Indeed, why can’t fish live on land, and we can’t live under water? Do fish breathe - of course, because they have both lungs and gills, with the help of which fish breathe. Well, why don’t they live on land then?
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 releasing 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 will not have time to release oxygen from the water so quickly so that the tissues do not have time to experience oxygen starvation.
Fish gills come into a state of stupor, immobilization, when the fish hits land - they begin to work convulsively, but as they dry out, they work worse and worse until they stop moving completely. Then the fish dies.
With evolution, fish have adapted to live in water and their gills can no longer work on land. Therefore, caught fish is watered with water to keep it alive. They especially try to water 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 Mudskipper goby fish can crawl on the ground like a small lizard and swim in the water like a real fish. These fish are also called mudskippers.
Also creeping freshwater fish - perch and mangrove fish Rivulus. For example, a creeper fish, the perch and perch - it is sometimes called a climber, because it can even climb a non-steep bank. These perches live in Asia - in India and China. On land, this perch breathes not with gills, but with a special labyrinth - an organ located in its head. They say that this perch can even climb palm trees.
Watch the video - how fish can live and even run on land:
Mangrove fish can survive without water for up to two months. In these fish, the gills become stronger and change when they come to land, but when the fish enter the water, the gills restore their condition.
This is what these fish look like:
Now you know why fish cannot live on land, and we cannot live under water - although there are some types of fish that can live on land for a short time.
Spiders feed on insects: they produce a sticky thread and weave a network from it - a web; insects fall into this network, become entangled, and the spider eats them. However, there are several species of spiders whose bite is poisonous, such as the tarantula and the black widow.
The tarantula is a very large spider; its body is brown, with orange spots on its legs and abdomen. It lives in burrows dug in the ground. A tarantula can bite a person (if, for example, you accidentally step on it), but its venom is not much more dangerous than that of a bee.
The black widow is another poisonous spider, but only adult females pose a danger - males and young females have very weak venom.
Where is the scorpion's venom?
Scorpions, like spiders, have eight legs, and on the front of their head there are special processes - mandibles, with which they eat prey. But unlike spiders, the scorpion’s abdomen is divided into two parts: the legs are attached to the front part, and the back part is long, elongated and divided into segments: it is raised up and resembles a tail. At the end of this tail there is a so-called claw, which contains poison. Scorpions live in areas with arid climates, deserts and semi-deserts. During the day they hide from the heat under stones or under the bark of trees, and at night they hunt. Scorpions feed on insects and spiders.
Why do fish live in water?
Fish, like other animals, require oxygen to breathe; but they do not obtain it from the air, like land animals, but from water. On the head of fish there is a special respiratory organ - gills. Through the mouth, water enters the gills, and gas exchange occurs there: oxygen enters the blood from the water, and carbon dioxide is released into the water. After this, the water comes out through the holes in the gills.
The gills are hard plates with numerous blood vessels running from the inside of them, which give them their red color. In other animals, the respiratory function is performed by another organ - the lungs.
Can fish breathe on land?
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Most fish are unable to breathe air because their gills can only absorb oxygen dissolved in water. Therefore, fish die if left without water for a long time.
However, there are currently three surviving species of fish that have lungs and can breathe air. Australia is home to the Australian cattail, a lungfish that can live in stagnant water with little oxygen, as it can rise to the surface and breathe atmospheric air. A fish called lepidosirenus, which lives in South America, has no gills at all, it breathes only with its lungs; and Protopterus, which lives in Africa, can even get out onto land for a while.
Can fish see in the dark?
In the depths of the seas and oceans there is complete darkness, since sunlight is not able to penetrate more than 90-100 meters through the water column. However, many fish can live and see at great depths: the body of these fish is capable of emitting light, which illuminates surrounding objects and other fish. This property of fish is called bioluminescence.
Many deep-sea fish emit bluish light, and their eyes can only detect the blue part of the light spectrum. Other fish emit a red light, which they themselves distinguish, but other fish do not; therefore, they can see their prey and approach it without being noticed. Male fish also use this light to attract a female. In some deep-sea fish, light is emitted not by the entire body, but by individual organs specially designed for this.
If you carefully examine the head of the fish, you will notice a bony plate that is fused with the head closer to the eye and can open from the side of the body. This is a gill cover; lift it and look inside, you will see a semicircular organ that looks like a flower petal - these are gills - the respiratory organ of fish.
How do fish get oxygen?
Like any living creature on Earth, fish need oxygen, as in the air, it is dissolved in water. Of course, in a liquid environment its amount is less, but it is quite enough for fish to breathe. 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 muddy water, these are carp, tench, catfish, and so on. But others (for example: trout, sterlet) can die in such water; they need clean water with a fast current. The amount of oxygen in water depends on the time of year. In summer, when the temperature is high, the oxygen content in liquids decreases, the same thing happens in winter, when the reservoir is covered with thick ice.
The gills of fish are designed in such a way that oxygen dissolved in water is absorbed, just like in human lungs. A huge number of blood vessels penetrate the gills, so oxygen instantly enters the blood. The blood of fish, like human blood, immediately carries the necessary gas to all cells of the body. The mouth cavity of the fish has a wide passage that ends in gills. By opening its mouth, the fish fills the cavity with water, oxygen is absorbed by the gills, and water is released through the gap between the body and the gill cover when the fish closes its lips tightly and opens the covers.
Can fish breathe on land?
