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All of this was culled from the scientific literature. It seemed worthwhile to look for actual peer reviewed, scientific facts about ich rather than just rely on the anecdotal knowledge that gets passed around through various aquarium sites. This is just a fraction of the stuff I came up with:

(1) What we call "ich" or "ick" is not actually ich - which refers to the freshwater parasite. What we are actually referring to is Cryptocaryon irritans ("ich') or Oodinium ("Marine Velvet"). The freshwater parasite is actually only distantly related.

(2) There are at least four different genetically distinct strains of Cryptocaryon irritans and they are prone to something called "founder effect" where they can become distinct from earlier populations if cut off from them.

(3) Some of the aquarist literature claims that Cryptocaryon and Oodinium are rare in the wild and while they do occur, fish almost never die due to these diseases. This is because the fish are spaced so far apart and the currents are strong enough that it is hard for the parasite to find another host before it dies in the free-floating stage. However, there has been some more recent articles that state that it is possibly more frequent in the wild than previously thought - but the infections are not as severe and it is rarely a cause of death.

(4) There have been studies on single species of fish that have used some interesting treatments. A group in Florida treated red snapper at fisheries for Cryptocaryon using a combination of hypERsalinity and quinine based drugs (what humans take for malaria) with a 100% success rate. A Japan group used cow lactoferrin (the hormone that produces milk in cows) and caprylic acid (in separate studies) given orally to a group of sea bream to treat Cryptocaryon infection and also had 100% success rate.

(5) While Cryptocaryon is non-specific (meaning it will pretty much infect any fish), the progression of the disease at different temperatures varies depending on what species is infected. In one study that I read, temperature had no effect at all in the progression of the disease in one fish, higher temperatures were more beneficial to another fish and lower temperatures were more beneficial to the third species.

(6) Hyposalinity absolutely does work as it messes up the balance between the protozoan and its environment. If you drop the salinity enough, the parasite will actually explode in its free floating state. In order to have this happen to 100%, you have to drop the salinity to the equivalent of 50% natural sea water and 50% fresh water. Unless of course you have a strain of Cryptocaryon that is adapted to estuarine conditions (of which there is at least one strain). In the case, you would need to drop the salinity further. You can kill Cryptocaryon with higher salinities but it will take long. At anything less OR more than normal salinities, the Cryptocaryon parasite did not grow and develop normally.

(7) Fish CAN become immune to Cryptocaryon infections and that immunity seems to last about 6 months, unless there is repeated exposure. This was tested experimentally separately in the thick-lipped mullet and mummichogs, but I think would could extrapolate those results to other fish in our reef tanks.

There have been a lot fewer controlled studies done on Marine Velvet - I'll have to see what else I can dig up earlier. I just thought that some of this might be of interest to people, considering the prevalance of threads on "ich" here.
 
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Pedro Nuno Ferreira

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Hi ellebelle;-)

Excellent subject you bring here and excellent data gathering. If you could post the sources, it would be very good to.

ellebelle said:
(2) There are at least four different genetically distinct strains of Cryptocaryon irritans and they are prone to something called "founder effect" where they can become distinct from earlier populations if cut off from them.

This can mean that like virus and bacteria Cryptocarion irritans can evolve constantly and addapt, which may rapidly render non effective some medications/treatments.

ellebelle said:
(6) Hyposalinity absolutely does work as it messes up the balance between the protozoan and its environment. If you drop the salinity enough, the parasite will actually explode in its free floating state. In order to have this happen to 100%, you have to drop the salinity to the equivalent of 50% natural sea water and 50% fresh water. Unless of course you have a strain of Cryptocaryon that is adapted to estuarine conditions (of which there is at least one strain).

Hypo salinity is in fact a good approach to eliminate Cryptocaryon but the fact that is causes it to explode (lyse) leads to think that the osmoregulation in this organism operates in the sense of removing excess water from the body fluids because they have higher salinity levels than the surrounding environment fluids which causes the organism to absorb water and thus burst/explode if the osmoregulation system is out of action and this is the oposite of what happens at least with marine fish (Hyposmotic) that tend to loose water to the surrounding environment as it has higher salinity levels than its body fluids (the oposite happens with fresh water fishes - Hyperosmotic), Osmoregulation in fish - Charles Delbeek

I found also these interesting relevant links

Complete article - Some characteristics of host-parasite relationship for Cryptocaryon irritans isolated from South China
Activity of the antimicrobial polypeptide piscidin 2 against fish ectoparasites


