Myco is incurable. It survives bleach. If a human, like the one writing here, catches it from a fish, it takes an antibiotic cocktail for close to six months to kill it off. It is one tough pathogen.
And so, when it breaks loose, you are scr^^^ed. I assume that every farmed fish I buy has it. In most cases, it is a slow thing that shortens the lifespans of fish and never gets virulent. It becomes a chronic killer.
It can break out and kill very quickly, if fish are run down, old or sick. It isn't always slow.
It is also a taboo subject. On other forums, people posted photos of fish with the rectangular oozing lesions that the disease sometimes produces (having caught it, I learned about it). If anyone dared say fish tb, or Myco, they could lose their heads. There is an aggressive urge to deny this disease in pet stores and in the industry. In discussion with Asian fish farmers (Asia only matters here for climate, and because it's the biggest source of farmed fish), some have said a very high percentage of the fish tested were carrying it - well more than half. But it's chronic so it isn't their worry, except when outbreaks wipe out a pond.
Transfer to humans is rare - very rare (lucky me) - but it scares people. Cats are way more dangerous to us than fish (cook them well, werewolves), when it comes to diseases. In the pre-antibiotic era, human tb killed millions, and those two letters (tb) frighten people.
