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 the supply 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 waste, 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.