Question
We've had this fish for nearly six years in a 100 gallon pond with, at the moment, three other smaller goldfish varieties.  Last summer something got to the fish (we suspect a neighbor's cat).  One was completely missing, one left outside the pond, dead, and our largest one, alive in the pond but with a gash on it's side. It didn't seem to be deep.  We have now noticed a tumor developing on this side, and it also seems as if there is another one starting on it's other side.  Other than that it appears to be OK, swims well and eats.  Suggestions please -  should I remove this fish, or just leave alone ?  Thanks

Answer
Dear Elfrieda,

Thank you for your question and sorry to hear this news.
It is hard to tell from A distance, however I think the "tumor" might be the result of the wound and it then should not be A tumor however more something like bacteria and wound dirt.
The best way (if temperatures are ok) to place the fish in A quarantine tank and to check it closely.
Normally we work following:
check water quality
check fish on visual abnormalities
check scrapes from the fish under A microscope for parasites, fungus, etc.
Clean the wound with cleaner
Rinse the wound
disinfect the wound
cover with anti bacterial product
cover with water resistant coating

Monitor the fish and do not feed for the first days.

These products are available in the better fish stores.

When not available you can use the "red" disinfection (we call it Isobetadine) and then cover the wound with propolis.

Good luck!
Keep me posted if I can be of assistance please!

Kind regards,
Raf