Cryptocaryon irritans

Understanding and Treating Cryptocaryon irritans a.k.a. Ich

Greg Hix & Renee Coles-Hix

Whether you call it Ick, Ich, Cryp or Crypto, Cryptocaryon irritans is well known by every aquarist. Despite the fact it is discussed every day on forums, and could possibly be one of the first words you heard when entering the hobby, there still exist quite a few inaccuracies in terms of dealing with this parasite. Despite everyone’s awareness of its existence, many fish are still lost to this ailment. Why is there still so much confusion with such a common ailment?

Better decisions can be made about treatment options through better understanding. Therefore, the key to properly avoiding and/or treating fish infested with Ich is to fully understand its lifecycle. It can mean the difference of a failed versus successful elimination of the parasite from your fish and your tank.


What is Ich?

Ich is a ciliated protozoan parasite found on the body and in the gills of fish. It is an obligate marine fish parasite, which means, without the host, their life cycle cannot continue, and they will quickly die. They burrow to safety under the skin of their host before the lights go on, remaining out of our reach of our best efforts of eradication under the skin of their host remaining out of reach of our best efforts of eradication (Diggles, 1997).

cryptocaryon-irritans-2-left cryptocaryon-irritans-2-right

Even if your fish manages to survive the infection, the resultant damage can be profound. The pictures below show gill filaments pre and post-infection. Notice the blood flow and rich color of the healthy gill filament. The filament to the right is the aftermath of a single parasite. There is no blood flow throughout the affected tissue, and just one small horizontal vein visibly bringing circulation to the area. The health of this fish will be compromised its entire life and it will require the best conditions to survive long-term.

cryptocaryon-irritans-3-left cryptocaryon-irritans-3-right
What’s in a name?

So, how did Cryptocaryon irritans come to be coined Ich? It probably has to do with the similarities between it and the freshwater variety Ichthyophthirius multifiliis. In 1961, it was actually named Ichthyphthirius marinus, however, the researcher involved in the nomenclature didn’t realize at the time that his was not a new finding and the name Cryptocaryon irritans was actually given to the parasite 10 years earlier. It has also, by some people, been placed in the family Ichthyophyophthiriidae (Yambot, 2003). But you cannot be weighed down by the “correctness” of a common name. It is after all just that, a common name. It doesn’t have to be a shortened version of the scientific name.

Ich lifecycle

There are 4 distinct stages of the life cycle of crypto, which can last a minimum of 6 days, with the average being 11-16 days, at a temperature of 70-75 degrees. Why then, do we have to QT for longer? Because 2 weeks is the typical range; not the absolute. If you add up the maximum time frames of each stage below, you will find it can last up to 38 days. THEN you add in the variable of temperature and you have an extended survival time. Some strains have been observed to release theronts 72 days after leaving the fish.

Trophont stage (3-7 days)
– This is usually the stage where the parasite enters your system; while they are attached and feeding on your fish. It’s possible for the parasite to enter during other stages, but the occurrence/risk is minimal. This is the stage we visibly recognize as large white grains of salt. They feed 3-7 days and become more visible as they grow and mature. During these 3-7 days, they feed and get larger. Then, one morning you wake up and all the spots are gone. They’re cured, right?!! Wrong. You know nothing is that easy or simple in this hobby of ours…
The parasites have abandoned ship and have moved on to the next stage in their lifecycle.

Protomont Stage
(30 mins to 24 hours)
– In this stage, the parasites have left the fish and are looking for a suitable surface to adhere to. They “travel” along the substrate and rockwork to find a suitable place to reproduce. Once they adhere, they enter the next stage.

Tomont Stage (3-28 days)
– Once the parasite adheres to a surface, it encapsulates and begins to reproduce within its “shell”. This stage can last for 3-28 days. The babies then hatch and it’s on to the next stage.

Theront Stage (12.5-48 hours)
– The newly hatched parasites are free swimming and looking for a host or they will die. Once they find a host, the cycle starts again.

