Wow.... Alot of uninformed opinions on quitting smoking and / or nicotine, when that was NOT at all what was asked in the original post.
Nano-nater, I am a 3yr vaping veteran. I have worked in a vape shop. I have educated myself as much as possible on vaping and have fought for vaping rights. So, hear me when I say, don't listen to these nay-sayers! Good for you for quiting smoking! I had high BP at 26 yrs old and now, I have great BP. My dr told me last month, that if he didn't know better, he would never have guessed that I ever smoked. So, congrats on making a healthier lifestyle choice.
Anyways, there is very little nicotine exhaled in the vapor. It's mostly VG, PG and some flavorings. But mostly VG, since that is what actually causes the visual effect of the vapor. My husband and I both use RDA's and it has never hurt any of my tanks. I wouldn't recommend blowing vapor directly into the tank or anything like that, but what gets in there, won't hurt anything. Look at the ingredients of the food you feed them. Any pellets, flakes, etc you feed probably have vg or pg in them. So, vg or pg won't hurt the fish.