Cyst-like growth on fish

Question
QUESTION: My comet of 8years has a strange, fairly large growth on its underside, located near its anus and somewhat bilateral. Its behavior seems normal, however I am concerned for the other fish inhabiting our pond. Should I remove the comet and euthanize? Or is this growth a noncontagious form that will not affect the other pond dwellers?

ANSWER: Kehau,

 I would love to help you out. Would it be possible to add a photo of the fish in question? Sometimes the fish just get ulcers but I am not sure if that is what this is. Give me as much information that you can in describing what it looks like, what color it is, if anything is coming out of it. Is there anything in the pond that the fish could have injured himself on? Remember, I cannot see the fish so I need as much information as you can give me. Thank you and I will wait to hear back from you.

---------- FOLLOW-UP ----------

QUESTION: Unfortunately, my camera in not functioning at this time. I can however, give you more details. The growth is definitely internal, the scales and coloration of the fish over the bulge are intact. There is no unusual discharge from the fish or from the area in question. Also I have noticed, since my last correspondence, that the growth, while still predominately  bilateral in appearance, seems to have gotten larger on the left side of the fish.

P.S. Your prompt response and informative response regarding the initial question is impressive! Mahalo Nui Loa!!!

Answer
Kehau,

It sounds like a tumor. These fish get them a lot and unfortunately there really isn't anything you can do. Some people add aquarium salt at a ratio of 1 teaspoon per liter of tank water. This might help the tumor shrink a little but will not make it go away. As long as the tumor is not by any vital organ the fish should be ok. Seeing how the fish is a pond fish, the adding of salt might be a bit difficult. You can either move the fish to your hospital tank or try salt water baths. I hope this has helped and if you have any more questions, don't hesitate to ask.