So have you ever wondered how fish breathe underwater? Do they have lungs like us humans? If so, why don’t they drown?
Fish and humans resemble each other in many ways. We have digestive, circulatory and nervous systems similar to those of other vertebrates. Naturally fish need oxygen as much as we do in order to live, so what do they do when swimming? Do they just hold their breath like we do?
What makes a fish stand out from other animals is it’s respiratory system, a fish’s respiratory system is mainly determined by the fact that it lives underwater.
As I’m sure you know, the chemical formula for water is H2O, in simple terms that means that for every 2 parts of hydrogen there is 1 part oxygen. So there IS oxygen in water. So fish just need a system that can extract that small amount of oxygen out of the water and into their bloodstream. They use their gills for this, these are found between the mouth and the pharynx.
In the interests of keeping this next bit simple I won’t go into all the details on the respiratory system, basically water flows into the mouth, through the gills, and out of the body through gill slits. As water flows through the gills, the oxygen it contains passes into the blood circulating through gill structures called filaments and lamellae. At the same time, carbon dioxide in the fish’s bloodstream passes into the water and is carried out of the body
