1. Roll a piece of fondant into a 1" long log shape, then flatten into an oval.
2. Use a triangle cutter to cut a deep "V" in the center of the oval.
3. Use your fingers to pinch together the right and left sides of the oval.
4. Set aside to dry.
5. For the fin, use the circle cutter to cut out fondant, smoothing edges with your finger as necessary. Stick to the side of the cake starting from the top, overlapping the circles to create scales.