How should I photograph a fish in motion?
Various techniques can be used when photographing fish that are not standing still. You might consider training on a Grouper fish to begin with, since it has a habit of swimming slowly and never seems to be in a hurry, as long as you don't make any sudden moves or come to close, thereby scaring it away.
Start by observing the fish movements for a period of time. When you do this, you might be able to predict its habits and venture an opinion what path it usually takes and where it may make its "rest stops". Fish usually move in a specific pattern between the path and that spot. This pattern of behavior is quite common in fish and understanding it is the first step to getting good photographic results. Once you understand the grouper's characteristic movements, you can decide where on its travels you wish to photograph it.
To start off, you will want to stay quite far away from the fish and hold the camera with your arms extended in front. Advance slowly with the camera extended to avoid startling the fish. When you arrive at the spot from which you would like to take the picture, aim the camera, press the shutter button halfway until the camera is in focus. Wait for the fish to come along. When the fish arrives at the spot you wish to photograph, immediately press the shutter button all the way.
It is very important that you focus on the area first [by pressing the shutter release button halfway]. Failing to do so will result with blurred images and the fish might no longer be in the frame. The shutter will not activate until the camera has had managed to focus and calibrate exposure and white balance settings. The shutter lag may be as long as 1 second. Pushing the shutter release halfway reduces the shutter time lag, thereby minimizing the chance that you will end up capturing an image of the tail of the fish.
Some cameras feature manual settings as well. If it is possible to set the shutter speed on your camera, you might consider choosing higher shutter speeds in order to avoid blurred images in which the movement of the fish has been captured.