Back in 2001/2002 I had a fish that I diagnosed as having tuberculosis. It was a C. euchilus I'd gotten and raised from ~2.5" up to ~5"+ by the time he was really starting to show he had a chronic issue. It was a roller coaster of him getting sick, showing symptoms or not wanting to eat, and trying to get him healthy again.
The cause is bacterial. I forget the name of the medicine that best helped him, but the company that made it went out of business a few years back anyways.
I did best putting him in a tank of his own to make sure he got enough to eat when he would eat. I typically handfed him pellets, soaking them first so they'd soften and squeezing the air out before dropping them right in front of him. He never did recover completely, but he lasted about 9 months once he was in his own tank, so about 1.5-2 years after the initial problems started.