poikilotherm
Aquarium Advice Activist
I like thinking about this stuff, and as this thread is moving towards the "compromise" that I believe is where the truth lies, I'll chip in with my 2 cents. I am a student of Microbial Ecology, and I don't claim to have any special insight because of this, but I enjoy thinking about this stuff.
To go to the bacterial analogy, yes there are bacteria present on skin and mucosal surfaces that protect that surface from invasion by pathogens. The pathogens are often present, but cannot invade unless the normal flora is wiped out (antibiotics, antibacterial soap, pH change, etc) or if there is an injury to the surface allowing bacteria under the skin.
The case of Ich is somewhat different, as there is no real analog to the protective role of normal bacterial flora that I am aware of in the protozoan world.
There are published studies regarding the production of antibodies in some fish (e.g. channel catfish) that render them immune to Ich. Another study showed that the parasite has been found in the abdominal and intestinal cavities of fish. Another article I found suggests that immune fish in the same tank as susceptible fish can have a protective effect on the susceptible fish. The plot thickens. I can post these references if you are interested, and should be able to get the articles as PDF's if you're really interested.
An argument that has been made against latency is that you would be able to see the trophont stage of the organism. I believe that latent Ich is common, but perhaps not universal. The discovery of Ichthyophthirius multifiliis in the tissues surrounding internal body cavities provides an interesting candidate for how latency can persist undetected for long periods. Either way, fish with compromised immune systems are clearly the ones who suffer the full brunt of the disease, and other fish have varying degrees of resistance.
To go to the bacterial analogy, yes there are bacteria present on skin and mucosal surfaces that protect that surface from invasion by pathogens. The pathogens are often present, but cannot invade unless the normal flora is wiped out (antibiotics, antibacterial soap, pH change, etc) or if there is an injury to the surface allowing bacteria under the skin.
The case of Ich is somewhat different, as there is no real analog to the protective role of normal bacterial flora that I am aware of in the protozoan world.
There are published studies regarding the production of antibodies in some fish (e.g. channel catfish) that render them immune to Ich. Another study showed that the parasite has been found in the abdominal and intestinal cavities of fish. Another article I found suggests that immune fish in the same tank as susceptible fish can have a protective effect on the susceptible fish. The plot thickens. I can post these references if you are interested, and should be able to get the articles as PDF's if you're really interested.
An argument that has been made against latency is that you would be able to see the trophont stage of the organism. I believe that latent Ich is common, but perhaps not universal. The discovery of Ichthyophthirius multifiliis in the tissues surrounding internal body cavities provides an interesting candidate for how latency can persist undetected for long periods. Either way, fish with compromised immune systems are clearly the ones who suffer the full brunt of the disease, and other fish have varying degrees of resistance.
