1. Spoon 1/2 cup of the vanilla frosting into a small Ziploc bag, press out the excess air, seal, and set aside. Tint the remaining can of vanilla frosting pale blue with a few drops of the blue food coloring. Cover and set aside.
2. For the fins, place 24 of the circus peanuts on their sides and cut lengthwise into 2 slices, to make 48 slices. Lay each slice cut side down and cut each in half on the diagonal to make 96 pieces. For the bodies, place the remaining 24 circus peanuts flat side down and make a diagonal cut from one end, removing no more than 1/4 inch.
3. Spread the tops of the cupcakes with the light blue frosting and smooth. Place 1 of the circus peanut bodies on top of each frosted cupcake. Arrange fins, cut side up and pointed ends out, 2 at the uncut end of each circus peanut body and 2 on either side in the middle.
4. Snip a small (1/8-inch) corner from the bag with the vanilla frosting. Pipe a large dot of frosting at the cut end of the circus peanut body. Press 2 orange candies into the dot of frosting for the eyes and 1 cereal O for the mouth. Pipe small dots of vanilla frosting on the orange candies and add the brown candies for the pupils. Repeat on all of the koi bodies with the remaining frosting and candies.
5. If you like, arrange the cupcakes on a surface with circles cut from white and blue papers and sprinkle the platter with white and light blue candies.