How do fish breathe underwater?

gill respiration

Fish breathe through the gills to obtain oxygen under the water, and humans get oxygen from the air. The gills are a row like a hairbrush extending in lines that go towards the body of the fish from the outside. The fish has at least three gill arches, and some fish have seven arches.

Jeffrey Mallison, director of the aquaculture program at the University of Wisconsin-Madison, says that the gills in fish do the work of the lungs in mammals, and their main function is gas exchange, that is, taking oxygen and excreting carbon dioxide, and the gills and lungs contain a group of very small blood vessels on their thin walls to allow gas exchange through them.

The function of the gills is much more difficult than that of the lungs, the air entering the lungs contains 20% oxygen (meaning it contains 200,000 parts per million), while the water contains a much smaller percentage, estimated at between 4.8 parts of oxygen per million. of water, which means that breathing underwater is quite challenging for fish, and requires a lot of energy from their bodies,[٢] Where the small blood vessels take oxygen and distribute it to the body of the fish, where the water enters through the mouth, as when a person breathes through his mouth, and then the air passes through the gill arches, blood vessels and blood vessels. The gills, then the capillaries take it and send it to the rest of the body of the fish, and then the water comes out from the other side through the gills.