Hellabrunn in München is not really fish-oriented. They restructured a few years ago, though, and it might be different now. If you want to see a big public aquarium go to Konstanz at the Bodensee. They have a very new and fairly large exhibit.
Regarding LFSs: Check out the aquarium store on Lindwurmstraße in München. http://www.aquarium-center.de/
Their website isn't all that great, I posted it for their contact information. The store is awesome.
Too bad you didn't post where you're at, nor did you enter your location in your profile