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  • Marine Ich - Myths and Facts

    I found this while looking into John's question yesterday. Credit given at the end of the article.

    Marine Ich (Cryptocaryon irritans)

    One of the marine aquarist’s devils. So many articles have been written about it. Many are long or are in multiple parts. A lot is known about this marine fish disease because of the many $$$ put into research by the fish farming and aquaculture industries. First discovered (or the better word is 'noticed') in the 1800's and later more understood in the 1900's, we’ve learned about all there is to know about this parasite by the 2000's.

    I don’t want to write a long post on Marine Ich (MI) but the reader, in as brief of space as possible, should know some truths. The aquarist 'sees something' and then 'guesses' as to what it means and thus starts another round of rumors. It's almost a type of voodoo. It's easier to listen to a rumor of a short absolute statement then it is to read and understand the results of decades of studies and experiments. It is easier to try and take shortcuts with this disease by believing the parasite to be able or capable to do things or die from things it just can't, then it is to do the work to kill it, control it, or prevent it by the means that are known to work.

    If you think your fish might be infected, this is the post you should read and follow: Curing Fish of Marine Ich

    It's time to separate out the rumors from the facts and the subjective observations (which start rumors) from actual scientific studies. In bullet form, here’s what is known:

    Life and Visuals:

    1, The parasite has several ‘stages’ in its life cycle. Cyst in aquarium (usually on substrate, decoration, wall, equipment, or rock) ruptures into free-swimming parasites that burrow into fish, grow into a visible white nodule that is ‘pregnant’ with more parasites, that usually falls off the fish to form a cyst that starts the cycle over again.

    2. Only time a human can see this parasite with the naked eye is when it is ‘pregnant’ on the fish and has formed a white nodule. (The white spot is about the size of a grain of table salt or sugar).

    3. Parasites that have just burrowed into the fish are not visible until 2.

    4. Cycle can be completed in less than 7 days, but usually within 24 days BUT can go as long as 72 days. Literature usually quotes ‘average’ number of days. 72 days is rare; 60 days usually encompasses more than 99.9% of the observations and research.

    5. This is not the same as the freshwater disease, Ich (Ichthyophthirius multifilis) but it was named after it?! This leads freshwater aquarists to thinking the wrong things about Marine Ich, adding to the myths and rumors.

    6. MI is not very sensitive to temperature changes. That is, increasing the temperature does not significantly decrease the life cycle time. This is not true with Freshwater Ich (which is where this rumor of raising the temperature on a marine aquarium with MI comes from).

    7. MI can live and reproduce in temperatures as low as 50F and as high as 90F. Thus temperatures that would kill MI would first kill or severely stress most tropical marine fishes.

    8. Spots appear then disappear as MI goes through its cycle. Remember 2. This 'disappearing act' is what leads uninformed aquarists to believe the fish are cured. This is the dumbest thing aquarists can possibly think about this parasite!

    9. Parasite likes infecting the fish’s gills. The tissue there has more water passing by so there is an increase in chance the free-swimming parasite will get to the gill. This is one reason why fast breathing (over 80-90 swallows in one minute) is one of the symptoms of possible infection.

    10. The parasite burrows into the fish, below the mucous layer and into the skin. (This is why cleaner fish/shrimp can’t get to it in order to remove them from the fish). The second dumbest thing an aquarist can think: I'll get some cleaner fish or cleaner shrimp to remove/eat the parasite. THESE MARINE LIFE DO NOT EAT THE PARASITE NOR WILL FISH OR SHRIMP REMOVE THE PARASITE FROM THE INFECTED FISHES.

    11. Parasite is transmitted in water (free-swimming and cyst stages), or by falling off of an infected fish (even one that seems healthy because of 9.). This means that water OR fish from another aquarium can carry the disease to another aquarium.

    12. The parasite can infect bony fishes, including eels, sharks, and rays, though many species of fish, like Mandarins, have a good resistance to MI, they can still be infected and can harbor or carry the parasite. Invertebrates, snails, crabs, corals, plants, etc. are not affected/infected by MI, but the MI can be in their water, shells, etc.

