No sources to offer but from personal experience i believe more species do infact hold a better resistance to Tb.
I had a batch of dwarf neon rainbow fish about 2 or 3 years ago which had the dreaded tb infection. I did my best to treat them but we cant get the right meds here in the uk unless prescribed by a vet . I lost them one by one over a 9 month period but the 8 cories they were in the tank with had no ill effect from the infection and all of them are still alive and well to this day.
Most of the fish from Asia, South America and Europe have been around for a lot longer than some species like Rainbow fish. You probably talking 100,000+ years, and have been exposed to Mycobacteria since they have been around. Whereas rainbow fish (newer species) never evolved with Mycobacteria so dont show the same resistance.
Yeah I've heard of rainbow fish being notorious for dying due to TB, it makes sense that resistance would be an evolutionary trait in older species. It would be a good study to conduct if anyone had the scientific knowhow or money haha. I might look for scientific journals later to see if there's any formal sources to back it up
I've heard some people propose bottom feeders don't generally get ill effects because they spend a lot of time sifting through waste and therefore don't develop the adverse symptoms consistent with other species. Whether that's true or not remains to be seen but the generally hardiness of most catfish species would be concurrent with that.
Myco is a very interesting topic to me because of how it operates. A recent article suggested that fish can be carriers with the mycobacterium remaining dormant (something which aligns with the resistance in older species). Its also been posited that a majority of dropsy cases in bettas are cause by myco which is what causes their immuno collapse. It would explain why unstressed fish die from it so easily, their immune systems aren't "on alert" so to speak which is why they spiral very quickly once they show symptoms. Although, I firmly believe overbreeding of bettas also contributes to their predisposition.
All of this is speculation on my part, but interesting nonetheless. Fish are illusive when it comes to diseases and it can be hard to both diagnose and understand how they operate. I wish aquatic vets were more widely available haha.
