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Ichthyophthirius multifiliis (Ich) in Freshwater Fish

Ichthyophthirius multifiliis (Ich) in Freshwater Fish

Updated on February 03, 2023
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Reviewed by Don Spaeth
Petco’s National Aquatic Care, Education and Programs Manager

Not unlike us, fish can feel a little under the weather from time to time. Just like diseases and infections we encounter, fish can also contract diseases ranging from bacterial, fungal and parasitic. One disease that aquarists may encounter is a little common parasite referred to as “ich” or white spot disease.

Understanding and Identifying Ich:

This disease is one of the most encountered within the aquatic hobby, found in both freshwater and marine environments. Freshwater ich is cause by the ciliated protozoan Ichthyophthirius multifiliis and Cryptocaryon irritans can wreak havoc in marine. Many diseases can be difficult on the fish and aquarist, but these parasites can be downright frustrating due to their complex life cycle.  

There are a couple life stages to these parasites. This consists of the parasitic trophozoites which matures in the skin/gill of the fish into the trophont (mature tophozoite). After 3-7 days the trophont drops from the fish, called a protomont and settles onto an area within the aquarium like the substrate. At this time, the protomont is now referred to as a tomont and begins cell division, aka mitosis. Each tomont can produce 100 to 1000 tomites. These tomites typically hatch within 3 to 14 days but can stay dormant for around 70 days. The tomites hatch out into free swimming theronts in search of a fish to attach to and feed off of. The reproductive process is temperature dependent and can be slowed or increased based on how cool or warm the water is. They need to find a host within 2 to 3 days or they will die. Once they find a host the theront can burrow into the basal layer of the gill or skin epithelium within a few minutes developing into a trophont, starting to process all over again.

What make these parasites troublesome is it only takes one parasite to start the cycle and cause havoc. The parasite tends to start out in the gill and may go unnoticed until it drops off, multiplies, and starts to reinfect the fish. 

The most obvious symptom of ich are the infamous white spots on the body, fins, and gills. Some other early identifiers of the disease being in the gill are rubbing, aka flashing, against items within the tank. The fish may show signs of respiratory distress, refusal to eat, and can potentially lead to death if left untreated.

Prevention and Treatment:

Preventing ich from entering your aquarium is the best way to combat this pesky disease.  

Many diseases are stress driven so reducing stress in the aquarium is one of the best ways to prevent disease from entering the aquarium, thus keeping your aquatic life safe. Ensure your water quality and temperature is being maintained within healthy parameters, keeping nutrients low by performing routine water changes. Balanced nutrition aids in keeping the aquatic life’s natural immune system strong and providing an abundance of hiding places will help prevent territorial battles which can contribute to a stressful environment. 

Quarantining new aquatic life, including plants or coral, in a separate aquarium is one of the best ways of reducing the chance of introducing disease into your aquarium. This can be a small aquarium setup with no substrate, some hiding areas, and simple filtration adequate for maintaining the aquatic life safely for 4 to 6 weeks.  By quarantining you will be able to safely administer treatment in the event that a parasite is identified.  

Early detection is key. If a parasite makes its way into the aquarium and you have positively identified it, immediate treatment is critical to increase a successful recovery.  

What makes ich a little more difficult to treat is that only the vulnerable free-swimming stage of the parasite is treatable with medications. The best way to approach treatment, for either freshwater or marine fish, is to setup a quarantine “hospital” tank and treat that system.   This will allow the main system to remain empty and eliminate the parasites’ food source, causing them to die off. 

For freshwater ich, slowly increasing the salt content with 1 Tbsp per 3 gallons of aquarium water or slowly lowering the specific gravity to 1.009-1.010 for marine fish for 14 days within the quarantine tank as well as raising the temperature to @82 degrees have shown beneficial effects in combating this parasite.  

There are also several medications available such as copper, formalin, and malachite green. Some medications can and will pose significant risks for scaleless or sensitive fish, plants, invertebrates, and corals. There are some risks with certain medications, for example, copper sulfate can become toxic if overdosed. Copper also lowers the fish’s natural immune system and can cause damage to the kidney and liver. Always follow the manufacturer’s instructions when administering any medications


Immune System:

Fish that survive an ich infection may develop an immune response and become resistant to re-infection. These fish contain antibodies within their mucus and serum that can assist against the parasite. When the infective theronts encounter these antibodies, they inhibit the theronts ability to swim, causing them to become immobilized and preventing them from attaching to the fish. 

For additional information on addressing and treating ill aquatic life, please visit your neighborhood Petco Pet Care Center and talk with one of our aquatic specialists. 

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