And, I've got a myth that I know everyone has heard:
There is ich in every fish tank
"What utter rubbish" noted Dr. Peter Burgess in Nov 2001's Practical Fishkeeping He studied Ichthyophthirius multifiliis for his Ph.D. thesis topic. Many fish from dealer's tanks are carriers, and if the fish is only lightly infected, the whitespots may not be visible or are only present on the gills of the fish -- not visible from the outside.
The neverending ich myths come about if you do not treat ich to the fullest -- through several lifecycles and with sufficient medications. It is tough since you know the fish aren't happy swimming around in the medications, and you haven't seen whitespots for like 5 days -- but you must keep medicating! That is the only way to completely eliminate it, and then you can put the neverending ich to bed for good. This is especially pertinant since there is at least one commerical medication that claims that ich is gone in 24 hours after adding the medication. This is just plain wrong -- ich has several life cycles and is only vulnerable to medication in one of those stages. Virtually all of the medications lose all of their potency after 24 hours of adding them, so you have to keep redosing so that effective medications are available and all the Ich has a chance to be exposed.
And, as if often noted, a fish may be a carrier for a long period of time (with just one or two protozoa living in the gills) and not break out until stressed. Also, lots of us add a new fish here or there which, if they are also carriers, may push the tank over a critical limit. Makes a good case for quarantining, eh? Two-weeks is not really enough time for ich to go through enough lifecycles so, it is unlikely to know for sure if your newly-bought fish is a carrier or not, for at least a month.
It is important to note that Ich is an organism -- yes, fish can become more suspectible and show more symptoms when stressed, by cooler temperatures, for example. But, if there is no I. multifiliis in the tank, your fish will not get Ich. An othewise healthy carrier host that is stressed may spread it to your other fish, but if there is no Ich in the first place, it is exactly the same problem as when your mother told you if you didn't wear your coat in the winter, you would get a cold. Not wearing a coat can weaken your immune system, making you more susceptible to the cold germs your office-mate is sneezing out, but the act of not wearing a coat alone will not make you sick. Same with ich and stress. Stresses will make the fish more susceptible, but the stresses themselves cannot cause the ich organism to spotaneously appear.
There is no dormant stage, at least that has been found yet, and ich cannot survive if it gets dried out. The dormant ich myth may have came about because of a similar marine ciliate parasite called Cryptocaryon irritans, sometimes called "Ich's marine counterpart." Crypto can remain dormant for up to 30 days, especially at lower temperatures.
The good news is that if a fish survives an ich outbreak, you may notice that it does not seen to be as affected if you have a second outbreak. There is research going on right now looking for an ich vaccine.
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/www.skepticalaquarist.com/docs/health/ich.shtml
