Bake cupcakes per recipe and cool completely. These would be nice if you did them in different colored cupcake liners and then you could match them up with the colored M & M's. You may even want to use these Fish Themed Cupcake liners.
Pipe the buttercream frosting on each cupcake in a smooth, flat swirl. You may want to practice first so you get it right.
Sort the M & M's into colors, that is, if you want them the look like ours, but experiment and see how you like them best. Then begin laying down the M & M’s on one side of the cupcake, allow them to overlap just a little. There really is no right or wrong way to do them.
Leave an oval shape section uncovered on the opposite side of the cupcake so you can add a face of the fish to it.
Place a sugar eye on the face and squeeze a little colored frosting to make a mouth.
Add the rainbow candy tail on the back of the fish, wide side out, so it looks like the fishes tail fin.