With fish facing away from you, use a sharp, thin-bladed knife to cut along the back of the fish, from tail to head. Make a second cut just behind the gills, down to the backbone.
Holding the knife at a slight angle, cut along the bone to free the back side of the fillet.
Peel back the free meat, then cut fillet away from the rib cage. Turn fish over and repeat above steps for second fillet.