...didn't know if possible I thought it only occured in Salmonids? Anyone? Anyway, here is my situation. Spartan, one of my best goldfish recently developed what appeared to be a case of constipation. I fasted and fed skinned peas which produced a little poo, but not the cleansing which I has hoped for. Then I noticed that the swelling was not symetrical. He seemd to eat and swim normally, just occasionaly resting on the bottom. I continued to sparringly feed peas. Then just last night I noticed he was spinning violently around the tank...exactly like this... [YT]http://www.youtube.com/watch?v=tLirWEFLIV0[/YT] http://www.youtube.com/watch?v=tLirWEFLIV0 ...except in my case he seems bent and cannot straighten out. I immediately put him in a clean 10gal quarrantine tank...he is about 5-6 inches of common goldie. I added a bubble stone, and Whisper 20 filter for aeration/filtration. This was at midnight last night. This morning I ran out to petsmart and picked up some marycin II and began treatment. I figure if it is not a tumor, It might be an internal bacterial infection. I don't know how it would have just come on since nothing has changed in the tank for months (5+). I'll see if this helps, if not I'll probably have to euthanize. I'll try and get pics. His detrioation only took a matter of a couple of days. Should I add some aquarium salt? if so how much? - No pineconeing - asymetrical swelling in belly/gut - curved spine - spinning while trying to swim - Water tests are good. Side note...he was in a tank with my other 3 goldies...they have lived together for as long as I've had them. Should I clean their tank, and treat them..even though they currently show no signs? Or just watch them closely? This sudden unexplained illness just bugs me. helpless etc. Thanks for the help...any help.