This is a very very good capture, this is one of the hardest shots to get without getting reflections from the glass. Excellent Job!!! I really like your subject as well, looks like your subject had a lot of practice.....lol I gave it a 10
How I did this was I actually turned off flash (The animals don't like flash), and then I pressed the lens up against the glass. I believe the tank was lit from the inside, made it much easier.
You should name him "Spike" :P
Nice work!!