What oxygen in the water do fish use?

“Oxygen gets into water by diffusion from the surrounding air, by aeration (rapid movement), and as a waste product of photosynthesis.”

Gas. Liquid oxygen literally freezes things it touches.

http://en.wikipedia.org/wiki/Liquid_oxygen

Fun fact. Fish can be drowned

Gills extract dissolved oxygen from water. It’s technically not a gas at that point because it doesn’t display the physical properties of a gas. In its dissolved form, individual oxygen molecules are trapped and isolated between water molecules. An isolated molecule can’t be said to have any particular physical state.

Dissolved oxygen (d. o.)

Kind of like sugar dissolved in water – neither solid nor liquid.

Fish don’t breathe oxygen.. they breathe cheese spray.. duh