HSU 15" sub and aquariums

Don't really know. But this article might make you want to keep the volume at a low listening
level......http://www.sciencedaily.com/releases/2003/02/030210075908.htm

They'll be fine they are floating/swing in a water column.

I am indeed an noob to the av world but not to fish keeping. In short, sounds or vibrations that travel through air are one thing, but direct vibration through solid matter is an entirely different matter which will affect fish. "Do not tap the glass" at the fish store aquariums are there for a reason. Loud music from my speakers never really bothered my fish....but slam a door in the house and watch them dart.

This sounds like one of the few legitimate instances where a subwoofer isolation pad would be warranted.

careful with the sub by the fish tank. I read a online review along time ago about a guy using big power amps at 400 watts blowing the glass out of his fish tank with two cerwin vega ve15 inch speakers.

I would bet your fine. I hit ~130+ DB in my room doing some extreme testing(cracked ceiling, etc). Fish tanks were fine. 55gallon oceanic(over thick glass) but also some cheaper ones with thin glass 29/128/10. All the tanks are rather old too so the seals are probably not as strong as they were at one point.
I cant find it currently but I read somewhere due to the water it is absorbs almost all the energy stopping the glass from any form of normal vibration that say windows would experience. As for the fish... they didn't seam to mind but i didn't ask them :\

Anyone who's watched Finding Nemo knows this!

Craig