Need input on sick fish
All 20 of my Koi and other fish came through winter well but today I see a lump on my 8 year old orange Koi. I look over my fish all the time but never saw this till now. Its about the size of a quarter and 1/8 high about 2 inches forward of the base of the tail on her one side. Her scales are raised over the bump. I see no other issues or discoloration any ware on her and her behavior is quite normal.
Has anyone seen this before or have an idea what it maybe? Tumor or maybe a parasite. I don't know if I should treat her or cull before it moves to the other fish.
Any input will be appreciated.