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White Spot Disease?

White spot disease is a pathogenic disease commonly called “Ich” (1). The freshwater parasite is Ichthyophthirius multifiliis. The marine/saltwater parasite, which is morphologically and pathologically similar ciliate parasite is Cryptocaryon irritans (1).

Ichthyophthirius multifiliis has a large horseshoe-shaped macronucleus (1).

Cryptocaryon irritans has a large crescent-shaped, lobed macronucleus that is not horseshoe-shaped (1).

Both parasite have a similar presentation. They often can be grossly seen on the skin and fins, measuring up to 1mm (up to 0.5 mm in Cryptocaryon irritans) in size producing the appearance of small, white, raised bumps on the surface of the skin and fins (1, 3). Other times the infestation may only appear as small, nonspecific lesions where the parasite penetrates through the epithelium of the skin and fins (1, 3). Clinical signs you may seen include: congregating near water intakes, flashing (rubbing against the substrate and objects within the environment), increased opercular/gill rates, increased mucus production, lethargy, anorexia, ulcerations, and secondary bacterial/fungal infections (1, 3).

If you have gotten this far, your probably thinking this information isn’t anything new or ground breaking. Some may have read this for the first time and found this information new and helpful, which I hope is the case. Though, many hobbyist/aquarist are fairly knowledgeable and are accustomed to be weary of white spots on their fish.

I have noticed on various online forums and online posts discussions regarding white spot disease. The main concern I see - my fish has white spots, is this ich? My goal for this article isn’t to diagnose and discuss treatment. My goal is to bring awareness that not all white spots are necessarily ich. I always advocate to reach out to an aquatic veterinarian for diagnosis and treatment. But if you have started treatment and not getting the appropriate response as expected please reach out to one because you may be treating the wrong disease or need some adjustment to your treatment plan.

Here is a list of various causes of white spot lesions in fish. This list will include freshwater and saltwater ornamentals. Food and bait fish were noted included in this list and nor is this list exhaustive.

Light Spot Lesions that could be mistaken for White Spot Disease (1, 2, 3, 4):

  1. Infectious Inflammatory:

    1. Protozoa: Amyloodinium, scuticociliates (Uronema vs Tetrahymena)

    2. Viruses: Lymphocystis, carp pox, adenoviruses

    3. Bacteria: Mycobacterium, Nocardia, Edwardsiella, Flavobacterium, epitheliocystis

    4. Fungal or Fungi-like: oomycetes, microsporidian (Glugea spp)

    5. Metazoan: monopisthocotyle monogeneans, digenean metacercariae

    6. Myxozoa: Henneguya spp.

  2. Metabolic

    1. Calcinosis cutis

  3. Neoplasia

    1. papillomatosis, dermal sarcoma

  4. Normal anatomy

    1. Nuptial tubercles - male cyprinids during breeding season

  5. Life support system/environment

    1. Gas supersaturation

A dinoflagellate, Amyloodinium ocellatum in marine species and Piscinoodinium pillulare in freshwater fish is the cause of "velvet." This is also known as rust disease, gold dust disease, or coral fish disease in marine fish (4). Source Picture:

Nuptial tubercles or also known as breeding stars. These are usually found on the opercula and leading edge of the pectoral fins of male goldfish and koi (4). These are usually visible during breeding season and can measure up to 2mm (4). These are not insidious lesions, these are normal structures. Souce picture:

The idea of this list isn’t to be exhaustive but to allow you see that not all spots are equal. Most the time if you see white spots on a freshwater or saltwater fish the odds of it being Ich is probably high. Though I don’t want you to be too narrow minded to other potentially causes, especially if the fish aren’t displaying the typically clinical signs expected with Ich. If your fish are showing these signs or you have started treatment and no improvement please reach out to an aquatic veterinarian. Follow the links to find a fish vet in your area or contact me to help you find someone near you.

American Association of Fish Veterinarians:

World Aquatic Veterinary Medical Association:


- Robert Martinez, DVM, CertAqV


  1. Smith, Pedro A., Elliott, Diane G., Bruno, David W., and Smith, Stephen A. “Skin and Fin Diseases.” Fish Diseases and Medicine, edited by Stephen A. Smith, CRC Press, 2019, pp. 121-122.

  2. Hadfield, Catherine A. “Cutaneous Signs." Clinical Guide to Fish Medicine, edited by Catherine Hadfield and Leigh Clayton, Wiley-Blackwell, 2021, pp. 326-328.

  3. Hadfield, Catherine A. “Protozoal Diseases." Clinical Guide to Fish Medicine, edited by Catherine Hadfield and Leigh Clayton, Wiley-Blackwell, 2021, pp. 483-491.

  4. Wildgoose, William H. “Skin disease." BSAVA Manual of Ornamental Fish 2nd Edition, edited by William H. Wildgoose, British Small Animal Veterinary Association, 2001, pp. 115-116.

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Tin Nguyen
Tin Nguyen
Jan 14, 2023

Thank you Dr. Martinez for posting the differential rule outs for "white spots" on fish. Really love looking at the macronucleus on cytology!

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