Recent research has confirmed that the immune system of fish develops a resistance to the ich organism (University of Georgia, “Immunity to Ichthyophthirius Infections in Fish: A Synopsis”, Dickerson, et. al. 2014 and “Immune Response of Fishes to Ciliates”, Dickerson, et. al. 1996, and Tropical Fish Magazine, February 2014, “Preventing Ich” De-Hai Xu, PhD). Scientists are even trying to develop a vaccine for fish farms. This immunity explains some oddities about ich.
Immunity typically is a very complex response with multiple agents. In fish ich often is found in multiple organisms on just the gills. There are often no visible ich organisms on the skin or fins of the fish. This can be explained by the immune response for the gills being different than the immune response of the skins and fins.
Since mucus would interfere with the oxygen exchange of the gills there is little mucus on the gills. The skin and fins on the other hand have mucus coverings. So these two surfaces would be expected to have different responses to the infectious stage of ich.
Another oddity is that two schools of different fish species in a single aquarium can have marked differences in response to an ich challenge. One school can have all its fish covered with spots while the other school has no spots at all. One fish species just has an inherited immune system better equipped for ich than the other species.
Joey (the King of DYI) infected a clean aquarium of established fish with the ich organism dripping from a net that had been used to unbag new fish. It took thirteen days for the fish to break out into myriad white spots on fish in the second tank . The new fish never exhibited any symptoms. The new fish probably had immunity.
This immunity also explains why some people report fish breaking out with ich when no new fish have been added. A fish with immunity could well harbor latent or dormant cysts kept in check with its immunity. When that immunity drops for some reason, the disease COULD well break out. But we emphasize “could”. Ninety nine percent of the time ich is due to the introduction of new fish without proper quarantine.
Ich in more Depth
Ich is the most common fish disease and warrants a more in-depth discussion. The following chapters are devoted to this common fish disease:
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