Plenty of people love to film and scuba dive at the same time. Some people even opt to have head mounted cameras so that they can keep their arms free whilst diving, however this can cause other issues with the quality of the shot captured.
When scuba diving and filming at the same time it is easy to make the image on the camera "jolty". By using a wide angle Lens you can improve the stability of the video plus have more of chance of capturing the fish on film simply by increasing the field of vision.
The down side of using a wide angle lens is that the subject will appear further away and smaller that it actually is.
This short clip shows the difference between the two. The fish in this clip are really quiet large.