    13. There is no such thing as a dormant stage for MI. The parasite can’t wait around for another host. It MUST go through its cycle. Dr. Burgess recorded that in the cyst stage, he found the longest existing cyst to last for 60 days before releasing the free-swimming parasites. This is rare but possible.

    14. INTERESTING FIND: If no new MI is introduce into an infected aquarium, the MI already there continues to cycle through multiple generations until about 10 to 11 months when the MI has ‘worn itself out’ and becomes less infective. A tank can be free of an MI infestation if it is never exposed to new MI parasites for over 11 months.


    1. Hyposalinity - Using a refractometer, hold salinity at 11ppt to 12ppt until 4 weeks after the last spot was seen. (Best to use salinity, but if you use specific gravity, that equates to roughly 1.008 to 1.009 sp. gr. units). Raise salinity slowly and observe fish for 4 more weeks. Hard to control pH and water quality during treatment. This is the least stressful treatment for the fish. See: http://www.reefsanctuary.com/forums/...t-process.html

    2. Copper treatment - Follow medication recommendations. Can be effective in 2 to 4 weeks of treatment. After treatment, remove all copper and observe fish for 4 more weeks. Copper is a poison to the fish and creates some stress. The fish may stop eating. See end of this post for other things that can go wrong. See: http://www.reefsanctuary.com/forums/...-problems.html

    3.. Transfer method - Fish is moved from tank to tank to separate the fish from the cysts that fall off and the free-swimming stages of the parasite. Two hospital tanks are needed to perform this treatment. The fish is stressed by having to keep moving it between these hospital tanks.

    4. Only the above 3 known readily available cures work almost 100% of the time. Other chemicals will kill the MI parasite, but only in special conditions (not good for the fish) or in lab experiments (not using marine fish). Some chemicals will only kill some of the organisms, letting the others escape death to go on to multiply and infect. There are certain (human) prescription drugs that will work also, but they are not available to the public and really shouldn't be used when these three are so effective. (Those drugs still require a quarantine tank treatment).

    5. Not any of the treatments can be done in a display tank with true live rock. Must be done in a hospital tank or quarantine tank. The hyposalinity and the copper treatment would kill invertebrates, live rock, and other non-fish marine life. Substrates and carbonates interfere with a copper treatment. Use artificial SAFE decorations in the QT.

    6. No known ‘reef-safe’ remedies work consistently. Many aquarists think a particular remedy works when in fact the fish acquire an immunity or defense against the parasite. It’s easy for any manufacturer to have an independent study done on the effectiveness of the ‘reef-safe’ remedy but they don’t because. . .

    7. Cleaner shrimp and cleaner wrasses are not known to pick these parasites off of fish. (See 10. above).

    8. Freshwater dips can kill some of the parasites on/in the fish, but not all of them because many of the parasites are protected by the fish's skin and mucous layer. (See 10. above).

    9. No dip can get rid of these parasites because primarily of 10. above.

    10. Let aquarium go fishless (without any foreign saltwater additions (e.g., water from LFS system, water from another tank or system -- use only distilled or RO/DI for evaporation and freshly made, uncontaminated salt water for water changes), without contamination from infected tanks, live rock additions, etc.) for at least 8 weeks and the tank will be free of MI. This 'fallow period' has over a 99.9% chance of success. Keep the aquarium running normally -- lighting on as usual, pumps, filtration, feeding inverts, and maintain normal tropical temperatures (78F is good).

    11. NEVER combine a copper treatment with a hyposalinity treatment. In hyposaline solutions it is hard to control pH. When pH fluctuates (down) the copper present can be lethal to marine fishes. When using certain complexed copper medications, like Cupramine, the two can be used together with greater safety. However I strongly advise even doing this. During a hyposalinity treatment, it is hard to control the pH. The buffering ability of the water is very weak, so pH shifts are very easy. In the presence of a copper medication, a sudden drop in pH can cause copper poisoning to the fish. BOTH the copper and hyposalinity treatment poses some stress to the fish. Should they have to endur both? Just choose one and do it properly. Follow the process to make the determination on the way you want to treat the infected fish, found here: Curing Fish of Marine Ich

    Defense and Immunity:

    1. The fish’s mucous coating can provide some protection from the parasite. The mucous coating is where some fish immunity develops.

