I'm not sure if all of my suggestions were already posted, but I was too lazy to look through all the answers so here they are:
First, (like many have already said) fast shutter speed, and like many have already said add lots of light because fast shutter speeds do not allow much time for the light to enter the camera.
Second, depending on the grade of your camera (sorry if you said what camera it was before, but like i said i didn't read through it all

) you can lower the aperture number, also called f-stop, or f-number. Lowering this number means that you are widening the hole in which the light enters meaning more light can be let in. (Depending on how into this you want to get you could invest in a high quality DSLR that you can do this and manipulate shutter speed much more easily etc. personally i have a Nikon D80, but you could always go D40 which are cheaper and should have the same basic functions as my D80)
Third, like some have mentioned, a tripod. This will keep the back ground clear and everything. You could always place it on a chair or table.
For extra clear pictures with tripods or placement on table methods you can invest in a remote for your camera or merely put it on a short timer. Putting it on a timer and using a remote means that your finger on the shutter will not cause any vibrations. Because (as my photography teacher said) even the heart beat within your fingers can cause some movement and disruption.
As for adding lighting. Like someone mentioned the problem with using a flash on an aquarium is the reflection on the glass of the flash. To remedy this you can turn the flash off and supplement lighting. Add as many fluorescent lights as you can on top of the tank and add desk lights or warmer lights on the sides of the tank to hit fish on their sides so that not all the light is coming from the top (warmer on sides being my preference as to take out the cold coloring given off by the fluorescent lights). With extra lights on the sides of the tanks you do not need to deal with the reflection of the light on the front pane of glass. You can also experiment with putting lights in the front of the tank pointing towards the tank and using different shot angles or lighting angles on the front pane so that there is no noticeable reflection.
So just that for what it's worth. I am by no means an expert. Merely took a digital photography class in high school and have experimented with different lights and lighting etc.
Hope this helped!!
Oh and by the way Koji love the macro work on the insects!!
