Absolutely all living things need oxygen. They can take it from atmospheric air or water. But how do fish breathe? They do not have organs as complex in structure as the lungs. But fish have gills. They help to absorb this gas during breathing. At the same time, they function much more efficiently than our lungs, because they are able to take up to 30% of the oxygen dissolved in it from water. But in reality, fish have a lot more breathing methods. All of them developed as a result of a long evolution and are inherent only to certain species.
How do gills breathe fish?
Of course, all fish, without exception, have gills. Their shape is diverse. In some species, these are sacs, in others, plates or petals. But all these devices are aimed at one thing - the creation of a larger surface penetrated by a dense network of capillaries, with a relatively small amount of space.
Water with oxygen dissolved in it enters through the throat at the moment when the fish opens its mouth wide. The gills themselves are quite delicate organs, so a dense gill cover covers them from above. She also takes a direct part in breathing. At the moment when water enters the pharyngeal cavity, gill covers fit snugly to the head. So they prevent the outflow of fluid. When the gill covers open, the pressure changes and water enters a special cavity. It is penetrated by a dense network of blood vessels. Gill arches are straightened, and gas exchange process occurs. Oxygen enters the blood, and not only carbon dioxide, but also metabolic products are removed from it. Water comes out of the gill cavity through special gaps. This is how the fish breathe.
Fish that breathe through the skin
Of course, fish breathe with gills. This is known to all. But then, how can one explain the fact that some species that appear outside the water, in moist grass or earth, can live there for several hours? How do fish breathe in such conditions? Certainly not through the gills.
A number of species, such as crucian carp, eel, carp, carp, in the process of evolution have an additional opportunity. They can absorb oxygen across the entire surface of the skin. This is especially true when the level of this vital gas in the water drops to a critical level. Then the gills become ineffective, and skin respiration comes to the fore.
How do labyrinth fish breathe?
Many aquarium owners have noticed how the fish breathe. They often swim to the surface of the water and stick their head out a little. Why are they doing this?
Many varieties of aquarium fish have a specific respiratory organ - the labyrinth. With its help, they can actually absorb oxygen not from water, but from atmospheric air. In this case, the fish should at least once every few hours rise to the surface and take a breath. Otherwise, she will die.
The gill maze is located on both sides of the fish head. It is located above the gills. When a fish swallows an air bubble, it enters the spongy chamber of the maze. Their walls are densely covered with capillaries. Oxygen penetrates into them, which then spreads to all organs and tissues of the body. The gill maze helps fish not only survive in an oxygen-depleted pond, but also to move to another.
Intestinal fish
This may surprise many, but there is one kind of fish that uses the intestines to breathe. These are catfishes of the genus Coridoras. They breathe atmospheric air. Although this is not entirely true. Unlike the same labyrinth fish, they have no special organs. Speckled catfish are able to absorb oxygen in their stomach. This is a fish that breathes air. She just swallows it and pumps it into the swim bladder. Here the assimilation of oxygen occurs.
Trees able to climb trees
So, what fish breathe in water is quite understandable. But what about those that can be out of the water for several days? Do you think these do not exist? Not at all. A striking representative of such fish is the climbing perch. He lives in the Far East.
The gills of this unique fish are designed so that it is able to absorb oxygen from the air. In addition, she has a special structure of scales, which allows her not only to move on the ground, but also to climb trees. Actually, for this feature, it got its name.
By the way, this species is far from the only one. There is another fish that can breathe air - it is a silty skipper. It lives in areas of Africa where severe droughts are often observed. This fish has developed an interesting way to survive these unfavorable periods. When the pond dries up, the skipper buries in the sludge. There he is able to be without water for several months. Only when water comes again does he leave his makeshift shelter. This is what most double-breathing fish do. This group deserves special attention.
Lungfish
Lungfish belong to a very ancient group. Paleontologists find the remains of these creatures in the layers and sediments of the
Paleozoic era. For quite some time they were considered a completely extinct species. And only after studying the nature of Australia and Africa in the 19th century, a stunning discovery was made. Modern species of double-breathing fish were found. This not only influenced the views of scientists regarding the systematics of vertebrates, but also made its own adjustments to
evolutionary doctrine.In addition to the characteristic gills, all bipedal fish also exhibit one or a pair of lungs. This is a modified swimming bladder. These organs have nothing to do with the lungs of mammals. Their walls are penetrated by numerous capillaries, through which gas exchange occurs. Do fish breathe oxygen dissolved in water? Of course. But only when it is enough in the water. They need lungs only in order to wait out a long period of drought, walled up in silt, or in order to move from one reservoir to another. As a rule, they have highly developed fins that are able to play the role of limbs. So, bipedal fish can make transitions lasting even several days.