Fish, Breathing & Circulation
Fish are unique in that they have a specialized system used to extract oxygen from water as it is passed through its gills. The oxygen extracted from the water is then passed directly into the fishes blood stream. Bony fish have four sets of gills on each side of their bodies. these gills are blood like red, that is because they in fact are filled with flowing blood, which the oxygen is passed into.
A fish sucks water in through its mouth then pushes the water out through its gills. Its a common misconception that fish bring water in through their gills and out through their mouths. The water emerges from the open edge of its gill cover.
Once the oxygen reaches the fishes blood stream, the blood is known as enriched blood. The blood is then passed on to cells within the fish, when this happens carbon dioxide is formed and is passed back out into the blood. This carbon dioxide rich blood is then pumped into the fishes heart and back into the gills where the carbon dioxide is expelled.
There are a few types of fish that can actually breath through their skin and some can even breath air!
