Completely removing the backbone of an odd-shaped fish like a flounder sounds like an impossible task, but Vern Becnel has mastered it.
In addition to a narrow-bladed knife, he uses a pair of stainless steel toe nail snips that can be purchased at any drug store.
Try this; it is easier than it looks.
1) After de-heading and gutting the flounder, make a cut to the backbone the length of the fish down the center line of the dark side of the fish.
2) Turning the knife sideways, cut the flesh loose from the backbone, starting at the incision and working toward the edge of the fish.
3) Turn the loosened flap out of the way and repeat the process of cutting the flesh loose from the backbone on the other side of the fish.
4) After folding both flaps aside for better vision, insert the knife beneath the backbone of the fish and above the flesh on the bottom of the fish. Cut in both directions as far to the edges as possible and as deep as the knife will go to loosen the backbone from the flesh.
5) Use the toe nail snips to cut the ends of the backbone loose from one side of the fish.
6) Lifting the free side of the backbone and using a knife, finish trimming any flesh loose that is still attached to the backbone.
7) Use the toe nail snips to free the remaining side of the backbone.
8) With both sides of the backbone free, cut it loose from the fish at the base of the tail. The boneless flounder is now ready for stuffing.