If your fish has cloudy, velvet-like skin and appears as though sprinkled with icing sugar, this is an indication of velvet disease (Piscinoodinium). Learn everything about this condition and what it means for your fish.
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Velvet disease is a highly contagious fish illness, so swift action is crucial.
Velvet disease is a highly contagious fish disease. It affects fish of all species regardless of age and, if not treated, leads to a slow death of the affected animals. To prevent all fish from becoming infected, you should take immediate action and isolate those affected.
Initially, the parasite Piscinoodinium pillulare only affects the gills. After a few days, it spreads over the entire skin surface.
You can then typically observe the following physical changes in your fish:
Affected fish often exhibit altered behaviour. Aquarium inhabitants suffering from velvet disease frequently stay at the water surface, on the bottom, or near the filter outlet or hide. Moreover, they often rub against the bottom and objects.
In addition, affected animals often refuse food intake, leading to weight loss. Listlessness or clamping of the fins (“fin rot”) may also sometimes be observed.
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Diagnosis of velvet disease is made after a comprehensive discussion with the owner, a thorough general examination, and the recognition of specific symptoms.
In larger fish populations, pathological-anatomical, bacteriological, and parasitological examinations are also advisable.
Specifically, the parasite Piscinoodinium pillulare can be detected microscopically in smear and compression preparations. Since it is hard to distinguish from mucous membrane cells, it is difficult to recognise in a swab.
If several animals are affected, it can be useful to take water samples for analysis in a laboratory.
Since the parasite Piscinoodinium pillulare possesses photosynthetic properties due to its chloroplasts, treatment of the fish takes place in the dark.
Special antiparasitic drugs are helpful in treating an infestation of the parasite. Effective medications against Piscinoodinium pillulare include quinine hydrochloride, copper sulphate and substances with 2-amino-5-nitrothiazole.
Always seek the advice of a knowledgeable veterinarian. Some fish species, such as catfish, are sensitive to certain medications, as are lower organisms like snails, mussels, and shrimp.
Generally, you should treat sick animals in a quarantine tank and observe the remaining fish for signs of illness. Only return the fish to the aquarium or pond when they have fully recovered.
To provide support, you can also add some cooking salt (approx. one gram of salt per litre of water) to the tank. However, tolerance must be clarified before doing so.
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The costs for treating velvet disease cannot be precisely estimated in advance. They always depend on the size of the fish population, the examinations, and the medications used.
Velvet disease leads to a slow, painful death of all affected fish if not promptly treated. However, if caught early, it is curable.
Fish that are already severely affected (velvet covering) and suffering should be humanely euthanized without stress and pain.
Velvet disease, also known as Oodinium infection, Oodinosis, coral fish disease, Pillularia disease, or Colisa disease, is caused by the parasite Piscinoodinium pillulare (dinoflagellates) in freshwater and Amyloodinium ocellatum in saltwater.
The parasites infect the skin and gills, damaging them with root-like plasma threads and ultimately dissolving them.
The development and life cycle of P. pillulare is highly temperature dependent. In colder water, the development takes longer than in warm water.
To accelerate the life cycle of the parasite, the water temperature can be increased. However, in infected fish, there is then the danger of dying from a lack of oxygen due to massive proliferation in the gill tissue.
In the initial stage, only the gills are affected and cause significant respiratory distress. The rest of the fish’s skin may still appear completely free of parasites.
When P. pillulare leaves its cysts, it spreads creepingly over the entire skin surface. In an examination from a front diagonal perspective against the light, this leads to cloudy skin that appears sprinkled with icing sugar. In a severe infection, the skin appears velvet-like and the coating has a yellowish to brownish hue.
The disease’s progression is often difficult to recognise at first. In advanced stages, the massive spread of the parasite then leads to tissue breakdown and the skin peeling off in shreds. In addition, there are internal bleedings within the gill filaments.
To prevent velvet disease from occurring in your aquarium, you should always have newly purchased fish checked for the parasite.
Place new arrivals in a quarantine tank for better observation for four to six weeks during the initial phase. Invertebrates, crustaceans, and tank items can also bring the cysts into your tank.
This article from zooplus Magazine is purely informative. If your pet is experiencing discomfort, contact your veterinarian for diagnosis and treatment.
I studied veterinary medicine at LMU Munich, where I also finished my PhD in 2012. After that, I was able to gain a lot of experience, for example as a practicing veterinarian and scientific advisor. Particularly important to me is the continuous improvement of animal welfare and farm animal medicine. My greatest concern has always been to act in the best interest of my patients and to provide them with optimal care. In addition to my veterinary knowledge, I am happy to share my experience as a horsewoman and long-time dog owner, as well as a dog sportswoman.
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