With any moving subject you want to use the fastest shutter speed you can to get the proper exposure. That shutter speed is really dependant upon the maximum aperture, to give you an idea though I've got a Canon 50mm F1.8 lens, with the aperture wide open the best shutter speed I can get at ISO 800 is about 1/60 without a flash. With the aperture opened wide some times it's difficult to tell if blur is from fish movement or because the depth of focus is so shallow at that aperture, more often I'll stop down the lens to F4.0 or smaller (lenses are usually optomized for clarity at F8.0, if I can I try to use F8.0) and use a flash with a shutter speed 1/100 or faster.
I use the pop up flash on my camera with a scrap of white paper covering the flash held in place by a rubber band then set up a remote flash with an optical slave trigger at an angle to the camera and an angle to the aquarium glass, some times it takes a few shots to get the right angles but I've had pretty good results. Depending on the aquarium and the fish some times it's easier to shoot up close with a wide angle lens, other times I've had better luck standing back from the aquarium with a zoom lens.
If you try to use a remote slave with an optical trigger be aware that Canon cameras use a preflash for metering, the preflash will trigger the slave instead of the intended flash that is synced with the shutter. To get around this you'll have to use the FEL button, if your camera doesn't have a FEL function you may not be able to use an optical trigger.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.