How do fish breathe? (Video for children)
Fish, like land animals, need oxygen. Only it doesn't breathe oxygen in the air, like us, but oxygen dissolved in water.
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The respiratory organ of the fish is the gills. They are located in the oropharyngeal cavity, placed in four pairs of cartilaginous plates: branchial arches, and at the top they are covered with gill covers bordered by a smooth and leathery edge.
The branchial arches have branchial stamens on the inner side and branchial lobes on the outer side.
Branchial petals:
These are the elements of the gills as respiratory organs. They are penetrated by a large number of small blood vessels and are therefore pink in color. In the gill lobes, oxygen is absorbed from the water as it passes through the gills.
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Branchial stamens are a filter by which fish retain small live foods from the water in their mouths. Therefore, water already purified from mechanical impurities enters the gill lobes from the oral cavity. Depending on the type of fish, the stamens are different in shape and quantity.
Predatory fish have tubers instead of gill stamens. But the fish that consume the smallest plant and animal plankton organisms have long, frequent, and numerous stamens. In white fish, when eating large animal food stamens are short, rare and small.
The gill surface is 10-60 times larger than the body area of the fish.
The rhythmic movements of the gill covers cause a flow of water through the mouth, pharynx, and gills. When inhaled, the gill cover protrudes and the leather edge remains pressed against the fish's body. The branchial cavity increases in volume, and the pressure decreases according to the principle of a discharge pump, and water is drawn through the branchial arches leaving the pharynx.
When you breathe out, the gill covers are pressed against the body and the gill arches come together, preventing water from returning to the throat. As a result, the gill cavity decreases, the pressure increases, and the water passes through the leathery border and out.
For the normal functioning of the gills, a constant flow of fresh water is needed. When the fish is swimming, the water enters the mouth, washes the gills, and exits through the gill slits. When the fish stops, to open the gills continuously with clean water, always open and close the mouth, raise and lower the gill covers. Therefore, it absorbs fresh water and pushes old water.
In fish that leave the pond for a short time, for example, mudhoppers and eels, skin respiration accounts for 60% of total gas exchange.
In the absence of oxygen, some fish can breathe ... with their intestines! Fish like a catfish can swallow air and send it to the special section of the intestine with special movements that can exchange gases.