Hey everyone, Im a first time poster here, and Im posting because one of my fish has a large grown on the top of his tail. It started about 4 months ago and has been growing ever since. There are 6 other fish in the tank and none show any signs of similar problems. It is a Praecox rainbow fish about 3 years old. I have attached some pictures, any help as to what it is or what I should do would be great!.
Bryn
Bryn