Am making a fish out of a ball of styrofoam to use on the top of the cake. Didn't need the extra cake and figured that way I could make it early. Should I cover it with fondant first before piping? I was going to cover with royal icing and fondant fins.

Sounds crazy but think it will work? Any suggestions appreciated!

You do not need both.....one or the other as long as you are completely covering it.