Afish is resting in a shady part of the water, protected by surrounding rocks. the fish suddenly moves out into an open area that is sunny and closer to the surface of the water.

what is most likely the reason the fish moved?

to increase its body temperature
to slow down blood circulation
to obtain oxygen
to take in extra carbon dioxide

Atp is is our little "pocket" of energy. of course, if you have too little, then it means you have too little energy, and you'll pass out. the way to not have enough, is to have no energy sources (glucose, fats, proteins). you can't have too many atp molecules. cycles like the krebs cycle produce it, but if you have too much of any substrate (or too little for that matter), the cycle stops and atp is no longer made (it stops until substrate levels are such that the process can go on). in any case, this is unlikely since atp is constantly hydrolyzed and remade, even while you're asleep. you won't have too much. if you have zero, you are dead or dying.