What to do if your fish and tank has Ich

There are many different treatment recommendations out there, from chemical to environmental, from food additives to praying. After visiting 5 main online reef forums, we made a list of the more popular treatments practiced or recommended. But whether you choose to use pharmaceuticals right down the option line to garlic, your best choice is to remove the fish from the tank and allow it to lay fallow for at least 6 weeks, preferably 3 months, although compliance may be an issue with this extended treatment time. 6 weeks will be ample for the average parasite, but you could be “lucky” enough to get the one that lasts for 72 days. If you go the fallow route, ALL of the fish must be removed whether they are showing symptoms or not. The cause of death of the host, is due to asphyxiation, osmotic imbalance and secondary infections (Diggles, 1997).cryptocaryon-irritans-cloudy-eyes

Symptoms include, but are not limited to:

  • White spots
  • Flashing or rubbing on surfaces
  • Rapid gilling/breathing
  • Loss of appetitecryptocaryon-irritans-white-spot
  • Loss of color
  • Cloudy eyes (How, 2015)
  • For scorpionfishes and lionfishes, frequent shedding.


Common Treatments


Copper needs to be dosed in a bare bottom quarantine tank. The live rock and many of the substrates we use in our tanks are composed of calcium carbonate, which can absorb the medication, leading to subtherapeutic copper levels. We’re not going to give dosing instructions, as it is very important to dose according to the instructions on the side of the bottle. Even if you follow the directions exactly you need to purchase a test kit for copper to monitor the levels daily. Too little will render the treatment ineffective and too much can easily kill your fish(Kawano, 2012).


Copper, although very effective at combating Ich,  is also known to be an immunosuppressive that can increase the chances of a secondary infection (Lewbart, 1996). It’s said some fish are also sensitive to the treatment, such as tangs, lionfish, puffers and mandarins, yet this is outdated and inaccurate information. Lionfish were once believed to be a scaleless fish. This belief today still exists and is still repeated on the internet and in forums. There are trusted articles out there, that were the most accurate at the time they were written, yet these too are outdated. Lionfish do not belong in this group. You will hear some people say they coppered their lion and they died. We’re afraid that scaled or not, the fish was going to die, and it just happened to be a lionfish. We have coppered lions and know of others that have coppered lions. Both times with a positive outcome in regard to the lion’s health and the Ich.



This treatment option is both effective and safe when used correctly. The salinity needs to be reduced to 1.009 – 1.010 to be therapeutic. Four – six weeks of this treatment should rid your fish of Ich, but can be extended safely up to a couple of months to be sure.  The fish can be removed from the tank and be placed in the hypo tank- (pH and temp matched to the display tank) tank without acclimation. However, when you again raise the salinity back to normal, it must be done slowly, with an increase of no more than 0.002 points per day. Research has supported that this may indeed make the treatment more effective. If you slowly lower the salinity, the Ich may be able to adapt, however, if you change the salinity quickly, more parasites will undergo cytosis. (Yambot, 2003). Once the treatment is complete, we just replace the evaporative water with salt water instead of fresh. It is important to use at least a refractometer when lowering your salinity to this level. Swinging arms and floating hydrometers are not consistently accurate enough to perform this operation.


There have been rumblings of a form of Ich resistant to hyposaline treatment. We too have experienced a strain that does not disappear after the normal amount of time. After three months in hypo, a fish was reinfected with Ich when returned to the main display. This tank was fallow for the duration of their treatment. At the time, we thought it was a strain with an extended encapsulation time and that the fish was indeed clean when re-entering the tank and was reinfected when the daughter cells were finally released. There have been documentation of this occurring under a controlled setting. Since that time, more research has been done and the existence of strains has been accepted as fact. These strains have differing ideas of what their ideal environment is. There is indeed a low salinity variant. There was an outbreak of crypto in waters with a specific gravity of 1.004 in Chiayi, Taiwan. This is lower than our fish could survive, thus hypo would be ineffective for this strain. How do we know we have that strain? We don’t. There was also another variant that adapted to the specific gravity of 1.004, but instead of continuing its life cycle, it went dormant in the encapsulating stage. When the salinity was raised, the parasite continued its life cycle, like nothing ever happened (Yambot, 2003).

Freshwater Dips

Dips are effective against many types of parasites. As a preventative treatment after purchasing the fish and before introducing him to the QT tank. They are, however, ineffective at eradicating Ich. For the dip to be effective, the Ich must be in the free swimming stage since they can be in the encystment stage for 28 days in some instances. The fish cannot tolerate the dip (and actually it’s a bath at that length, not a dip) for long enough to be effective. It may keep an episode of infestation down, as it kills some of the parasites that are burrowing or erupting from the skin and not at such a deep level as to be protected by the fishes slime and skin layers.

