While Lee's piece is mostly correct, there are a few clarifications that need to be made.
2. Only time a human can see this parasite with the naked eye is when it is ‘pregnant’ on the fish and has formed a white nodule. (The white spot is about the size of a grain of table salt or sugar).
It's important to note that even when the parasite is on the fish, it's at the lower end of what you can resolve with your naked eye. If you have good eyesight and it's on a dark colored fish, you might be able to see the parasite itself. The white spots typically associated with the disease are not the parasite itself, but the displaced tissue around where the parasite is embedded. As Lee mentions later on, getting rid of the white spots does not cure the disease.
14. INTERESTING FIND: If no new MI is introduce into an infected aquarium, the MI already there continues to cycle through multiple generations until about 10 to 11 months when the MI has ‘worn itself out’ and becomes less infective. A tank can be free of an MI infestation if it is never exposed to new MI parasites for over 11 months.
This study has been pointed out twice in this thread now, bit it's important to not that it was only one study using one method. Other researchers have maintained viable cultures for longer using different methods. While Burgess and Matthews' work is noteworthy an may very well be correct that pure lines die out after 10-11 months, this hasn't been independently confirmed. If you don't add anything new to the tank for 10-11 months, there's a good chance any ich will have died off, but it's not something hobbyists should bet on.
3. No fish, no matter how good its defense is, can stop being infected. A healthy fish will and can be equally infected as a sick or stressed fish...
4. A weak, stressed, or sick fish will die sooner than a healthy fish, but is no more likely to get infected than the healthy fish.
Actually in the studies on immunity, no parasites were found in examinations of a few fish following challenge with the parasite. That suggests that some fish may in fact have completely stopped the parasite from infecting. Also, it's known that the immune system can be suppressed by stress or illness, so it's not accurate to say that a sick fish is no more likely to be infected than an otherwise healthy one, which he goes on to say later.
I think the point Lee was trying to make in #3 though was that making sure fish are otherwise healthy will not guarantee that they can fight off the parasite or that they won't get it as badly if they do get it. That part is true. #4 is one of the few places I think he's gone way beyond what's reasonably inferred from the literature.
An immune fish doesn’t remain immune. Separated from the disease for months, the once immune fish can become MI infected.
While some authors have suggested that this is a possiblity, I haven't seen any studies showing it to be true. The only studies I know of that looked at how long immunity was maintained showed that it was still effective
at least 6 months following initial infection. They didn't test it on any longer periods of time to see if there is some point at which it's lost.
It goes away on its own. Untrue.
I think the point he's making here is that in most cases, even after the spots disappear after the initial infection, the parasite hasn't been eradicated. Even fish with immunity still usually harbor a few or the parasites, so you're unlikely to see white spots even though the parasite it still there. However, as I mentioned earlier, there have been some cases where pathology exams failed to turn up any parasites after the second challenge, so in some cases the ich may in fact have gone away on its own- but only for that fish. Any other fish that haven't developed total immunity may still be infected.
13. If the MI can't always be detected, then why bother with a quarantine procedure? In the confines of a small quarantine and being there for no less than 6 weeks, the MI parasite will make itself known because the fish is weakened and the fish can't get away from being re-infected by multiplying MI parasites. In other words, the quarantine procedure instigates a 'bloom' of the parasite which will make it visible to the aquarist.
This is a matter of conjecture, and personally I disagree with it. Fish that have already developed immunity (say at the LFS) are still likely to harbor small numbers of parasites, which may not be visible. Even a small number of them can reproduce to become thousands of theronts within a single cycle, BUT even under ideal conditions (for the parasite), with naive fish in small, isolated tanks, only 5-20% of theronts successfully infect a host. With a potential host that already has partial immunity, Burgess and Matthews showed that success drops to about 0.05%, so there's no reason to assume that you will get a "bloom." For example, Burgess and Matthews found that fish that had been exposed to only 200 theronts before only hosted an average of 13 parasites after their second exposure. Other work shows that a single tomont can produces at most, 1030 theronts (only about 200-300 max for most strains). That means that even if you assume the lowest level of immunity and the maximum number of theronts from one tomont, those 13 parasites give you about 7 on the next cycle- a decline in numbers, not a bloom. You have to weaken the fish enough to double the success rate of infection just to keep a stable number of parasites. The potential problem comes when you then add that fish to the tank where there are fish who have never been exposed to ich before or may have lost their immunity over time.