Hyposalinity Treatment

C. irritans is a ciliate protozoan found in sea water and it has a number of stages in its life cycle. Infective stages burrow into the skin and gills of the fish and form a protective outer covering of skin. Here they feed on tissue fluids and skin and grow. When mature, the parasite breaks out of the cyst and after some time as a free-swimming form encysts on any suitable substrate such as the sand or rocks and divides many times to produce the infective forms (Colorni, 1987). The infective forms must find a suitable host or they will die.
The total time from the mature parasite detatching from the fish and reinfection of the fish is about 2 weeks at normal tank temperatures. This is why "Ich" may appear to clear up but then comes back a a week or so later but a lot worse.
The low salinity causes the most of the tomonts to rupture, killing them
Marine teleost fish (higher bony fishes) maintain their osmotic concentration at about one quarter to one third that of sea water. In normal sea water, these fish have a tendency to lose water from their gills due to osmosis and also in their urine. Fish have to drink a lot of water to make up for the loss, however, as the water contains a lot of salt (35?) they must remove the excess salt from their system. The sodium and chloride ions are secreted by the gills and magnesium and sulphates are excreted in urine. This is an active process and requires energy much like the energy required to keep warm blooded animals warm.
When fish are under stress, one of the processes that is affected is ion regulation. This means they have difficulty adjusting the concentration of ions (sodium, chloride, etc.). Lowering the salinity of the tank water makes the concentration of ions closer to that of the fish"s internal fluids and reduces the fish"s efforts to maintain the correct concentrations.
Please note that only the higher bony fishes have lower osmotic concentrations and can be treated this way. Marine invertebrates have the same osmotic concentration as the surrounding water (Schmidt-Nielsen, 1975) and if left in the aquarium during hyposalinity treatment are most likely to die due to osmotic shock. Sharks and rays may not survive hyposalinity due to their unique method of osmoregulation. They have similar concentrations of salts to that of marine teleosts (one quarter to one third that of sea water), however, they also have very high concentrations of organic compounds which gives their internal fluids the same osmotic concentration as sea water. While some can adjust to lower salinities, most will succumb to osmotic shock just like invertebrates.


Cryptocaryon irritans (Ciliophora): primary infection in thick-lipped mullet, Chelon labrosus (Risso)


Development of specific PCR assays for the detection of Cryptocaryon irritans

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2413092
Taxonomic re-assignment of Cryptocaryon irritans, a marine fish parasite


Cryptocaryon irritans, a ciliated protozoan, is one of the most devastating parasites of marine fish cultured in temperate and tropical seas. Based on the remarkable affinities with its ?freshwater counterpart? Ichthyophthirius multifiliis, C. irritans has traditionally been included in the Ichthyophthiriidae, although cytological studies failed to show ultrastructural features to warrant its inclusion in this family. We sequenced the complete 18S rRNA gene (1,765 nucleotides) from aC. irritansisolate from the Red Sea. Our phylogenetic analyses unequivocally show that C. irritans is taxonomically distinct from I. multifiliis (15.4% divergence) and justify C. irritans' inclusion into the order Prorodontida within the Class Prostomatea. Cryptocaryonidae is proposed as a new family name.


Cryptocarion


Burgess, P.J. and Matthews, R.A. (1994). A standardized method for the in vivo maintenance of Cryptocaryon irritans (Ciliophora) using the grey mullet ( Chelon labrosus) as an experimental host. Journal of Parasitology, 80, 288-292.


http://www.jstor.org/pss/3283760
Immune response of fishes to ciliates



Ichthyophthirius multifiliis and Cryptocaryon irritans (Phylum Ciliophora)


Cryptocaryon irritans(Ciliophora): acquired protective immunity in the thick-lipped mullet,Chelon labrosus

http://www.sciencedirect.com/scienc...serid=10&md5=df28585ec269d040f7d158b83380d31b
Acquired protection toCryptocaryon irritanshas been demonstrated for the first time, using the grey mullet,Chelon labrosus, as an experimental host. Fish, immunized by controlled infections, established immunity against challenge infections withC. irritans, the degree of protection correlating with both intensity and exposure levels, with relatively few fish developing full protection. Protection lasted for six months in the absence of re-exposure to the parasite.



Cheers
Pedro Nuno;-)
 

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