Fish breathe with their gills. When they swim in the water, their mouths will open and close one by one, so as to swallow water, but water will not enter the body, but through the two gills, gill cover inside the gill filament, there are a large number of capillaries, but when the water passes through can complete gas exchange, so as to obtain oxygen.
1. Skin: In the northwest Pacific Ocean, there is a peculiar fish, whose name is mudskipper. The fish can not only survive in the water, but also out of the water for a period of time, relying on their skin and oral mucosa to absorb oxygen from the air by breathing, so that they can survive at low tide.
2. Intestinal tract: As we all know, loach is an animal that can live in mud, but it is also a kind of fish. The fish usually live in the bottom of the water, when the water oxygen deficiency, they will jump to the surface, will swallow air into the intestinal tract to breathe. And when the pool dries up, they can dive into the mud, as long as there is a small amount of water, they will not die.
3, swim bladder: In Africa there is a magical fish, called the African lungfish. This kind of fish can not only breathe with gills, but also breathe with swim bladder, the structure of swim bladder is similar to lung, there are many small air chambers around the central cavity, just like alveoli, and there are many small air sacs in the small air chambers, which can store oxygen for breathing.
