Saw, how do fish breathe underwater question, and just had to answer the closed question.?

When A water molecule binds together it does it via a covalent bond, sharing of electrons, but when you have many water molecules the seperate H2O molecules bond together through hydrogen bonding, thus connecting all the molecules together. These molecules create a sort of framework that trap AIR, yes the same air you and I breathe. Thus the gills on a fish do nothing but filter out the trapped air in water, which is close to 20 % oxygen the same as regular air. Distilled water has very little trapped air in it, if any, if fish are put in distilled water with no aerator they will die. Thats all an aerator does is replace the trapped air in water. A neat experiment is to take 500 ml of Isopropyl Alcohol, and 500 ml of tap water, mix them in a 1000 ml grauated cylinder, stir occasionaly and watch the water level drop. The Alcohol breaks up the Hydrogen bonds and releases the trapped air, you will see all the tiny air bubbles in the solution. Well there you go!!!!