If you carefully examine the head of a fish, you can see a bone plate that has grown together with the head closer to the eye and is able to open from the side of the body. This is the operculum, lifting it and looking inside, you will see a semicircular organ, similar to a flower petal - these are the gills - the respiratory organ of fish.
How do fish get oxygen?
Like any living creature on Earth, fish need oxygen, like air, it is dissolved in water. Of course, in a liquid medium, its amount is less, but it is quite enough for the respiration of fish. Oxygen enters water from the atmosphere. The cleaner the water and the faster the flow, the higher the oxygen content in it. Some fish can live in bodies of water with a slow current (or without it, for example: ponds, lakes) and turbid water, these are carp, tench, catfish and so on. But others (for example: trout, sterlet) can die in such water, they need pure water With fast flow... The amount of oxygen in water depends on the season. In the summer, when the temperature is high, the oxygen content in the liquids decreases, the same happens in the winter, when the body of water is covered with thick ice.
The gills of fish are designed so that oxygen dissolved in water is absorbed, as in the lungs of a person. A huge number of blood vessels penetrate the gills, so oxygen instantly enters the bloodstream. Fish blood, like human blood, immediately carries the necessary gas to all cells of the body. The mouth of the fish has a wide passage that ends in gills. Opening the mouth, the fish fills the cavity with water, oxygen is absorbed by the gills, and water is thrown out through the gap between the body and the operculum when the fish tightly compresses the lips and opens the lids.
Can fish breathe on land?
In nature, there are fish that can be out of the water for a long time. For example, one of the varieties of perch (also called "climbing perch"), which lives in the Far East. The gills of this unusual fish are designed so that they can assimilate oxygen from the air. In addition, the perch has unusual scales. Due to the fact that it is mobile, the fish can "come ashore" and even climb trees (this is why the perch is called "climbing").
Another fish that can breathe air is the Mud Skipper. It lives in Africa, where rivers dry up completely in summer. The skipper burrows into the silt and lies without water and practically without air for several months. When water reappears in the river, the oozy skipper can come out of it with the help of very developed fins and move quite quickly along the bank.
Indeed, why can't fish live on land, while we are under water. Do fish breathe - of course, because they have both lungs and gills, with the help of which fish breathe. Why shouldn't they then live on land?
All this is the result of evolution. Man has adapted to live on land and our lungs are capable of absorbing oxygen from the air and emitting carbon dioxide. If human lungs are filled with water, then given that although there is one oxygen atom in a water molecule, there is still very little of it and human lungs simply do not have time to release oxygen from water so quickly that the tissues do not have time to experience oxygen starvation.
Fish gills, on the other hand, come into a state of stupor, immobilization, when the fish hits the land - they start to work convulsively, but as they dry up, they work worse and worse until they completely stop moving. Then the fish dies.
With evolution, fish have adapted to live in water and the gills can no longer work on land. Therefore, the caught fish, in order to keep it alive, is watered. They especially try to pour water on the gills so that they do not dry out and the fish does not die.
Fish that can live on land
However, there are still fish that can live both on land and in water. For example, the goby fish Mudskipper can both crawl on the ground like a small lizard and swim in the water like a real fish. These fish are also called mudskippers.
Also creepers freshwater fish- perch and mangrove fish Rivulus. For example, creeper fish perch pineapple - he is sometimes called a climber, because he can climb even a steep bank. These perches live in Asia - in India and China. On land, this perch does not breathe with gills, but with a special labyrinth - an organ located in its head. It is said that this perch can even climb palm trees.
Watch the video - how fish can live and even run on land:
Mangrove fish can go without water for up to two months. In these fish, the gills are strengthened and changed when entering land, but when the fish re-enter the water, the gills regain their condition.
This is what these fish look like:
Now you know why fish cannot live on land, and we are under water - although there are some types of fish that can live on land for a short time.
Why do fish that are taken out into the air die? - Children usually answer that their gills are drying out. But the surface of our lungs also comes into contact with dry air - why doesn't it dry out?
Children say "we breathe through our nose, and the air is humidified there." Well done. And when sinister physical trainers make you run 10 laps, do you also breathe through your nose? No, you breathe through your mouth, it is wide open, and your tongue lies on your shoulder.
The reason for the death of fish in the air is the sticking together (closing) of the gill petals: they are designed to support water and “fall off” in the air. You could see this if you took out "fluffy" algae from the aquarium - in the air they immediately lose their fluffiness and turn into slimy lumps.
The solution to the problem is to reinforce the gills, that is, to insert skeletal elements into the gill petals so that the petals do not fall off. Why fish do not do this is understandable: they are aquatic inhabitants and, generally speaking, do not gather on land.
Surely not going to?
Fat with fat - human occupation, but somehow you expect more reasonable behavior from fish. And here - to you! Climbing! On land! ... In the same way, any old old man says about young upstarts: "Look, he was smart!" - forgetting that 500 million years ago he himself was exactly the same.
