Wow! That’s fascinating! I’ll have to add the aquarium to my bucket list. 🙂
That second picture (the one with the silhouettes in front of the tank) could sell! I could just imagine it being in a magazine advertisement for the aquarium or something.
I would carefully Photoshop out the line that’s about half way through the image (probably a seam in the glass). Since this is such an awesome composition, I would also probably keep shooting this scene until I felt I had captured a better assortment of creatures arranged in the tank. Right now the center is empty and the awesome school of yellow fish on the right is overlapping the less brilliantly colored fish behind them.
ISO 800 isn’t bad, really, for such low light! Just use noise reduction in post processing (like it looks like you did).