Before you start for shape the handle you shall cover the blade with tape. To protect the blade and your fingers. I use masking tape that is easy to get of when the knife is finished.
Now start cutting away the wood outside the drawing. If your skilled enough you can start with an ax to do the rough shaping, and then using the knife for the final carving.
When your have cut all the way to the line of your drawing start to round the edges. When your cutting away, specially when rounding the edges you still have to think about a fish. The handle needs to be round and smooth like a small trout in the water.
Here is a film showing how to shape the handle with the ax. Sorry about the camera angle, maybe I need a tripod :-)