Paleontologists say that all terrestrial vertebrates are distant descendants of fish that once crawled out onto land. - That is why we are so excited and shout to the fish: "It's already taken here, crawl back!" Pisces answer: "Come on, we are not going to live on your land, we would only have to wait out the drought / heat / low tide / pollution!"
Drought. Most unlucky fish living in fresh water. In especially hot places, such reservoirs can dry up, and then what to do? Either die, or go to look for another body of water. It is clear that fish try to do this on a wet and dewy night, but all the same - they crawl on land!
Heat. However, even without drying out in a fresh reservoir in summer you will not get bored: there is very little oxygen in warm water, and there is almost no oxygen in hot water, so there is little benefit from such water (in the sense of breathing). And as luck would have it, more oxygen is required than usual - after all, fish are cold-blooded animals, and when the water is heated, their metabolic rate increases automatically.
Low tide. The moon, flying around the earth, forms a small one. When this bump is with us, the tide comes, when not with us, the ebb. Fish that do not want to leave their native (rich in food) tidal zone, during low tide, remain on the freed land (rather, thinner).
Pollution. By the way, about the slurry. The gills, according to their original purpose (remember the lancelet), are filters that trap various water fines. If, for some reason, there are too many microscopic particles in the water, then fish gills can simply clog up, like toilets.
Reinforcing the gills
1 - gills of common fish in water.
2 - the gills of ordinary fish stick together in the air. Because of this, the surface through which gas exchange takes place (circled in black) sharply decreases.
3 - reinforced gills: rough, but reliable.
An example of reinforced fish is the mudskippers found in the intertidal tropical Pacific and Indian Oceans. At low tide, they remain on land, but do not lie stupidly among the silt and do not wait for some rat to eat them, but with the help of their powerful fins "with amazing dexterity climb the aerial roots of coastal mangroves" (TSB), climbing height up to 2 m.
We breathe with the surface of the oral and gill cavities
Labyrinth fish breathe mainly with the help of maze- an organ located above the gills and in structure resembling our nasal cavity (many thin bone plates covered with a mucous membrane with a large number of blood vessels). In the picture, a pineapple is cut (a creeper, its labyrinthine organ looks like a wad of crumpled paper). The second name of the climbing perch speaks for itself - it creeps.
The leader (sub) of the detachment of labyrinths is the gourami fish, known from aquariums, which grows up to 60 cm in nature. The Latin name gourami (osphronemus) means "smelling" - the zoologist who described her saw how often she floats up and draws in air, and considered that she sniffing out something. In fact, she breathes like that, and if you deprive her of the opportunity to float, then the gourami will suffocate (her gills are underdeveloped - therefore, these fish can drown). If, on the other hand, you leave the aquarium with gourami open, then the fish, breathing too much fresh air can catch cold easily.
Tropical catfish increase the surface of their supra-gill organ easier - without any tricky folds-labyrinths, they simply lengthen it along the body, resulting in a bag that looks like a primitive lung.
We breathe with our lungs
Bony fish originally originated on land, which means they immediately faced drought, heat and pollution. Most likely, the earliest bony fish originally had lungs and used it for breathing. Then with the course of evolution
- part bony fish crawled out onto land and stayed there forever, turning into ancient amphibians (they are not in this article, because it is about fish);
- some of the bony fish returned to the ocean, where big problems there is no oxygen, so their lungs turned into a swim bladder (see below);
- some of the bony fish remained to winter on land, so they breathe with their lungs quite calmly (right now).
Modern lung-breathing fish breathe with their lungs - the meter-long Amazonian lepidosiren, the two-meter Australian horntooth, and three types of African protopters. The latter among fish are champions in anhydrous life: when the reservoir is completely dry, they can burrow into the ground and sit there. 5-9 months breathing atmospheric air.
Breathing in a swim bladder and / or intestines
Open-bladder fish (in which the swim bladder is connected to the esophagus) move air into the swim bladder by simply swallowing. Consequently, while the air bubble is moving along the esophagus, and then, when it has already entered the bubble, oxygen can be absorbed from it if desired. An example is the North American mud fish (pictured), has a cellular bubble, up to 75 cm long, remains alive in the air for a day.
Loaches (see the first photo of the article) feed on air, as we eat semolina porridge. Directly the function of gas exchange is performed by the posterior part of the intestine. Loaches swallow air, air bubbles pass through the entire intestine, gas exchange occurs in the hind intestine, bubbles are thrown out through the anus. Quite troublesome in my opinion.
Breathing with the surface of the body
Our body surface (in animals, as opposed to plants and fungi) is relatively small, so use it as basic oxygen source can only be unhurried ice fish(once again: fish are cold-blooded animals; at a temperature of 1-2 ° C, their metabolism is very slow, there is enough oxygen - ice fish even abandoned hemoglobin and erythrocytes).