bubble to burst. When fishermen live at depths of more than ten meters, they can easily find that their bubbles will not be intact. Some will have visceral rupture due to overly expanding bubbles.
It can be said that, for most fishes, the bubble’s role is not as a lift that actively controls the rise and fall, but as a regulator so it can adapt to the aquifer where they live. through slow and slow air intake and exhaustion.
A fish’s bubble in deep water is different from a fish’s bubble in shallow water.
But for bottom-dwelling fish, the bubble’s role is relatively small and it is often degraded. Other fish species often have to swim fast for long periods of time and the bubbles are less developed.
For some fish species that live in extremely shallow water, they may not need bubbles to adjust their buoyancy. Some species like African lungfish, to survive the dry season, they often go into the mud to sleep. The bubble can now play a role similar to that of a “lung”.
Some species use bubbles as a tool to flirt with each other. They can make a loud noise by friction between the bubbles with the muscles and the vertebrae.
Some species evolved to make the bubbles larger and thicker, eventually becoming the ultimate cooking ingredient.
Bubbles of some fish have become favorites.