Everything You Need to Know About Marine Ich and Other Fish Parasites

Ocellaris Clownfish and Anemone

Learn how to identify and cure the several saltwater parasites that can afflict and kill marine species in aquariums, including White Spot (Marine Ich), Black Spot, Velvet, and Clownfish Diseases, as well as other parasites such as fish flukes. Time is of the essential in identifying, diagnosing, and treating the infected fish, as it is with most parasite infections.

  • 01 of 07

    Clownfish Disease (Brooklynella hostilis)

    Clownfish Disease is caused by an infection of Brooklynella hostilis, and while this form of saltwater ciliated protozoan is most typically linked with Clownfishes, it is still a parasitic organism that may affect other species, such as Angelfishes. Brooklynella feeds on dead skin cells and can harm gills severely. The gills may be enlarged, and the fish's respiration may be erratic. Other symptoms include sloughing of the skin and gill congestion. The parasite reproduces by binary fission and multiplies quickly, allowing it to readily transmit from fish to fish. Formalin is a good therapy option.

  • 02 of 07

    An infection of the ciliated protozoan I multifiliis causes White Spot Disease, often known as Saltwater Ich. Even while this organism spreads more slowly than Oodinium and Brooklynella, it can still reach overwhelming and dangerous levels in a closed aquarium system if it is not identified and treated appropriately as soon as it is discovered. Rough fins, scratching on rocks, and white patches on the gills, fins, and body of the fish are all indicators of an ich parasite infection.

  • 03 of 07


    The most prevalent sort of parasite outbreak experienced by saltwater aquarium caretakers is Cryptocaryon irritans. The 4-stages of this organism's life cycle are clearly summarized below, along with a graphic, to assist you better understand the various stages of White Spot Disease's life cycle, particularly when it is most sensitive to treatment.

    1. The feeding or trophont stage is where the parasites are embedded under the skin and gills of the fish to feed on the fish's tissue fluids. This causes the white spots visible on the fish.
    2. Once the trophont matures, it leaves the fish as a protomont, which falls to the bottom of the tank and in a few hours becomes a tomont, the reproducing cyst. One tomont divides into hundreds of new organisms, called tomites, or theronts. The shell of the cyst protects the parasite from treatments.
    3. After a number of days, depending on temperature of the water, the tomont cyst ruptures to release the infective free-swimming theronts, seeking a fish. The theronts have about 24 hours to find a fish or they may die. This stage is the only time that ich medications are effective against the parasites.
    4. When the theront attaches to a new fish it becomes the trophont and begins feeding and growing, and the cycle begins again.
  • 04 of 07

    The single-celled dinoflagellate Amyloodinium ocellatum causes Marine Velvet, also known as Coral Fish Disease. Amyloodinium has a three-stage life cycle, beginning as a feeding trophont and progressing to a reproducing tomont before becoming a free-swimming dinospore that attaches to a new host fish. Amyloodinium reproduces quickly and can go unnoticed for long periods of time since visual evidence of its presence are rarely seen until it's too late. Fish infected with Amyloodinium have a powdered or velvety texture to their skin. Loss of coordination and intermittent gasping are some symptoms. Because an infestation may wipe out an entire fish population, understanding what signs to look for in order to detect it as soon as possible, as well as which treatments are most successful for eradication, is crucial.

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  • 05 of 07

    Although the name Tang Disease indicates that it is generally linked with Tangs and Surgeonfishes, Black Ich, or Black Spot Disease, is really an infection of microscopic paravortex turbellarian flatworms, and it can afflict other fish species. Black marks on the skin and fins of infected fish indicate the presence of this illness, which is caused by flatworms buried in the skin. Although the worms are relatively straightforward to remove once they appear as black spots on fish, they may persist without a host for several months, making them tough to remove from an aquarium.

  • 06 of 07

    Top Parasite Medications

    In a saltwater aquarium, parasitic infections are among the most dreaded and toughest to treat. There are a variety of parasite-prevention and/or-eradication drugs available on the market. Some of them can be utilized with invertebrates, while others can't. Saltwater parasites are routinely treated with freshwater dips, hyposalinity treatments, formalin, and copper.

  • 07 of 07


    Over-the-counter formalin preparations are one of the most effective remedies for treating protozoa infestations (Cryptocaryon and Brooklynella), parasitic fish flukes, lice, worms (black ich), and fungal illnesses. They are normally made up of a 37 percent solution of formaldehyde diluted in water. Learn how to safely treat ill fish with formalin in a variety of ways, including a brief dip, a timed bath, or long-term in a QT.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.


"Parasitic Diseases of Fish. Merck Veterinary Manual", "Fish Parasites & Diseases. Indiana Department of Natural Resources" ;