Formalin or Formalin + Malachite Green

Some people are under the impression that Malachite Green either contains or is related to copper. It’s true that the mineral malachite contains copper, but the name Malachite Green comes from the product being green, like the mineral. That’s the end of the connection between these two. Two studies have shown this treatment combination to be effective. In one such study, they used Formalin at 75mg/L and Malachite Green at 0.24mg/L. The duration of the treatment was 2.2 hours with 91.7% survival of the 24 fish treated (Pironet, 2000). The next study used 3.5g of malachite green per litre and 1:6000 of formalin. It does not state the length of the treatment, but that it was effective in eradicating the Ich infestation (Devesa, 1989).

Kordon has a product called Rid-Ich Plus. This product is actually a mixture of formalin and Malachite Green. We have not tried this product, but if we should need to treat in the future, this will be a product we’ll try.



This group of products are an anti-protozoan that claims to be reef-safe.  Some say it works, some say it doesn’t, and yet others say 50/50 chance. If you want to give it a try do so in a QT tank.

Pepper Based Medications

This group is again touted as a reef safe alternative. They help fish repel the parasite by irritating the skin surface so that they produce more mucous.  In the early stage, this may help keep numbers down, but will not remove it from your system. It WILL rear its ugly head again if this is the only intervention you implement.

Secret Solutions

Then there are the products that say they cure Ich, are reef safe, and won’t list their ingredients. Don’t use these products; don’t put anything unknown in your tank, especially if these products do not have independent studies to confirm their claims.

Picky Critters

Some suggest keeping cleaner shrimp and wrasses as a method of keeping Ich out of your system. While it is true these critters will pick at parasites, there is no way they can eradicate them from your system. Many of the protozoans are deep within the layers of skin on the fish…. deeper than any cleaner or wrasse will be able to go(Ros, 2010). There just are not very many natural predators of Ich out there because these huge infestations do not exist in the wild.


We see this suggestion very repetitively in the battle against Ich. Garlic, Allium satvum, has a reputation for being the “all-healing” herb. It does little to combat Ich itself, but it can help with immunity, so the fish can better fight off the infection. It also has been shown in studies to increase food consumption, which may be helpful in light of Ich’s anorexic effects (Lee, 2012)(Talpur, 2012). This should not be the only intervention and should be considered as effective as vitamin “C” against the cold. It’ll help boost your immune system, but if you have a cold, you have a cold (Sasmal, 2005). Some swear garlic was the sole reason the Ich disappeared in their tanks. There is zero data to reflect that. More than likely it was due to the natural lifecycle of the parasite or due to the next topic, immunity.


Fish can actually develop immunity after a survived exposure to Ich. They can have a total immunity or partial, which helps them ward off large infestations, while low level infestations are allowed to exist (Bai, 2008). In these mild infestations, the typical white spotting may go unnoticed, as there is only a scattered and intermediate appearance. Then, when something occurs in your tank to stress your fish, their immunity drops and more parasites attach to feed. The numbers get out of control and it becomes apparent that you have a problem. Vaccines have been developed, yet are not available to the hobbyist. Its usefulness in aquaculture is limited as it is impossible to vaccinate every fish in a fish farm. Vaccines that are administered via other modes are being developed, yet nothing has been as effective or practical such as individual injections (Yambot, 2006).

Quinine Sulfate

This medication has claimed to eradicate resistant strains of Ich, where hyposaline treatment has failed. Effective? One study showed there were significantly reduced numbers of C. irritans trophonts, but only for part of the therapeutic duration. Up to day 3, the treatment seemed to be effective. Then, by day 5, there were insignificant differences between the two groups. The two groups in this study being those who were and those who were not, medicated with quinine (Rigos, 2013). We used it in a display tank setting in order to evaluate whether or not the system’s biofiltration would be compromised, and the Ich was gone for some time after that, but that tank went through a cycle and the fish subsequently died.


People speak of the quarantine (QT) process like it was the cure for Ich.

  • “If you QT all new fish, you won’t have to go through it (Ich) again.”
  • “After that incident (with Ich), I QT everything I buy and I mean everything.”
  • “Clown with ICH! I QT’d all my fish.”

Will a proper QT ensure an Ich-free tank? Nope. Without prophylactic treatment, there is a chance that Ich will enter your display unbeknownst to you. We’re not saying an untreated QT doesn’t have value, but it in no way is it an assurance that your fish doesn’t have Ich. An adequate QT is the best chance we have at spotting the parasite before it enters, as a newly acquired fish in QT has a high level of stress. This is the opportune time for Ich to grab a foothold. If you want to be sure, treat every fish entering the tank and QT every non-fish item that is to enter thereafter. Is it worth the trouble? Some people swear Ich will not find its way into their display, even without treatment and with just a watchful eye and a lengthy quarantine. Did you know there was a strain of Ich that infests only the gills? They do not infest the body. They do not infest the eyes. They only gather out of sight, behind a fish’s operculum.