    2. When water temperature drops, mucous coating is often reduced or lost in marine fishes, that is why sometimes MI becomes visible on the body of the fish after a sudden drop in temperature. This meant, however, that the disease was present and living in the aquarium, infecting fish without the aquarist having been aware of it.

    3. No fish, no matter how good its defense is, can stop being infected. A healthy fish will and can be equally infected as a sick or stressed fish. What happens is the aquarists sees one or more fish with the disease and assumes because none are seen on the other fish in the aquarium that they are 'disease free.' NOT. Aquarists can't always see the parasites. See above top, 2., 3., and 9. All fish in an infected tank require treatment.

    4. A weak, stressed, or sick fish will die sooner than a healthy fish, but is no more likely to get infected than the healthy fish.

    5. A fish that survives an attack may develop proteins in the mucous coating that will help fend off the parasite (this is a type of immune response). An immune fish will usually not show being infected. Unfortunately. . .(see 6. below). . .

    6. An immune fish doesn’t remain immune. Separated from the disease for months, the once immune fish can become MI infected. OR if the immunity weakens, the fish will be attacked.

    7. Immunization seems to work, but not affordable or likely available to the hobby for many more decades. The immunization materials are hard to make, expensive, and slow to produce. Immunization usually only works for several months at a stretch.

    Subjective and Non-Subjective Observations, Claims, and Common Myths

    1. Some Tangs seem more susceptible. True. Their mucous coatings are reduced in thickness and composition. They swim up to 25 miles a day in the ocean in search for food so maybe Mother Nature provided them with this as a means of 'escape.'

    2. It goes away on its own. Untrue. Only visible at one stage IF it is on the body or fin of the fish. It’s the life cycle. If it was once seen, then it hasn't gone away -- it's just not visible to the aquarist.

    3. It goes away with a ‘reef-safe’ remedy. Untrue. This is one of the biggest and most 'dangerous' of the misrepresentations in the hobby. The aquarist thinks everything is okay when it isn't. What usually has happened is that the parasite has killed the fish it will kill and the rest have developed a resistance or immunity. The parasite is still in the aquarium, possibly infecting the gills of the fish where it can’t be seen.

    4. It was gone then when a new fish is added, it is there again. Not true. See 3. It wasn’t gone or the new fish brought in the disease with it. A new addition to an aquarium can be the stress which triggers the other fish to reduce their defense or immunity, thus allow the parasite to 'bloom' to the point where the infection is now visible to the aquarist.

    5. The fish lived the last outbreak then died during the second or subsequent outbreak. Can be true. The fish had a resistance or immunity that it lost.

    6. It was accurately diagnosed as MI spots, then never showed up again. It wasn’t MI or the fish quickly developed an immediate immunity or resistance, or the fish is still infected in the gills.

    7. MI can ‘hang around’ almost unnoticed with just a body spot now and then because it often resides just in the gills. True. So ‘it is gone’ after ‘it was here’ is very unlikely.

    8. Aquariums always have MI. Untrue. MI can be kept out of an aquarium. Just quarantine all fish and don’t let non-quarantined livestock get into the aquarium. After keeping thousands of marine fishes, my home aquariums have been free of MI since 1970.

    9. Fish always have MI. Untrue. In the wild they often show up to 30% infected (or more) but the wild fish survive minor infections. In the tank the parasite can 'bloom.' In the tank the fish can't get away. The combination of bloom and no escape will overcome the fish. In capture and transportation the fish can share the disease and thus many wild caught marine aquarium fishes do have this parasite, but not all.

    10. Like 9. a fish can't be made to be totally rid of MI. Untrue. All marine fish can be cured and rid of any MI infection.

