wart?

Question
Hi Chris,
I was wondering if you could help me again!  I have some goldfish that are probably about 5-7 years old.  They are the kind that you can put in a pond, but I keep them in a "pond" fish tank at school (I'm a high school biology teacher).  They have been fine, healthy etc.  The tank has live plants in it, an oxygen bubbler and I vaccuum the tank.  Occasionally this brown algae will grow on the sides of the tank (50 gallon) and I wipe it off.
The question I have is, on one of the fish, right next to his dorsal fin, is this thing that looks like a wart.  It has now grown in size to about the size of a pencil eraser.  I don't notice any difference in eating or behavior.  The other fish seems normal.  The color of the wart is gold, just like the surrounding area of the fish.
What is it?  What can I do about it?  Is there need to worry?
Thanks!
Rebekah

Answer
Hi Rebekah;

Glad to hear from you again!

Sounds like a wart to me too. If it was a weird color like brown or black I would think cancer or something. There really isn't anything you could do about it anyway if it is cancer, but at least it isn't contagious to the other fish.

Followups welcome

At Your Service;
Chris Robbins