Marine Ich, Cryptocaryon irritans, is a common fish disease caused by an external parasite. Once a fish is infected, small white cysts on the skin, fins and inside of the gills may be visible. The infected fish may breathe rapidly or quickly rub its body on objects in your tank.
Marine Ich preys upon fish by burrowing into the flesh and gills and can cause extensive damage. It can quickly turn lethal when the parasite clogs the fish's gills, preventing respiration. This parasite is difficult to treat inside an aquarium because it goes through several different life cycles. Repeat infections are common. With a little understanding of Marine Ich's life cycle, it will be much easier to effectively treat and rid your aquarium of this parasite.
The life cycle of Marine Ich consists of four unique stages in which the parasite takes on five different forms:
During each stage the parasite performs a different function that helps ensure the parasite's survival.
The free swimming Theronts search for a host to prey upon. This is a sensitive stage for the parasite because if it does not find a host within 48 hours, it will starve and die. This is the stage at which the parasite can be effectively killed with medication. During all other stages, the parasite is too well protected to be treated with known Ich medications.
Once the Theront finds a host, it attaches and is now called a Trophont. The Trophont burrows into the fish and consumes the flesh. This is the stage at which infection is evident as little white salt sized dots on the fish's skin.
3) Drop Off
After 3-9 days of feeding, the Trophont releases from the fish and is known as a Protomont. During this brief 2-8 hour time frame the parasite moves onto the substrate to begin reproducing.
Once embedded in the substrate, the parasite—referred to as a Tomont—starts to form anywhere from 200 to 1000 (or more) child cells, called Tomites, inside its walls. This is the stage at which many hobbyists are fooled into thinking they have defeated Ich. The parasite can live on your substrate from 3 to 72 days with no obvious signs of infection on your fish. The Tomont restarts the life cycle once it hatches and releases child cells into the water column to search for another victim.
An ounce of prevention is worth a pound of cure when it comes to Ich. Properly isolating and observing new fish for 4-6 weeks will really help to avoid introduction and widespread infection in your tank.
Feeding highly nutritious foods to ensure proper nutrition will really help your fish survive an infection.
Although Ich is a very common parasite, wild fish are generally not seriously threatened by Marine Ich because the chance of encountering the parasite in large numbers is far less in the wild. In captivity, once the parasite is in your tank, the fish are trapped and constantly exposed to the parasite resulting in rapidly spreading infections.
Treatment for Marine Ich has been widely documented and studied in aquarium circles. Medications, hypo salinity, UV Sterilizers and increasing water temperature have been proven beneficial in reducing the severity of Ich infections, but they are not always 100% effective due to the life cycle and nature of this parasite.
Corals and invertebrates are not susceptible to Ich, but are highly sensitive to many of the medications that treat ich, which is one of the main reasons it is important not to introduce Ich into your tank in the first place.
The best way to eradicate this parasite from your aquarium and prevent further infection is to remove and isolate all of your fish from the tank. Treat the isolated fish with medication in a separate tank and keep them isolated for 4-8 weeks. Once the parasite is not able to find a host in your main tank, it will completely die off after a minimum of 4 weeks.