I thought I replied to this?
Must not have gone through due to my browser problems lately...
Anyway, I shot in an aquarium once. Learned a few things I can pass on...
I shot film when I went because I hadn't gone digital yet. I learned that 100 speed film is all but useless in most displays of the Tennessee aquarium in Chattanooga. Others may have better lighting. I got some decent shots on 400 ISO and 800 ISO film though.
There's a trick to using flash through aquarium glass. First, you need an accessory flash that mounts to the hot shoe. The in camera flash prolly isn't strong enough, and it will be partially blocked using this trick. A hot shoe mounted flash will be more powerful and will not be blocked. The trick is to get a collapseable/extendable rubber lens hood. Most camera shops have them to fit most popular filter sizes. The trick is to extend the rubber hood all the way out and put the front of it flat against the glass. The rubber hood keeps light from the flash from hittin' where the lens "sees". The flexibility of the rubber hood allows you some freedom to move the camera around and get different angles, you just have to be careful and make sure the lens hood isn't visible in the frame. I should note that the glass in some of the displays are not exactly clear and can diffuse and diffract some of the flash through the glass in front of the lens. This reduces contrast in the shot but it's still better than gettin' direct flash bounce back. I have also shot through glass with flash using my hand just like I would the rubber hood and got good results.
Call ahead and find out if tripods are allowed. There are some shots at an aquarium that you simply can't use flash for. Either you can't get close enough to the glass to use the above trick, or you need to shoot at an angle that the hood trick won't work for. In those cases the best thing you can do is use a faster film and maybe a tripod and hope for the best.
Don't use Program or Auto mode if your camera has an Aperture Priority (usually labeled as "Av") mode, especially when shooting the lesser lit displays. In the Program and Auto modes the camera will probably choose a shutter speed too slow and cause you to get camera shake blur, or blurry subjects if they are moving. By using aperture priority mode you can set the aperture wide open, or close to it, so that the camera automatically sets the fastest shutter speed possible for the lighting conditions. This gives you the best chance of freezing the action and getting blur free pics.
Take lots of shots. In less than ideal shooting situations I always stack the odds in my favor as much as possible and shoot as many frames as I can. In bad conditions I may shoot 100 frames or more, end up with 10 really good ones, and maybe 20 that are ok. The rest go to the recycle bin to be cast out into oblivion.
If you're shootin' digital it's a bit tougher unless you have one of the nice digital SLR cameras. The consumer and prosumer digicams have a LOT of noise (digital equivilent to film grain) in the 200-400 ISO range where you'd need to do most of your shooting (again based on the Tenn Aquarium). This is not as big of a problem if you only plan on printing small (no larger than 4 X 6) or sharing via web/email. Downsizing digital files for small prints or web use tends to average out a lot of the noise through the resampling process. There are also programs like Neat Image that can clean up noise very well without obliteratin' detail if you learn how to use 'em properly.
If you have a digital SLR, particularly a Canon Digital Rebel (300D), EOS 10D or EOS 1D (BIG $$$), you can use much higher ISO settings without too much noise. I have owned a 1D and a 10D and both would shoot as high as 1600 ISO with very manageable noise levels. I wish I had gone back and shot the aquarium again while I had those cameras. With the 10D I am confident that I could shoot any shot I wanted at the aquarium without flash.
Most of all, HAVE FUN! I loved the aquarium!
I need to go back one day. Rumor has it that Atlanta is building one soon that is supposed to be incredible. I can't wait to see it if they do. There's just somethin' about water and watchin' the fishies that relaxes me.
I know this is a little late to be of any help to you for this past weekend, but maybe it'll help next time you go.