You are getting quite a lot of reflection happening on the glass.
Either locate the flash remote from the camera and ensure the angle is such that the light doesn't reflect directly into the camera, or angle the camera on the glass so that the light wont reflect back to itself.
tried to angle it as much as i could. When i turned the flash off, the fish looked a lot more blurry. I'm going to try to take a few soon with all the light soff except the one directly over the tank.