I don't know if some fishes are more susceptible than others. I think they
all may be susceptible, it just depends on the amount of time fishes are
exposed to it. I've seen it in a variety of fishes...cichlids, tetras,
bettas, goldfish.
In closed systems such as our aquaria, the numbers of mycobacteria can
increase to the point that the fish is overwhelmed.
A reminder: To my knowledge there is no mycobacteria specific for fish.
They are just there in the environment. You can get from peat moss,
swimming in coastal waters, walking through a swamp. In hospitals, it's
been found growing on medical equipment.
The National Aquarium at Baltimore veterinarians recommend the alcohol as
they found that chlorine did not kill mycobacteria. They use chlorine to
remove/oxidize organic material to assure the alcohol contacts all
mycobacteria in/on the tank.
An excellent article on mycobacteria is found in _Clinical Microbiology
Reviews_, April 1996, "Epidemiology of Infection by Nontuberculous
Mycobacteria" by J. Falkinham III.
Denise