*hits blunt* If humans can’t see air; can fish see water? But since humans can see water, can fish see air?

No, they won't see the air if they come above the water, but their eyesight may be less effective just as ours is if we submerge ourselves.

I imagine they can see the water surface from below, though, just as we can in fact. (Though it's a lot easier for us if we wear a diving-mask when in the water, or we are looking obliquely up through an aquarium).