Nice shots, great shoal. See if your camera has manual settings and if it does, turn down the aperture (they'll call it AE, or F stop or whatever) as low as you can and try some more shots. This will bring up the shutter speed and let you lose the blur. If you can't do that, set your camera to portrait mode and it should do something similar. If that still doesn't work, you might need to increase the light a little bit to get really crisp shots, things like a shelf light pointing down in the tank will help a little, or if you can find an extra fluorescent strip lying around (not always possible though) put that over the tank. Your shots seem good, the only issue is that the shutter speed is a bit low, if you can bring that up you'll be good.