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Ichthyophthirius (ICK)

(Cryptocaryon irritans)

(“white spot” disease)

(About.com - Saltwater Ich (Cryptocaryon))


Ich is a highly contagious parasitic infestation caused by the protozoan Ichthyophthirius Multifillis and its saltwater counterpart Cryptocaryon Irritans.

The parasite burrows itself under the fish’s skin in order to feed and grow, causing skin irritations and osmoregulatory disturbances that allow secondary bacteria and/or fungi to enter the skin. It is notable that Ich alone is not fatal. Fatalities occur mainly through secondary infections.

In advanced cases, the parasite will attach to the gills, causing an interference with the oxygen carrying cells, thus depleting oxygen.

Symptoms of Ich include the well know ‘salt grain like’ white spots (Ich is often referred to as “white spot” disease). As the infection spreads other common symptoms are rubbing against decorations, breathing difficulties, loss of appetite and increased mucus layer (washed off slime coat), cloudy eyes, frayed fins, and abnormal swimming behavior.

Ich has to be present in the aquarium to cause an infestation. Frequently cited temperature fluctuations are not responsible; neither are other stress causing conditions alone or in combination.

The Ich parasite can be introduced by new arrivals of fish, or be dormant in the aquarium itself. Healthy fish can live with a balanced host–parasite relationship for a long time. The healthier the fish the more difficult it becomes for the parasite to re-produce, which in turn keeps their population under control.

New arrivals with a weak and unprepared immune system are extremely susceptible for the parasite and are ideal victims for parasitic infection.

The unexpected appearance of Ich without new arrivals is usually caused by deteriorating water parameters which weaken the fish’s immune system.

Excess nutrients, nitrates, fluctuating pH, ammonia, low dissolved oxygen content and other stress causing factors will lower the fish’s’ immune system and may lead to an outbreak which could have been avoided by good aquarium maintenance. Nevertheless the parasite has to be present in order for the disease to break out.

The life cycle of Ich includes 3 stages. The mature parasite (trophozoites) forms pustules in the skin in order to feed (visible as white spots). Once the pustule ruptures, the trophont settles at the bottom of the tank. Secreting a coating it forms a protective capsule (cyst). Within, the parasite performs a series of cell divisions creating hundreds of new cells (tomites) which are released and search for a new host.

There are about 300 tomites leaving the cyst. Tomites have to find a host within 3 days or they will die off. The complete parasitic life cycle ranges from 14 to 16 days. Higher temperatures accelerate the cycle while lower temperatures will extend the parasitic activities.

The three day duration of the tomite stage is the only stage in which the parasite is vulnerable and can be treated with medication. This limited vulnerability explains why it is necessary to repeat the treatment to assure that all parasites have been eliminated. Not completing the treatment due to no reoccurring symptoms (white spots, etc.) usually leads to a renewed outbreak as the parasite is in its burrowing and re-production stage at which the medication has no effect.

Left untreated, about 15% of the released tomites will find and occupy a new host. This rather small number nevertheless accumulates to a 10 fold increase of parasites per week.

All fish are vulnerable and pose as potential hosts. Some species are more, some are less susceptible, depending on the slime coat and overall health of the fish.

Ich in nature is very rare and without the problems known in aquariums and closed aquatic systems. Due to the close confinement, Ich exploits the conditions of captivity in which it can easily spread. Most fish have a particular nightly resting spot from which the parasite moves off to form the cyst (the cyst building trophonts and the tomites released from them occur at night). Once freed from the cyst the tomites find a host ready in waiting.

The quarantine tank or a fish dip is the best preventative measure to avoid introducing the parasites by aninfected newcomer.

Once Ich breaks out, the main tank has to be treated. Several treatment options are commercially available and have to be used as directed. Treatments should be chosen based on the set up as active ingredients contain copper, formalin or malachite green by themselves or in combination. These can and will pose significant risks for plants, invertebrates and reef systems. Copper, if overdosed, lowers the fish’s’ resistance to fight off diseases, and can cause damage to liver and kidney.

For salinity insensitive aquatic environments, slowly lowering the salinity to 1.009-1.010 (specific gravity) for 14 days will extinct the parasite.

For more delicate plant and reef setups, reef safe treatments not containing above compounds have to be used.

ICK Lifecycle

An outbreak of serious ich will look like white grains of salt on the skin of your fish, from 0.3 to 1mm in diameter. Each individual spot is actually an adult parasite known as the trophont, which has been enveloped in the pus and tissue of the infected fish's skin and slime layer. Heavy infestations can be very dangerous if they reach the gills or cause secondary bacterial infections, so ich is definitely not a disease to be treated lightly. If allowed to progress to the point where the fish is very ragged in appearance and hanging near the surface, displaying a lot of respiratory distress, it can be fatal.
The white spots, however, only indicate one stage of ich (the only one that can be seen by the naked eye). After infecting the fish, the adult organism falls off into the gravel and becomes encysted in a free-living dormant stage known as a tomont. THIS CYST STAGE IS INVULNERABLE TO MEDICATIONS. This is the reason why a raise in temperature is suggested IN CONJUNCTION with ich treatments...it speeds up the life cycle and makes the stages that are treatable come around faster. If you do raise the temperature, do so very slowly so as not to stress the weak fish further.. raise it no more than 1-2 degrees every day, and do not allow this temperature to fluctuate. Also, consider the types of fish you are keeping... most tropicals can tolerate as high as 84-86 F, but most goldfish will start to languish in the high 70's, so don't push them any further.

Additional Info

News from the Warfront with Cryptocaryon irritans (Part 1 of 5) by Terry Bartelme

Saltwater Ich and Garlic - Aquarium Fish Diseases Ick, By: Terry D. Bartelme

Aquarium.Net Feb 97 Diseases in Fish, By Shawn Prescot

Marine Ick Part I, Steven Pro

Marine Ick, Part II, Steven Pro

Symptoms of Stress & Disease

An Old Cure for an Old Disease (Fishlore.com)

Freshwater Ich, White Spot Disease, By Bob Fenner

Protozoan parasites. (Skeptical Aquarist)

How to Identify & Prevent Saltwater Ich (Cryptocaryon irritans) (Liveaquari.com)



Good Luck!