Aquarium lighting is usually not sufficient to take good detail picture of the fishes even with high iso especially consumer camera and that may be the reason for shake. You will need to find ways to lit up the tank from the top and from the sides, flash or other lighting source. I supposed u can google for answer.
I think quite hard.... Coz if you're shooting at the long end + bad lighting = big aperture = thin DOF = blur images.
With a consumer cam, I think your best bet is:
1) Have so much light such that you can shoot at: f11 + 1/500s (at whichever ISO)
2) Shoot at the wide end so you will have more DOF.
3) Take all sharp shots of the tank, then crop as needed.
4) artificially gaussian blur out the bg if you really die die want bokeh