Hi jobro, I recently discovered a lump very similar looking to this on one of my plecos fins. Got to know a very knowledgeable guy in regards to ffish health. On asking I was told it was lymphocistitus. There's a lot of speculation as to whether its contagious to other fish. Its possible it is when cysts are visable, from what I found during research. So isolation was recommended despite this. Or speculation about even if catfish can be infected. It is a viral condition, as far as i know there's no cure these lumps come and go and in my case it went as fast as it came, it's back with the others now. I've not seen anything like this since, either on the fish that was affected, or on any others.
"My journey is at an end and the tale is told. The reader who has followed so faithfully and so far, they have the right to ask, what do I bring back? It can be summed up in three words. Concentrate upon Uganda."
Winston Churchill, My African Journey