Captain Jim, I am leaning towards that... maybe he just grew too big too fast...
I did a cursory exam and did not notice anything..and parasites usually take much longer.. bacterial usually a few days or Sx show.
this was just WHAM...
I worry about my Altum.. they are the 'dream' fish for me.
after looking for cause (turned out a contributing factor was a neighbors child visiting my Grand daughters).
I did some research and suspected Hex as another contributing factor. I discovered one way to kill hex is to raise the temp of the tank to 90f for 1-2 weeks.. this does not fix hex internal on the fish but will kill the next phase.. hex will shed in about 1 week into the tank water.
I normally keep my altum at 84-86 but noticed that the temp felt a bit cool I tested with 2 more thermometers and discovered the tank had dropped to 80..considered cool for Altum..I suspect this may have stressed the Altum so slowly raised the temp to 88(lower end of the temp threshold for the hex but easily tolerated by Altum.. within 2 weeks all appetites have returned to normal as well as the coloration of the Altum.
the culprit for the heat loss.. failing stealth heater.. added a jeager and replaced the stealth.