Well thanks for letting me know they cant be immune, but as ich has been present from about 4 years ago in my tank when some of them had it I haven't seen it pop up since a fish addition 3 years ago. So if there not immune now I wonder why then they haven't shown any signs of it? Whatever the reason a built up immunity or not something is helping them not get reinfected with it. If it's true they cant have immunity then what could be the reason for no signs of it in 3 years? The ich has 13 fish to choose from in my tank from a blenny to 3 tangs, 4 triggers, couple of clowns, a wrasse etc. If they have an immune system, then I would naturally think they are now immune.
@Paul B any opinion on fish immunity possible?