Just sayin…. 🙂


NO, Ich does NOT have a shelf life

The word around town is that Ich will “burn” itself out in under a year if left alone to live communally with the fish. One word that keeps popping up again and again, is inbreeding. Inbreeding is defined as “to breed individuals of a closely related group repeatedly.” This is not the way Ich reproduces. Ich parasites do not breed with other Ich parasites. All they need is a comfy place to create a cyst in which to clone a bunch of little daughter cells. In one study, the researchers were unable to keep the parasite alive for anything over 10-11 months or 34 cycles and it was attributed to senescence (Dan, 2009). Rather than dubbing the organism self-limiting based on one study, additional data should have been considered, as when the test was repeated, the parasite was kept alive for over two years. In another study, they had used a sample collected in 1994 from a culture started and maintained since 1989. That’s five years! Our own experiences match this data as we had Ich show up in our 100g tank in December of 2011, and make a reappearance some 1 year and 7 months later. Nothing was added to this tank. Trust us, when starting a business and then throwing in back surgery, they were lucky they got fed. If you hear the “self-limiting” argument in a discussion, simply list the following reference and quote and tell them science says they are wrong.

DIGGLES, B., & ADLARD, R. (1997). Intraspecific Variation in Cryptocaryon irritans. The Journal of Eukaryotic Microbiology, 44(1)4.

The isolate obtained from the USA was a DNA sample extracted from C. irritans theronts collected in September 1994 from a culture maintained since 1989 at the University of Georgia by serial passage on black mollies (Poecilia hybrid).

That myth has been BUSTED!

Why everyone has a different bedtime story

Nothing can evoke anger on a forum quite like an Ich thread. Why is everyone is so angry? We all share to the best of our ability, the experiences we have had. How can stories that are so vastly different, all be correct? This question means someone is seen as inherently wrong, and hence tempers flare. But are they wrong? We may all have success doing opposite interventions due to variables in any given situation. Variables like tank environment, fish species/origin and different strains. So how do we ever choose an effective treatment plan? Choose from the treatments listed which have been the MOST successful. We’ve intervened and have had fish live and have had fish die. We’ve done nothing and have fish live and have had fish die. We’ve even used products like Kick Ich years ago and still had some fish live and some die. If our own successes can vary so much, how can we expect one pathway to work for everyone? If we can remember all of us can be right at the same time, maybe there would be more productive Ich threads than closed ones.


Suggested Further Reading, Websites and References:
Bai, J. S., & Xie, M. M., Zhu, X. Q., Xue, M. D., & Li, A. X. (2008). Comparitive studies on the immunogenicity of theronts, tomonts and trophonts of Crytocaryon irritans in Grouper, Parasitology Research, 102 (307 – 313).

Beck, K., Lewbart, G., & Piner, G. (1996). The occurrence of an Ichthyobodo ‐like organism on captive Atlantic spadefish, Chaetodipterus faber (Broussonet). Journal of Fish Diseases, 19 (111- 112).

Bo-Young Jee, Ki Hong Kim, Soo-Il Park, & Yi-Cheung Kim. (2000). A new strain of Cryptocaryon irritans from the cultured olive flounder Paralichthys olivaceus, Diseases of Aquatic Organisms, 43 (211-215).

Bryant, M. S., Lee, R. P., Lester, R. J. G., & Whittington, R. J. (1999). Anti-immunoglobulin antisera used in an ELISA to detect antibodies in barramundi Lates calcarifer to Cryptocaryon irritans, Diseases of Aquatic Organisms, 36 (21-28).

Burgess P. J. (1992). Cryptocaryon irritans Brown 1951 Transmission and immune response of mullet Chelon labrosus (Risso, 1826). PhD thesis, University of Plymouth.

Burgess P. J., & Matthews, R. A. (2005). Fish Host range of seven isolates of Cryptocaryon irritans,Journal of Fish Biology, 46 (727-729)

Colorni, A., (1985). Aspects of the biology of Cryptocaryon irritans, and hyposalinity as a control measure in cultured gilt-head sea bream Sparus aurata, Diseases of Aquatic Organisms, 1 (19-22).

