Gill anatomy - the location

Fish breathe by taking up oxygen from the water. Instead of lungs, the fish have gills that do this. As you'll se later on, taking up oxygen from water is more difficult than from air. That's why the breathing of a fish can often encounter problems; you could say that the fish is closer to running out of oxygen than are we land living creatures. There are four gills arches on each side of the head, as indicated in the figure to the right. Each gill arch is composed of a huge number of gill filaments that in turn contain the respiratory unit called gill lamella (this will be clear later on). The fish take in water through the mouth and the spece before the gills is called the buccal cavity. The water then flows across the gills and enters the opercular cavity. At the same time blood is pumped through the gills by the heart. Go on to the next step and read more about the gills and where the exchange of oxygen between the water and blood takes place.