Fish Quarantine: Treatment for Marine Ich

Cryptocaryon irritans (also known as marine Ich) is a parasite similar to freshwater ich in that both present as small white dots (look like sand or salt) that cover the fish’s body.  Both types cause fish to “scratch” themselves on rocks or shake their bodies in an effort to rid themselves of the parasite.  Saltwater fish may also try to utilize cleaner shrimp or cleaner wrasses if available to help eradicate the parasite.  The parasite typically comes into the aquarium on an infected fish, and less likely in the water or attached to live rocks, corals, etc. 

Purple Tang with Cryptocaryon Irritans (and HLLE)

Treatment Background

Fish of all types are susceptible to the parasite, some more than others.  Unless an aquarium has had all inhabitants treated for cryptocaryon irritans, then an infestation will likely happen at one point or another.  However, ich is not present in every aquarium.  There is a common misbelief that every aquarium has ich and will always have ich.  This makes “herbal” treatments and other folk treatments more common than proven methods of eradication.  Unfortunately, there are no in-tank treatments for marine ich either, which makes aquarists even less likely to treat marine ich correctly.  The way I like to think about ich is like fleas.  Fleas will only come into your house on something infected (animals and sometimes clothing).  The only way to treat for them is to kill the adults and the eggs.  Once they are gone, they are gone.  You may have a re-infestation, but that’s another separate incident.  The common misconception is that feeding certain foods (like garlic) will boost the fish’s immune system to the point where the “fleas” (i.e. marine ich) will not cause an issue.  The misconception also believes the “fleas” will always exist no matter what quarantining/treatment effort.  This simply does not make sense.  Eradicate the parasite and prevent further infestations. 

Quarantine and Treatment

Unfortunately, Cryptocaryon irritans can often present itself in the fish’s gills before spreading to the rest of the body.  By the time an infection is identified, the fish is usually too far gone to save.  Brookynella and Amyloodinium (marine velvet) can also start in the gills thus making correct diagnosis nearly impossible without a gill biopsy.  Additionally, a lack of white spots on a fish does not mean it is healthy.  The marine ich could be in the gills or in another part of its life cycle (they leave the fish to reproduce). This is why a quarantine and treatment system is so crucial. 

As I have stressed in previous blogs, I suggest always having a QT tank on hand, no matter how simple, with an airstone, hang-on-back filter or sponge filter, heater, thermometer, and some PVC for hiding places.  I also keep the following medications on hand:  Formalin (formaldehyde), Furan-2, Erithromycin, Chelated Copper, PraziPro, Methylene Blue, Selcon, and VitaChem.  Treatment of all fish before introduction to the main aquarium can save lots of time and money in the long run.

Due to the increased risk, I do not recommend quarantining multiple fish as in the photo below (three female Watanabe Angels).  These angels were in a hyposalinity treatment quarantine, which allowed the use of dry rock and PVC for hiding places.

Copper Treatments

Although copper-derivative treatments will ward off a variety of diseases (which is why so many local fish stores use it), I prefer to go the more “natural” route as copper has been shown to cause problems in the reproductive health of various fish, is difficult to test, and creates a fairly hostile environment for fish.  I use it only when I believe it is necessary for the health of the fish.  However, it does work as a treatment, and if you are comfortable in its use, then more power to you.

Tank-transfer Treatment and Life Cycle Issues

A second proven treatment is the tank-transfer treatment.  In order for this treatment method to work, a deep understanding of the parasite’s life cycle is required.  Tomites (like babies) are released from the tomonts (like adults) attached to live rock, aquarium glass, etc.  Once the tomites are released, they become known as theronts (like kids).  The theronts swim through the aquarium and wreck havoc.  If they do not find a fish host upon which to feed, they will die (approximately 16 hours).  Once the theront has settled down onto a fish host, it becomes a proront (like teenagers).  Once the proront encycsts on the fish and begins to feed, they become trophonts (like young adults).  After the trophonts mature, they leave the host and shed their cilia (protomont stage…like settled-down young adults).  The protomonts find a suitable hard surface (live rock, aquarium glass, etc) on which to attach and then become tomonts.  The tomonts reproduce the tomites, and the cycle continues.  Exact life cycle times depend on aquarium temperature, salinity, and even species.  Due to this complexity, I do not recommend this treatment for most aquarists, but the concept is that the fish will be removed and placed into a new aquarium with new water every couple days or so to prevent reinfection by the theronts.  Although this is a complex system, it is a very quick treatment method (days vs weeks.)

Hyposalinity Treatment (preferred)

I personally prefer hyposalinity (low salinity) treatment for all fish.  With a refractometer, it is quite simple to maintain.  The parasite cannot survive in most stages of its life in hyposalinity due to the osmotic imbalance.  This treatment takes approximately 6 weeks to complete, but it is very comforting and safe for almost all fish.  In order to perform hyposalinity treatment, the fish is placed into a treatment tank by itself, and over a few days, the salinity is lowered (assuming a start of 35 ppt) down to 14 ppt.  Since the internal salinity of a fish is 11-12 ppt, the fish has to work less for osmoregulation.  This allows the fish to recover from any shipping/stress injuries faster.  Antibiotics also work better at lower salinities.  A broad-spectrum antibiotic should be used as a secondary infection may occur as the trophonts leave open wounds on the fish.  After 6 weeks, the salinity is raised ~2ppt per day until back to ~35ppt. 

Male Japanese Swallowtail Angel in Hyposalinity Treatment


Avoid herbal, in-tank, and folk-tale remedies as these will only prolong the inevitable:  the death of a fish.  Proper treatment with a proven method (copper, tank-transfer, or hyposalinity) will eradicate the pest and prevent future infections.  Treatment in a separate aquarium minimizes the loss (one fish versus an entire aquarium full of fish infected with the parasite).  Which treatment selected should depend on the knowledge and comfort of the aquarist with that particular treatment.


2 pings

  1. Leopard Wrasses Demystified » Reef'd Up Aquatics

    […] treatment choice is hyposalinity.  Hyposalinity is very safe as the fish does not have to work as hard to maintain osmotic balance […]

  2. How to Freshwater Dip Fish » Reef'd Up Aquatics

    […] (marine velvet), Uronema, flukes, and other nasties (Noga, 2010).  No, it doesn’t work on marine ich (Cryptocaryon irritans), but still, it’s a great start to having healthy […]

Leave a Reply