For more generous-looking helpings keep the top and bottom fillets whole. This technique requires more practice than the technique for making 4 fillets.
Cut the head behind the gills and remove. Make a slit across the tail end and slice around the edge of the flesh where it meets the fins. Insert the knife flat along the backbone between the rib bones and flesh. Use a sawing motion to cut to one side, keeping the knife flat.
Take the knife back to the backbone and repeat on the other side, making 1 large fillet. To make the second fillet, turn the fish over and use the same procedure on the other side.