A common myth that goes along with the marine reef aquarium hobby is that cleaner shrimp will cure a fish of ich.  Here is what a fellow member of Reefcentral had to say about this.  A big thanks to “GreenBean” for his explanation:  

   “There is no evidence that any cleaner species eats ich in any real number, either in the wild or captivity. It’s never been found in the gut of cleaners in the wild and in lab tests cleaners have never been shown to make a significant difference on parasite loads. The ich parasite is under the skin of the host and without harming the host fish, the cleaner only has access to the parasite for about the 5 minutes that it takes for the parasite to burrow through. Because that 5 minutes occurs in the wee hours of the morning, cleaners will never naturally encounter the parasite during that time. In the lab, even when cleaners were induced to clean during the period when the parasite was burrowing in, they ate very few of them and made no significant difference in the parasite loads of the fish. The white spots associated with ich are only damaged skin due to the parasite underneath and guess what a large part of the diet of most cleaners is…. dead skin and fish mucus. Picking off the spots doesn’t cure the fish.”