It will be harder to photograph your fish. First you are limited by how close you can get - e.g. if your tank is a 18 inches wide, and the fish is at the back glass, you are going to be 18 inches away. And then by how little light there is in the tank. Flash and or very fast prime lenses are your friend. Depending on camera the onboard flash may or may not work without glare from glass. The good thing is that fish cannot run away too far - if you missed your shot, just wait until they decide to swim by again.
Nice pictures you got there.