In nature there are fish that can stay out of water for quite a long time. For example, one of the varieties of perch (also called “Climbing Perch”) that lives in the Far East. The gills of this unusual fish are designed in such a way that they can absorb oxygen from the air. In addition, the perch has unusual scales. Due to the fact that it is mobile, the fish can “go ashore” and even climb trees (that’s why the perch is called “climbing”).
Another fish that can breathe air is the Mud Skipper. It lives in Africa, where in the summer the rivers dry up completely. The skipper buries himself in the mud and lies without water and practically without air for several months. When water reappears in the river, the mud skipper can emerge from it with the help of very developed fins and move quite quickly along the bank.
Why do fish taken out into the air die? - Children usually answer that their gills are drying up. 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 there is humidified.” Well done. And when sinister physical trainers force you to 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 (closing) of the gill filaments: they are designed to support water and “fall off” in the air. You might have seen this if you took “fluffy” algae out of an aquarium - when exposed to air, they immediately lose their fluffiness and turn into slimy lumps.
The solution to the problem is to reinforce the gills, that is, insert skeletal elements into the gill petals so that the petals do not fall off. Why fish don’t do this is understandable: they are aquatic inhabitants and, generally speaking, do not go to land.
Are you sure they're not going to?
Goofing off with fish is a human activity, but somehow you expect more reasonable behavior from fish. And here - on you! They're climbing! On land! ...In the same way, any old geezer says about young upstarts: “Look, he’s so smart!” - forgetting that 500 million years ago he himself was absolutely the same.
Paleontologists say that all terrestrial vertebrates are distant descendants of fish that once crawled onto land. “That’s why we’re so worried and shout to the fish: “It’s already busy here, crawl back!” Pisces respond: “Come on, we’re not going to live on your land, we just need to wait out the drought/heat/low tide/pollution!”
Drought. The fish living in fresh water bodies are most unlucky. In particularly hot places, such reservoirs can dry up, and then what to do? Either die or go look for another body of water. It is clear that the fish try to do this on a damp and dewy night, but still - they crawl on dry land!
Heat. However, even without drying out, you won’t get bored in a fresh body of water in the summer: there is very little oxygen in warm water, and almost none in hot water, so there is little benefit from such water (in terms 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 heats up, their metabolic rate increases automatically.
Low tide. The Moon, flying around the Earth, forms a small . When this tubercle is with us, the tide comes, when it is not with us, the tide comes. Fish that do not want to leave their native (rich in food) intertidal zone during low tide remain on the free land (rather, thinner).
Pollution. By the way, about the liquid. Gills, according to their original purpose (remember the lancelet) are filters that retain various aquatic fines. If for some reason there are too many microscopic particles in the water, then the fish gills can simply become clogged, like toilet bowls.
We reinforce the gills
1 - gills of ordinary fish in water.
2 - the gills of ordinary fish stick together in the air. Because of this, the surface through which gas exchange occurs (circled in black) decreases sharply.
3 - reinforced gills: a bit rough, but reliable.
An example of reinforced fish are mudskippers that live in the intertidal zone of the 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 they climb the aerial roots of coastal mangroves” (BSE), climbing onto height up to 2 m.
We breathe through the surface of the mouth and gill cavities
Labyrinth fishes breathe mainly with the help of labyrinth- an organ located above the gills and in structure reminiscent of our nasal cavity (many thin bone plates covered with a mucous membrane with a large number of blood vessels). In the picture there is a cut up pinnabas (a creeper, its labyrinthine organ looks like a lump of crumpled paper). The second name of the Anabass speaks for itself - it crawls.
The leader of the (sub)order of labyrinths is the gourami fish, known from aquariums, which in nature grows up to 60 cm. The Latin name gourami (osphronemus) means “smelling” - the zoologist who described it saw how often it floats up and draws in air, and considered that it sniffs out something. In fact, she breathes like this, and if she is deprived of the ability to float, the gourami will suffocate (its 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 easily catch a cold.
Tropical catfish increase the surface of their epibranchial organ more simply - without any tricky labyrinthine folds, they simply extend it along the body, resulting in a bag similar to a primitive lung.
Breathe with your lungs
Bony fish originally arose on land, which meant they immediately faced drought, heat, and pollution. Most likely, the oldest bony fish originally had lungs and used them for breathing. Then, with the course of evolution
- some bony fish crawled onto land and remained there forever, turning into ancient amphibians (they are not in this article, because it is about fish);
- some bony fish returned to the ocean, where there are no big problems with oxygen, so their lungs turned into a swim bladder (see below);
- Some bony fish remained to spend the winter on land, so they breathe with their lungs quite calmly (right now).
Modern lungfishes breathe with their lungs - the meter-long Amazonian lepidosiren, the two-meter Australian cattail, and three species of African protopterans. The latter among fish are champions of anhydrous life: when the reservoir completely dries out, they can bury themselves in the ground and sit there 5-9 months breathing atmospheric air.
We breathe through the swim bladder and/or intestines
Open-vesical fish (those whose swim bladder is connected to the esophagus) introduce air into the swim bladder by simply swallowing. Therefore, while the air bubble is moving through the esophagus, and after that, 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 bladder, up to 75 cm long, remains alive in the air for 24 hours.
Loaches (see the first photo of the article) feed on air, just like you and I feed on semolina porridge. The hind intestine directly performs the function of gas exchange. Loaches swallow air, air bubbles pass through the entire intestine, gas exchange occurs in the hindgut, and the bubbles are expelled through the anus. I think it's quite troublesome.
Breathe with the surface of the body
Our body surface (in animals, unlike plants and fungi) is relatively small, so use it as basic only leisurely ice fish can source oxygen (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 refused hemoglobin and red blood cells).
