OK. I am going to break this down, and hopefully end the mass hysteria that seems to be going on. First, I would like to say, I am a Medical Technologist. I am currently a laboratory supervisor with many years of Laboratory experience. I am not a self proclaimed basement breeding fish expert.
99% of fish have some form of pathogen, whether it be Ich, Myco, or other.
Most fish is a well kept aquarium do not get sick. Healthy immune systems fight off illness. Think of this in terms of a chemo patient. They can died from the common cold because they're immune system is weak and stressed. Most healthy people shrug off the common cold.
I am a woman. I have yeast. Doesn't mean I have a yeast infection. Oh wait, I also have staph on my skin. Doesnt mean I have a staph infection. Oh and that yogurt you are eating? Oh that has bacteria in it too. Lactobacillus, which is also known as normal vaginal flora. Oh yes, it is. Think about it.
Everyone and everything has a bacterial subsystem living within them, each one keeping another in check. It is all part of the immune system. When one part gets compromised, defenses fail and you end up diseased, This goes the same for any organism, whether a mammal or fish.
HEALTHY TANKS EQUAL HEALTHY FISH. IF YOU ARE CONCERNED, QUARANTINE. TAKE CARE OF YOUR TANK.
** 75g: 2 Green Terrors, 2 Severums, 3 Synodontis Eupteras ** 75g: 8 Yellow Labs, 11 Blue Zebras, 7 Hap. sp35 ** 55g: Jack Dempsey Breeding pair