Fish can use gills for breathing. Unlike terrestrial animals, which use lungs to breathe, fish gills can only function in the water. There are gill filaments under the gill cover, and the gill filaments are densely covered with blood vessels. When water flows through the gills, because the flow direction of water and blood is opposite, it can carry out efficient gas exchange, so as to obtain oxygen and discharge carbon dioxide.
In addition to gills, there are some fish with auxiliary respiratory organs, including the African lungfish can rely on swim bladders to breathe. Lungfish are called lungfish because their swim bladders are special, similar to the lungs, with small air chambers around the central cavity, which are divided into small air sacs that store oxygen and allow them to continue breathing for a period of time after leaving the water.
The mudskipper is a small fish that lives in warm coastal waters. It generally inhabits shallow waters along the coast. When the tide ebbs, it can move on the ground to feed. The reason why the fish will not die out of the water is that the skin and oral mucosa to breathe, but before drying, they still need to return to the water.
At the bottom of rivers, lakes, and paddy fields, there lives a kind of fish called loach. They live in the daytime and come out at night. They have strong adaptability. When the water body is short of oxygen, this kind of fish can swim to the surface and swallow the air into the intestinal tract to breathe. Before the pool dries up, they can survive by diving into the mud.