    11. Just feed the fish well and/or feed it garlic and it will be okay. Untrue. I compare this approach to this one: "Granny has pneumonia. Let's keep her home rather than take her to the hospital. We'll feed her well with chicken soup and vitamins." Nutrition, foods, vitamins, etc. don't cure an infected fish. An infected fish is sick and is being tortured by the itching and discomfort. It might pull through and obtain Resistance or immunity (see above) but while you sit comfortably in your home, the fish is being stressed by having to contend with a parasite. Don't let this happen to the fish. Cure it!!

    12. A new cure has been discovered. Unlikely. If the aquarist thinks they have found a new cure, then have it researched and independently tested. It's easy and cheap. If it is as good as the above 3 then the professional veterinarians, private and public aquariums, fish farms, and I will use it. The aquarist needs to keep the perspective of how devastating this parasite is not to just the hobby but to the whole fish farming industry. Any new way of 100% treatment will make headlines!

    13. If the MI can't always be detected, then why bother with a quarantine procedure? In the confines of a small quarantine and being there for no less than 6 weeks, the MI parasite will make itself known because the fish is weakened and the fish can't get away from being re-infected by multiplying MI parasites. In other words, the quarantine procedure instigates a 'bloom' of the parasite which will make it visible to the aquarist.

    14. All white nodules fall off the fish and move on to the cyst stage. Untrue. It has been discovered that, on very rare occasions (why we don't know) the white nodule will encyst and rupture while still on the fish.

    15. UV and/or Ozone kills MI. Ozone doesn't kill all parasites that pass through the unit, nor does the water treated with ozone kill the parasites. UV only kills the parasites that pass through the unit. Not all MI parasites will pass through the unit, so the UV will not rid an aquarium of MI. A UV can help prevent a 'bloom' of the parasites however, and thus help in its control. UV is not a cure nor a preventative measure for MI.

    16. Spots are MI. Untrue. Probably one of the most problematic causes for rumors and myth-information in the hobby is assuming the spot is Marine Ich when it may be one of another few dozen other parasites or conditions (e.g., pimple-like reaction to infection) that look like Marine Ich. The mis-diagnosis is often the cause for claims of what cured MI, when the fish didn't have MI to start with.

    17. My LFS quarantines their fishes for 2 weeks and I only buy them to be sure they are healthy and free of MI. Have you been reading the above? The 2 weeks is not long enough. Was the 2 weeks in isolation or is the fish's water mixed with other fish's water? Seeing is not believing, right? LFS employees don't have time to closely observe and study the fishes they have in stock, for a full 6 weeks. The truth is out there. . .Trust no one.


    Leebca – reef sanctuary
    This article was originally published in forum thread: Marine Ich - Myths and Facts started by hooked View original post
    Comments 10 Comments
    1. bazeball05's Avatar
      bazeball05 -
      That link has 4 other links to go to! Haha linkception. Haha

      But on real note, thank you, I appreciate the reads
    1. FireDawg56's Avatar
      FireDawg56 -
      That is a great article! I have had it under my favorites as a rescue resource

    1. Levi's Avatar
      Levi -
      +1 great article
    1. Joe's Avatar
      Joe -
      This is a great resource.
    1. Sharkboy99999's Avatar
      Sharkboy99999 -
      Do you qt carols

      Sent from my iPhone using Tapatalk
    1. kmellon's Avatar
      kmellon -
      It is always a good idea to both dip and QT corals. I've seen several posts from others about the different dips that didn't quite take care of everything to include eggs so dipping and qt limit the possibility of getting some nasties in your tank. Also keep in mind that some dips flat out state that you need to keep corals in a qt with good carbon and no inverts to let their treatment clear off the frags. I think RPS All out is what I read that on.
    1. Levi's Avatar
      Levi -

      Sent from your LG G2 using Tapatalk
    1. static reef's Avatar
      static reef -
      Bump. Great read
    1. sliver's Avatar
      sliver -
      Great read. thanks for posting.
    1. Coral Highlights's Avatar
      Coral Highlights -
      Very informative, and answered a lot of questions I have asked other people in the past. Thank you for posting this.