Colorni, A., & Burgess, P. (1997). Cryptocaryon irritans Brown 1951, the cause of “white spot disease” in marine fish: An Update, Aquarium Sciences and Conservation, 1 (217-238).

Devesa, S., Barja, J., & Toranzo, A. (1989). Ulcerative skin and fin lesions in reared turbot, Scophthalmus maximus (L.), Journal of Fish Diseases, 12 (323 – 333).

Dan, X. M., Li, A. X., Lin, X. T., Teng, N., & Zhu, X. Q. (2006). A standardized method to propagate Cryptocaryon irritans on a susceptible host pompano Trachinotus ovatus, Aquaculture, 258 (127 – 133).

Dan, X. M., Lin, X. T., Yan, Y. X., Teng, N., Tan, Z. L., & Li, A. X. (2009). A tenchnique for the preservation of Cryptocaryon irritans at low temperatures, Aquaculture, 297 (112-115).

Diggles B. K., & Adlard, R. D. (1997). Intraspecific Variation in Cryptocaryon, Journal Eukaryotic Microbiology, 44 (25-32).

Diggles, B. K., & Lester, R. J. G. (1996). Infections of Cryptocaryon irritans on wild fish from southeast Queensland, Australia, Diseases of Aquatic Organisms, 25 (159-167).

Fish Diseases and disorders, Vol. 1. Protozoan and Metazoan Infections, 2nd ed, CABI, Oxford, pp. 391-416.

How, K. H. Zenke, K., & Yoshinaga, T. (2015). Dynamics and distribution properties of theronts of the parasitic ciliate Cryptocaryon irritans, 438 (170 – 175)

Kawano, F., & Hirazawa, N. (2012). Antiparasitic effect of in-feed inhibitors of folic acid synthesis and dihydrofolate reductase against coliate Cryptocaryon irritans infection in the red sea bream Pagrus major and against ciliate Ichthyophthirius multifilis infection in black pop-eyed goldfish Carassius auratus, Aquaculture, 330 (1-7).

Lee, J. Y., & Gao, Y. (2012). Review of the Application of Garlic, Allium sativum, in Aquaculture,Journal of the World Aquaculture Society, 43 (447 – 458).

Pironet, F., & Jones, B., (2000). Treatments for ectoparasites and diseases in captive Western Australian dhufish. Aquaculture International, 8(4), 349-361.

Rigos, G., Karagouni, E., Kyriazis, I., Athanasiou, E., Grigorakis, K., Kotou, Efthimia, K., & Katharios, P. (2013). In vitro and in vivo evaluation of quinine in gilthead sea bream, Sparus aurata naturally infected with the ciliate Cryptocaryon irritans, Aquaculture, 416 (185 – 191).

Ros, A. F., Lusa, J., Meyer, M., Marta, S., Oliveira, R., Brossard, M., & Bshary, R, (2010). Does access to the bluestreak cleaner wrasse Labroides dimidiatus affect indicators of stress and health in resident reef fishes in the Red Sea, Hormones and Behavior, 59 (151 – 158).

Sasmal, D., Babu, S., & Abraham, J. (2005) Effect of garlic (Allium sativum) extract on the growth and disease resistance of Carassius auratus (Linnaeus, 1758), Indian Journal Fish, 52 (207 – 214).

Talpur, A. D., & Ikhwanuddin, M. (2012) Dietary effects of garlic (Allium sativum) on haemato-immunological parameters, survival, growth, and disease resistance against Vibrio harveyi infection in Asian sea bass, Lates calcarifer, Aquaculture, 364 (6 – 12).

Xiao-Chun, L., Ming-Quan, X., Xing-Quan, Z., & An-Xing, L. (2007). Protective immunity in grouper (Epinephelus coioides) following exposure to or injection with Cryptocaryon irritans, Fish & Shellfish Immunology, 22 (427 – 432).

Yambot, A. V., & Song, Y. L., (2006). Immunization of grouper, Epinephelus coioides, confers protection against a protozoan parasite, Cryptocaryon irritans, Aquaculture, 102 (307 – 313).

Yambot, A. V., Song, Y. L., & Sung, H. H. (2003). Characterization of Cryptocaryon irritans, a parasite isolated from marine fishes in Taiwan, Diseases of Aquatic Organisms, 54 (147-156).

Yoshinaga, T., & Dickerson, H. W. (1994). Laboratory Propagation of Cryptocaryon irritans on a Saltwater-Adapted Poecilia Hybrid, the Black Molly, Journal of Aquatic Animal Health, 6,3 (197-201).