my goldfish has developed a red spot

Question
one of my goldfish as developed a red spot and kind of bumpy about the size of a dime on her side. she seems fine all functions normal and the other fish have not bothered her. we recently had a had to replaced (it took us a little while to do it)and it showed up during that time. could you please give us your opinion on what it could be.

Answer
Melissa,

 I'm sorry but you recently had to replace what? What size tank is she in and how many other fish are in the tank with her? What are your water perimeters? How often do you do water changes? I need this information in order to help you better.