Well, I suppose water vapor also. What I meant is that water also has dissolved CO2 (carbonic acid) and O2 (what fish breathe). Not sure what, if any, other gases are normally present dissolved in water.

What I'm not sure about is whether they'd be liberated when the air pressure goes down. I suppose so, since that's how your lungs remove CO2 from your bloodstream. But is it enough to make a difference?