Hi George,
That is en excellent question! I actually use the technique you described in your question to allow me to get closer to fish than if I were to have my camera right against my mask. It is a little challenging for me because I shoot with a housed SLR underwater cameraToday's underwater point and shoot digital cameras with their LCD preview screens allow you to get the camera way out in front of you keeping the mass of your body, and most importantly your bubbles an extra distance from the fish.
Another thing to try when shooting fish is to begin learning how to get a feel for if a fish will stick around for its portrait. This takes some time and practice but is well worth it as you will become more selective of which fish to spend time with and when to move on instead of wasting precious bottom time.
Hope this helps!