I'm not sure who suggested me, but I think you should try messaging Sakura8 if you are wanting to try and treat him. I am not actually all that good with diseases and treatments.
However, if he is really suffering and you think it is going to be crueler to try and treat rather than euthanise, I would advise euthanasia.
I am not one to let fish or any of my pets die 'naturally', as rarely are natural deaths very peaceful.
There are several methods of euthanasia. Blunt force trauma is the quickest but understandably hard for a lot of owners. You can use clove oil as well, but I found that this tended to take a while and was not always an easy death. The method I use is to put a container of water in the freezer and wait until the surface freezes over. I smash the ice, remove it from the container and put the fish in. It is usually over in seconds, and none of my fish have ever thrashed about excessively or looked like they were in extreme distress.
Hey LBF..i am in need of some help i was told yu may be able to help i have a VT that may have Lymphsistis..and im not sure if I shuld put him down or wait it out..its only been a week or so..but he cannot eat..and struggles to breathe..what do yu suggest,?