Marine Ich


Commonly referred to as whitespot or marine-ich, Cryptocaryon irritans is one of the most common diseases to plague salt-water aquarium fish. It’s relatively unheard of in the wild

and is usually linked to several factors associated to an aquarium environment. Overcrowding, changes in water temperature, low pH levels, low dissolved oxygen levels and over exposure to ammonia nitrate or nitrite have all been known to trigger the disease.

Marine-ich is highly contagious and most salt-water aquarium fish are susceptible to this disease, with surgeonfish, cowfish, boxfish and pufferfish  particularly prone to suffer from the condition. However, eels and cartilaginous fishes such as sharks and rays demonstrate a degree of resistance to marine-ich.

Symptoms of marine-ich include fish rubbing themselves on aquarium decorations, loss of appetite, abnormal swimming behaviour, cloudy eyes, frayed fins, increased mucus layer, breathing difficulties and of course the small white spots which appear on the fish’s body. These are often described as looking like grains of salt or sugar and are responsible for the condition being known as whitespot.

Marine-ich is caused by an infestation of a protozoan parasite, Cryptocaryon irritans, which attaches itself beneath the skin of the fish, causing the characteristic white spots, where they feed on body tissue. During this stage the parasite is known as a trophont and it will normally feed on the fish for between 3 – 7 days. It then leaves its host, becoming what is known  as a protomont, and travels to the bottom of the aquarium.

When it reaches the bottom of the aquarium it turns into a capsule know as a tomont. It will remain here for between 3 – 28 days, during which time it produces hundreds of offspring know as tomites. The capsule then bursts releasing the tomites, who immediately start searching for a host fish to begin the process all over again.

If they can’t find a host fish they usually die within 24 hours. It’s during this free-living stage, when the parasite is a protomont, tomont or tomite, that it can be killed. Once it attaches itself to the fish and becomes a trophont the fish’s mucus layer will protect it from any available treatment.

There are a number of treatments available for treating marine-ich, with those containing copper or formalin or a combination of both being the most effective.  However, caution should be exercised when using these remedies. Copper is highly toxic to most marine creatures and will kill or cause serious harm to fish, invertebrates and living reefs.

The most effective and safest way to treat fish suffering from marine-ich is to place them in a quarantine – fish-only – tank during treatment. Fish should be quarantined for at least one month before being returned to the display tank. During this time any parasites in your display aquarium will have died because they won’t have had a host fish to feed on.

Another highly effective method to treat marine-ich is to gradually reduce the salinity of the aquarium water. To do this you need to reduce the salinity of your aquarium water by 2 ppt (parts per thousand), per day until the salinity is around 18 ppt.  This reduced salinity will kill-off any free-living parasites providing it is maintained for approximately one month. Again, it’s important to carry this out in a fish-only aquarium as living reefs, cartilaginous fish and invertebrates will not adapt to reduced salinity.

It’s also worth noting that increasing the temperature of your aquarium will speed up the life cycle of the parasite, aiding it’s growth to the free-living stage when it can be killed. However, this increase in temperature will result in less oxygen so make sure your tank is well aerated. Never increase the temperature beyond 82 Fahrenheit ( 28 Celsius).

Finally, although marine-ich is common and can be cured successfully, as with most salt water diseases prevention is better than cure. So it’s wise to quarantine newly purchased fish for at least a month before placing them in your display aquarium. This will give you an opportunity to monitor fish for the disease and to treat them if they are infected.

This post was written by

jasonjason – who has written posts on Home Tips Plus.
I'm a father of three, married and a home owner since 2006. I've worked in fixing up homes and rental properties.

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