Last year, this lady used to live next door had a goldfish that she didn't wan't, and I said I might take it, I just wanted to inspect it and quarantine it first. Instead, she came into the yard when we weren't home and dumped the fish in the pond without telling me. The fish looked healthy at first, but now it looks like the fish has a rather large tumor on it's back' right above it's head. I don't think I can get any good pictures of it since the fish is at the bottom of the pond, but I might bring the fish in and put it in a spare 40 gallon tank. How should I go about threating it? I'm thinking if it's cancerous, I might just have to euthanize the fish. I have never had a fish with a tumor before.