How Can Fish Breathe Underwater?

In many ways the inside of a fish is practically the same as throughout all kinds of fish. The only thing that makes a fish different is there respiratory system. Fish evolved not having to make frequent trips to the surface to get air, like marine mammals. So instead they have developed gills on which they rely on to get oxygen for their limited metabolism. Fish use their gills to extract the oxygen from their watery environments. How it works is the fish has to open their mouth and the operculum closes the mouth which allows water to flow into the mouth pumping water through the gills thus makes it breathe. There are other fish that don’t really have this unique capability; they instead have to constantly swim in order to create oxygen. Once the water is in the mouth it continues to the gill rakers. Gill rakers are a filtering system for the gills, which pump out any food materials. After that is done the water leads itself to the gill arches, which are suspended between the mouth cavity and the operculum. Each gill is made up of little gill filaments, which are extremely thin membranes poking out into the water flow. Each of the gill filaments are layers with rows upon rows of lamellae. The water flows across the lamellae, and oxygen and carbon dioxide are exchange directly across the capillary membrane. Fish are very talented; they can extract 85% of the oxygen that is in the water, but there is actually 2-5% of oxygen actually in it. It’s funny because some fish have nostrils, but those are only used to smell and play no role in the respiration.