Updated: Nov 14, 2021
The most important aspect of aquarium ownership is the health of your fish. Recreating ideal water chemistry, temperature and habitat go a long way to reducing stress, bolstering the immune system, and promoting vivid coloration.
However, just like with any living creature, fish can get sick even if you do everything right. One of the most common illnesses that can effect your aquarium is an infection of the parasite ichthyophthirius, or ich in freshwater tanks, and Cryptocaryon, or marine ich, in saltwater tanks. Below, we'll discuss how both types of ich come to be in your aquarium, what you can do to prevent them, and how to manage an infection if one breaks out.
The first step with diagnosing and treating any illness is to know thine enemy. Understanding the freshwater and marine ich parasites' life cycles and biology is crucial to effectively treating the resulting illness. This knowledge is a powerful tool you can use to troubleshoot any problems you may come across during treatment.
Both types of ich are classified as protozoan ciliates. Protozoans are an informal classification of small unicellular organisms, and ciliates means they have a bunch of little "hairs" they use for locomotion. They don't sound so scary now do they?
There are four main life stages of the ich parasites. They go through these four stages over a period of seven days to eight weeks depending on temperature. Higher temperatures speed up their lifecycle (Nielsen 2000). The first stage is the feeding form, called the trophont, which is visible to the naked eye as white spots as it protrudes from underneath the fishes skin. The trophant will feed on the host cells until it reaches a certain size, then leave the protection of the host and enter the free-swimming stage called the tomont. Within as little as a few minutes or over several hours, the tomont will settle on a surface and form a protective gelatinous cyst wall; this is the third stage, the tomocyst. Once settled, the tomocyst will reproduce several hundred daughter cells within the cyst wall. These daughter cells are the fourth stage, known as tomites. The tomites will then burst from the tomocyst and begin searching for a fish host.
The ich parasites are introduced to the aquarium as trophonts on an infected host or as tomonts (free-swimming stage) in the water. Even one tomocyst attached to one piece of gravel can cause a tank wide infection. The ease with which the ich parasites can be transferred, and their prolific nature, is why it is important to prevent an infection before treatment becomes necessary.
The best way to prevent an infection is to inspect the health of the tanks you are getting your fish from. If the fish have white spots on them, that is pretty obvious, but remember, the ich parasites have three microscopic life stages that cannot be seen. Only buy from reputable sellers and inspect the fish for general signs of health and vitality as these demonstrate strong immune systems. Some secondary signs of unhealthy fish to look for when diagnosing your own fish, or fish at the store, with ich are: lethargy (loss of appetite and sluggishness), clamped fins, rapid breathing, resting at the bottom or top of the tank, and rubbing their sides on the substrate or rocks (flashing). These are common symptoms because ich effects the hosts' respiration and osmoregulation (fluid balance).
If all looks good, you may still bring home a contaminated host, plant, rock, or even coral skeletal base. To prevent infection of your display tank you can quarantine the new specimen in a separate tank for at least 7 days at a minimum temperature of 77 degrees Fahrenheit. Treat the quarantine tank with sodium chloride (non-iodized salt) at 1 tablespoon per gallon and hydrogen peroxide at 1 mL per gallon. In a marine tank, use the same amount of hydrogen peroxide and slightly increase the salt levels by 1-3 ppt (Nielsen 2000).
If you don't have the means to set up a quarantine tank, then you can use these amounts of salt and hydrogen peroxide in your main tank at a minimum temperature of 77 degrees Fahrenheit, 75 degrees for a tank with sensitive invertebrates, for a minimum of 7 days.
Fishes' natural immune systems can resist the ich parasite, but only if the host is healthy and has fought off an ich infection before (Buchmann 2019). Ich can exist in an aquarium for some time without ever causing an infection if the fish are immunized and healthy. If you have done everything you can and you notice your fish become infected with an ich parasite it is important to begin treatment immediately.
The first step to treating ich is to safely raise the temperature to 77 degrees F over several hours. If you raise the temperature too quickly you will stress the fish and weaken their immune systems even more. The ich parasites' life cycle is heavily dependent on temperature. At 77 degrees F, the parasite will undergo all four stages in about 7 days. The life cycle speeds up at higher temperatures (Nielsen 2000), but go too high and you risk killing your fish and definitely your more sensitive invertebrates. Keep the temperature below 82 degrees with fish only, 80 degrees with invertebrates and no more than 78 degrees with cold water species. You want the life cycle to speed up, because only the tomont and tomite (free-swimming) stages are vulnerable to medication, the other two stages which cause the most harm and are responsible for reproduction are resistant and generally unaffected by medication, hydrogen peroxide and salt treatments.
The second step is to begin medicating. At this stage, it is wise to transfer all fish, infected or not, into a quarantine tank if you have sensitive invertebrates and plan to use heavier medications like malachite green, methylene blue , or copper sulfate. I do not recommend using these as it is a pain to remove all fish and these chemicals are carcinogenic. Instead, leave your fish where they are which reduces further stress, and medicate with 1 mL per gal of hydrogen peroxide and the directed dosage of garlic extract daily. Hydrogen peroxide is toxic to both the tomont and the tomite, while garlic juice has shown toxicity to the tomite stage. Additionally, increase your salt level by 1-3 ppt for saltwater tanks and by 1 tbsp per gallon for freshwater tanks. Remember to do this slowly over 24 hours, just like with the temperature increase. I do not recommend water changes as they cause further stress and do nothing to remove the parasite. However, if your ammonia or nitrite levels are above 1 ppm and 5 ppm respectively, and you must do a water change, don't forget to add more salt to the new water to maintain the increased concentration.
Continue this treatment for 7 to 14 days and wait for the parasite to longer be visible on any fish for at least 72 hours. The ich parasites are fast, and can reproduce and infect rapidly. You may lose some fish in the process, if this is the case, don't lose hope, just be sure to remove them quickly so they don't decay and contribute to elevated ammonia levels. After the all clear, stop dosing hydrogen peroxide, garlic, and sodium chloride to bring your levels back to normal after your next scheduled water change.
The only way to completely remove the ich parasites from your system is to remove all hosts until the parasite has run its course and dies off, or to medicate the entire system and destroy the parasite at its most vulnerable stages. I don't recommend giving individual fish medicated baths as it does nothing for the whole system, and further stresses the fish. However, in some cases, it may be advantageous to use a bath as the fish's immune system, once immunized, can more easily fight off a second infection (Buchmann 2019). Don't forget to also treat the whole system as well.
The bad news is that ich parasites are rampant and easily infect aquariums and fisheries systems all over the world. The good news is scientists are motivated world-wide to research new treatments, and most studies are leaning towards environmentally friendly herbal extracts that boost the fish's immune systems or are toxic to the parasite.
Nielsen, C.V., Buchmann, K. "Prolonged in vitro cultivation of Ichthyophthirius multifiliis using an EPC cell line as substrate." Diseases of Aquatic Organisms. 42 (3): 215-219. 2000.
Buchmann, K. "Immune response to Ichthyophthirius miltifiliis and role of IgT." Parasite Immunology. 42 (8). 2019.