Ich in Freshwater Fish

Causes, Treatment, and Prevention

Ichthyophthirius multifiliis white spot treatments for fish

The Spruce / Kaley McKean

Ich is a parasite caused by the protozoan Ichthyophthirius multifiliis. Ich penetrates a fish's skin or gills and creates small white spots on the body. The parasite multiplies and spreads to other fish quickly and is fatal if untreated. In addition to the white spots, symptoms include the fish scratching against surfaces in its tank and swimming close to the surface of the water due to difficulty breathing. Several treatments are available, and the prognosis is good for fish who receive treatment quickly. Consult an aquatic veterinarian to discuss the right care for your fish. You can largely prevent ich by maintaining proper tank hygiene and quarantining new fish before introducing them to your existing tank.

What Is Ich?

Ich, also known as white spot disease, is caused by the parasite, Ichthyophthirius multifiliis. Ich is usually visible as a small, white spot on your fish's skin. The ich parasite penetrates the skin or gills, burrows under the surface, and eats at the fish's flesh. Ich has a high mortality rate and is very infectious. If your tank contains multiple fish, all of your fish are likely infected. Once your fish is infected, it will develop the white, raised blister spots at the site of the parasite's penetration, and the parasite will rapidly multiply. After feeding on the fish, the parasite will detach itself and hatch into thousands. The life cycle of ich is temperature-dependent, with fewer days between stages of growth in warmer water and greater delay in colder water. Ich is especially prevalent in aquariums.

Symptoms of Ich in Freshwater Fish

Ich can be mistaken for other, less severe issues. Monitor your fish's symptoms carefully and consider environmental factors before diagnosing.


  • White spots
  • Scratching
  • Hiding
  • Surface swimming
  • Sudden death

White Spots

The white spots on your fish's body will likely be the clearest sign of an ich infestation. The spots can range from the size of a pinprick to a grain of sugar. On the first day of noticing the spots, your fish may only have a handful, and the next day, the number could have quadrupled. Some fish develop white spots from stress, not ich. So if the number of spots on your fish doesn't increase as the days go on, it may be from stress and not ich.


If you notice your fish rubbing up against items in your tank, such as decorative rocks, it may be scratching an uncomfortable itch caused by the parasite. As a result of the scratching, your fish may lose scales, which could indicate the presence of a parasite.


Because of survival instinct, your fish may hide when uncomfortable or stressed. If this is normal behavior for your shy fish, there might not be an issue, but if this is abnormal, consider ich a factor. The discomfort caused by ich could be enough to trigger this response.

Surface Swimming

If ich gets into your fish's gills, it could cause issues with breathing, leading to surface swimming to search for more oxygen.

Sudden Death

Ich is a leading cause of sudden death in fish. If you notice many of your fish dying in a short period, there is likely a parasite at play. If untreated, ich can have a 100% mortality rate.

Causes of Ich

There are several ich causes, but you can drastically lower the chance of infection with proper hygiene measures.

  • Failure to quarantine new fish: The most common cause is failure to quarantine a new fish addition before introducing it to an aquarium. Even if a fish doesn't have spots, it's good to quarantine it before transferring it between tanks. Fish can carry ich in dormant stages and may not become symptomatic until introduced to other fish.
  • Improper sanitation of equipment: It's important to properly sanitize your aquarium thoroughly and frequently, especially when adding new decor or filtration. Ich can be carried on fish as well as surfaces.
  • Compromised immune system: While not a direct cause, your fish is much more likely to become infected by ich when its immune system is compromised. Its weakened immune system could be because of stress.

Diagnosing Ich in Freshwater Fish

You can usually safely diagnose ich based on the white spots on your fish's skin. Still, the suspected parasite will need to be examined under a microscope for a definitive diagnosis. An aquatic vet will take a small skin scrape sample from your fish, or a small piece of tissue will be clipped from the gill or fin for analysis.


There are several treatment options for fish with ich. You may use prescription medications or non-prescription herbal treatments, including garlic juice, to treat ich, but consult with an aquatic veterinarian to confirm the best option for your fish. Medical or herbal remedies can be harmful to some fish and effective for others. You can also add substances like hydrogen peroxide to your tank, but it will only be effective on ich in its earlier stages.

Monitoring and maintaining proper water temperature is critical to ensure the parasite is completely eliminated from your system. Many online forums recommend manipulating your tank temperature to speed up or immobilize ich, but it's essential to be extremely careful in doing this to avoid inflicting stress on your fish, weakening its immune system. Heat manipulation can be effective, but not on all breeds. Additionally, putting an infected fish in a clean tank will help keep it from becoming reinfected.

Prognosis for Freshwater Fish With Ich

If untreated, ich will almost definitely kill the infected fish and spread rapidly to others, causing mass mortality. Ich must be considered an emergency and eradicated immediately.

If your fish receives treatment for ich swiftly, the prognosis is good. Your fish will likely heal within a month and develop nearly complete immunity to the parasite.

How to Prevent Ich

While there is no sure way to prevent ich, you can take steps to limit the chance of an infestation.

All new additions of fish, invertebrates, decor, plants, and equipment should be quarantined in a separate tank using separate equipment for four to six weeks to help prevent the spread of ich. The quarantine period will be slightly shorter at higher temperatures. Do not manipulate your fish's ideal temperature range to shorten your quarantine period. This can cause stress to your fish and make them susceptible to other diseases and parasites. Keeping your fish in good health with a robust immune system helps prevent ich.

The ideal way to prevent ich in fish is with a vaccine. Unfortunately, there is no commercial vaccine available, but scientists are identifying vaccine candidate proteins that could lead to a vaccine in the future.

  • Will ich kill my fish?

    If ich is untreated, it will almost certainly kill your fish and spread to others, resulting in mass death. Treat ich immediately after noticing it to avoid this.

  • Are there any natural remedies for ich?

    Natural, herbal remedies for ich include garlic juice. You can also add a small amount of salt to the water to recover a fish's natural slime coat.

  • Is ich the same thing as white spot disease?

    Ich is the same thing as white spot disease. Ich is the shortened version of the scientific name of the parasite that causes white spot disease.

Article Sources
The Spruce Pets uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Ichtyhophthirius (White Spot) Infections in Fish. University of Florida.

  2. von Gersdorff Jørgensen et al. Approaches towards DNA vaccination against a skin ciliate parasite in fishPloS one7(11), National Library of Medicine. doi:10.1371/journal.pone.0048129