Students of Class 4 have experienced Respiratory System of Fish. during the experiment their teachers practically has shown them and explained that Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills. The gills lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by the gill arches and filled with blood vessels, which give gills a bright red colour as in picture in below. Water taken in continuously through the mouth passes backward between the gill bars and over the gill filaments, where the exchange of gases takes place.
