All About Marine Ich and Other Fish Parasites

Ocellaris Clownfish and Anemone

Mikael Kvist/Getty Images

Learn all about how to diagnose and treat the many types of saltwater parasites that can plague and kill marine fish in aquariums, such as White Spot (Marine Ich), Black Spot, Velvet and Clownfish Diseases, as well as other parasites like fish flukes. As with most types of parasitic diseases, time is of the essence in detecting, diagnosing and treating the affected fish.

  • 01 of 07

    Clownfish Disease (Brooklynella hostilis)

    An infestation of Brooklynella hostilis is commonly known as Clownfish Disease, and although this type of saltwater ciliated protozoan is usually associated with Clownfishes as the name implies, it is still a parasitic organism can affect other species, such as Angelfishes. Brooklynella feeds on dead skin cells and can cause severe damage to gills. The gills may be swollen, and the fish may have irregular breathing. Other signs include sloughing of skin, and congestion of the gills. The parasite reproduces by binary fission and spreads rapidly, and can easily transfer from fish to fish. Formalin is an effective treatment.

  • 02 of 07

    Saltwater Ich (Cryptocaryon irritans)

    White Spot Disease, or Saltwater Ich, is caused by an infestation of the ciliated protozoan I multifiliis. Even though this organism progresses less rapidly than Oodinium and Brooklynella, in a closed aquarium system it can reach overwhelming and disastrous numbers just the same if it is not diagnosed and treated properly upon recognition. The signs of the ich parasite infestation typically include ragged fins, scratching on rocks, and white spots on the gills, fins, and body of the fish.

  • 03 of 07

    Saltwater Ich (Cryptocaryon Irritans)

    Diagram of the 4-stage life cycle of Cryptocaryon irritans, commonly known as Saltwater Ich or White Spot Disease.
    Stan Hauter

    Cryptocaryon irritans is probably the most common type of parasitic outbreak encountered by saltwater aquarium keepers. The 4-stages of this organism's life cycle are simply outlined here, including a diagram, which will help you better understand the different phases of life of White Spot Disease, especially when it is most vulnerable 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

    Marine Velvet (Coral Fish Disease)

    Marine Velvet, or Coral Fish Disease, is caused by an infestation of the single-celled dinoflagellate ​Amyloodinium ocellatum. The life cycle of Amyloodinium follows a three-stage growth model, maturing from a feeding trophont to a reproducing tomont, before becoming a free-swimming dinospore that attaches to a new host fish. Amyloodinium reproduces rapidly and can easily go undetected, as visual signs of its presence are typically not apparent until it's too late. The skin of fish that have been infested with Amyloodinium has a powdery or velvety appearance. Other signs include a loss of coordination and sporadic gasping. It is not unusual for an infestation to cause a total fish population wipeout, so knowing what symptoms to look for to diagnose it as soon as possible, as well as which treatments are most effective for eradication, are critical.

    Continue to 5 of 7 below.
  • 05 of 07

    Black Ich, Black Spot, or Tang Disease

    Black Ich, or Black Spot Disease, is actually an infestation of tiny Paravortex turbellarian flatworms, and even though the name Tang Disease implies it is usually associated with Tangs and Surgeonfishes, it can affect other fish species. Signs of this disease are black spots caused by embedded flatworms in the skin and fins of affected fish. Although the worms are rather easy to get rid once they appear as black dots on fish, they can survive for several months without a host, and therefore can be difficult to eliminate from an aquarium.

  • 06 of 07

    Top Parasite Medications

    Parasitic infestations in a saltwater aquarium are among the most feared and difficult to treat. There are a number of medications on the market designed to prevent and/or eliminate parasites. Some can be used with invertebrates, some cannot. Freshwater dips, hyposalinity treatments, formalin and copper are treatments commonly used for saltwater parasites.

  • 07 of 07

    Using Formalin

    Kordon's Rid-Ich

    Over-the-counter formalin products, typically made up of a 37 percent solution of formaldehyde diluted in water, are one of the most effective medications for treating various types of protozoa infestations (Cryptocaryon and Brooklynella), parasitic fish flukes, lice, worms (black ich), and fungal diseases. Find out how to use formalin in many different ways to safely treat diseased fish, such as by means of a quick 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.
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  1. Parasitic Diseases of Fish. Merck Veterinary Manual

  2. Fish Parasites & Diseases. Indiana Department of Natural Resources