alright, since my credibility is being questioned, read it yourselves.
from wetweb
http://www.wetwebmedia.com/labroide.htm
peer-reviewed journal
http://www.jstor.org/pss/3505553
wiki
http://en.wikipedia.org/wiki/Cleaner_fish
It was noted on RC and other sources that it is unlikely that these wrasses are getting all the nutrition they need from prepared foods, thus leading to their eventual demise. Two years is not long term.
you guys are basically missing (or worse, ignoring?) my main point entirely. Let's say for argument's sake that these fish were as hardy as damsels and didn't have the abysmal death rate it currently sees in this trade. It should not have been removed from the ocean in the FIRST place. These species serve a vital role in the ocean. That's why you see lines of fish waiting at a cleaner wrasse's cleaning station. That's why you see these fish, completely unafraid of large predators like groupers, swimming around inside of their mouths picking at parasites. That's why said large predators choose to be cleaned over getting an easy meal. If they weren't such an important fish on the reefs, they would get eaten quickly after venturing in to see what shark teeth look like out of curiosity. Each cleaner wrasse station is a high demand function that serves a broad area (evidenced by lines of fish waiting their turn). Take away that fish and you remove this function from said broad area, depriving hundreds of wild fish of their parasite removal. Why? So you can save a handful of fish in a glass box.
And an interesting tidbit: they don't even eat ich. A study done by Alexandra Grutter, Parasite removal rates by the cleaner wrasse Labroides dimidiatus, 1996, examined stomach content and none of the fish stomachs they found contained ich. 99.7% +/- .06% was gnathid isopods, the rest were caligid and other parasitic copepods. None were cryptocaryon (a ciliate protozoan). I could see them taking ich ectoparasites in captivity (considering there's nothing else for them to eat) but would it be enough for them either nutritionally or in sheer volume? imo, no, not unless you have a full load of fish in a 1000g tank.
Another factor to consider: would it have any real impact on ich in the tank? imo no. They'll eat the ectoparasites but ich burrows under fish scales and cannot be eaten then, nor will they be eaten in their planktonic forms or in their cyst stage in the sand. The ectoparasitic stage of ich is shortlived. They will live in the sand damn nearly indefinitely (i think it was Eric Borneman who found this out by observations of a fishless tank) so you'll basically never actually get rid of the damn things.
A better approach is other cleaners like neon gobies and cleaner shrimp, which although I understand they are hit or miss on cleaning, at least they eat other things . If you didn't stock such that you can accommodate them, tough chickens. The other solution is to not let your fish get ich. QT. Dip. Choose livestock not known to be prone to death/infection. Be proactive, not reactive (generally a good rule of thumb in this hobby).