Minus two northern brothers.
When we lost our umbee,
duanes
suggested it was columnaris. The swelling and behavioral symptoms of these two bullheads were superficially similar, as was the timing too.
So if I had to guess, I'd say columnaris.
We had had them for roughly 2.5 years staring from 1.5" in a 240 gal and their final measures were 12.5" and 13.5".
Good tank mates, never noted to cause any problems.
They weren't that fat or swollen at all before they got sick but rather fit.
First to go:
Second a few days later: