[ChuckG]

Here's one I just grabbed on a quick search:

"Put another way, with healthy fish, they can usually produce enough mucous to prevent the ich tomites form getting started on the fish, but once these tomites get a foot hold on a stressed fish, even the healthy fish get overwhelmed."

Hmmm - guess I just contradicted myself again.

That was from: Aquarium Ich: Ichthyophthirius multifilis and Cryptocaryon irritans treatment, identification, and life cycle.

OK - I give up.

A Healthy fish may very well carry ich but show no symptoms.