Velvet disease (oodinium)

Recognise and cure velvet disease in fish

Description of velvet disease

Oodinium is a microscopic parasite that is both animal and plant like at the same time. It can photosynthesise when under bright conditions much like algae but can also feed off fish as a parasite.

It is similar to white spot (ich) in that it has a free swimming stage and an attachment stage. It is dangerous to new fish when it is in the free swimming stage. It swims around until it can attach itself to the fishes skin/scales or the fish’s gills. Once it attaches, it sends out root like tentacles deep into the fish’s flesh. Once planted into the fish, ite never moves, it then feeds off the fish and grows.

This infection and penetration of the fish causes an allergic reaction in the fish. The fish’s skin swells and bleeds.

Lifecycle description of velvet disease

The oodinium parasite grows on the fish and when it becomes full size, it withdraws its tentacles. It then forms a protective cyst around itself and falls off the fish, onto the substrate or aquarium floor. At this point it gets ready to reproduce, by dividing itself over and over until there are over 200 spores. These spores become dinospores which hatch out and then swim around seeking a new host, perpetuating the whole process.

The lifecycle of the oodinium is about 10 days but can be faster at higher temperatures and slower at lower temperatures. Note that the newly hatched oodinium must find a host to feed off within 14 hours or they die.

Because of the rapid lifecycle of the oodinium, infestations can build up rapidly and cause heavy fish losses. So quick identification and medication is called for.

Finally, because of the oodinium’s ability to photosynthesise, bright lights actually make this condition worse. When an outbreak occurs dimming the lights can help your fish’s survival rates while you are medicating.

Some fish are better able to resist velvet infestation. However, marine fish such as clown fish and freshwater fish such as anabantids, goldfish, white cloud mountain minnows and killifish are very vulnerable to velvet.

Diagnosis of velvet(oodinium)

Velvet is recognised by the fish scratching themselves against objects and the skin or fins having a light dusting of grey/green or brown velvety texture on them.

Since velvet will get into the lungs, the fish will suffer from laboured breathing with flared gills. Often an excess of mucous is produced from the skin where the fish’s body mucous tries to flush off the irritation without success.

When the parasite drops off the fish, bloody areas and ulcers can be seen on the fish’s skin. It is not only fish that can be infected but other aquatic creatures such as newts, salamanders and other amphibians too.

Treatment of velvet(oodinium)

There are home based remedies and shop medicated remedies. The home based remedy consists of raising the aquarium temperature to 32C, turning off the light and medicating with salt and copper suphate. You can also immerse the fish for a few hours in a salt and copper sulphate bath.

Shop based medication can be bought and treat in the aquarium at the dosage as per instructions. Some fish that have a heavy infection with velvet and are very sick might not survive a salt bath or very high temperatures so off the shelf medication might be the only option. On saying that raising the temperature a few degrees and cutting out the light will not harm very sick fish.

Medication is usually effective in eradicating the velvet disease. But, sometimes the parasite can persist because it is capable of infecting the intestines and be protected from medication. Also, the encysted state of the oodinium is very resistant to chemicals.

Only when the organism leaves its encysted state can the chemicals be effective. But all the oodinium will not conveniently leave its encysted state when you medicate. So you must re medicate at 3 and 7 days to catch all the velvet organisms when they leave the encysted state.

Finally, because of the damage caused to the skin by the velvet, secondary bacterial and fungal infections often set in. Treat with appropriate anti bacterial and anti fungal medication.



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