Marine Ich

Marine Ich, also known as White Spot Disease, is a common parasitic disease that affects saltwater fish. It’s caused by the ciliate protozoan parasite and Cryptocaryon irritans, which attach themselves to a fish’s skin and gills.

Marine Ich is very contagious and can spread quickly through an aquarium. It’s often introduced into an aquarium through new fish or contaminated equipment. Poor water quality and stress can also weaken a fish’s immune system, making them more susceptible to the disease.

Symptoms of Marine Ich

Symptoms of Marine Ich include:

  • White spots on the skin and fins of infected fish
  • Rubbing against objects in the aquarium

As the disease progresses, fish can become lethargic and lose their appetite.

Diagnosing Marine Ich

Diagnosing Marine Ich isn’t hard if you see white spots all over their bodies and notice their behavior change. A veterinarian or aquatic specialist might also examine a skin scraping under a microscope to confirm the presence of the parasite.

Stages of Marine Ich

Marine Ich has several stages in its life cycle, which can help with understanding the progression of the disease:


The parasite begins as a free-swimming tomont, searching for a host to attach itself to.


Once it finds a host fish, the tomont attaches itself to the skin or gills and burrows into the fish’s tissue.

Feeding and Maturation:

The parasite feeds on the host’s tissue and undergoes maturation, which can last up to 10 days.


After maturation, the parasite detaches from the host and releases hundreds of free-swimming offspring. These offspring continue the cycle by searching for a new host to infect.

Treating Marine Ich

There are several treatments for Marine Ich, but the best approach is to treat all fish in the aquarium at the same time to prevent re-infection. Here are some common methods used to treat Marine Ich:

  • Medications: There are several medications available that can be added to the aquarium water to kill the parasite. These include copper-based medications, formalin, and malachite green.
  • Hypo-salinity: Lowering the salinity level of the aquarium water can also be an effective treatment for Marine Ich. This involves gradually lowering the salinity over several days until it reaches a level that is too low for the parasite to survive. If you have an unused aquarium you can also use this as a dipping tank so that you can keep your normal aquarium water conditions unchanged.

Preventing Marine Ich

Preventing Marine Ich is key to keeping your fish healthy and avoiding the spread of the disease. Here are some tips for preventing Marine Ich:

  • Quarantine new fish: Always quarantine new fish in a separate tank for at least two weeks before adding them to your main aquarium.
  • Clean equipment: Clean any equipment that has been used in another aquarium before using it in your own tank to prevent the spread of disease.
  • Maintain water quality: Regularly test and maintain proper water quality levels in your aquarium, including temperature, pH, and salinity levels. Poor water quality can weaken a fish’s immune system, making them more susceptible to disease.
  • Feed your fish a balanced diet: Provide your fish with a balanced diet that meets their nutritional needs to help boost their immune system and overall health.