Velvet Disease

Disease Type: Parasitic skin flagellate

Description

The name sounds nice, but don't be fooled. Velvet is one of the more common diseases in aquarium fish, and can strike down every inhabitant in the tank before the hapless owner realizes what he or she is dealing with. Also known as Rust or Gold Dust disease, it is caused by one of several species of a tiny parasite known as Oödinium. Oödinium is a dinoflagellate - a creature that is classified by some as a protozoan, and by others as algae because it contains Chlorophyll. Oödinium doesn't care how it's classified - it's an equal opportunity parasite, striking both freshwater and saltwater fish alike. In freshwater fish either Oödinium pilularis or Oödinium limneticum causes Velvet disease. In marine fish Oödinium ocellatum causes the dreaded Coral Fish disease.

All three species have symptoms and lifecycles that are similar to the well known parasite, Ich. Oödinium produces white pustules on the fish, however they are much finer than the spots seen in Ich - so fine that they are sometimes not seen before the fish perishes. Like Ich, Oödinium is present in most commercial tanks, but only becomes a problem when the fish are stressed by poor quality water, changes in the water temperature, or being transported.

Velvet has a similar life cycle to Ich. Once it has found a host the parasite initially adheres by using its flagellum. It then forms rod like appendages called pseudopodia, which penetrate the skin and soft tissues of the gills. These pseudopods destroy the cells and feed on the nutrients contained in them. After feeding and maturing sufficiently, the parasite drops off the fish and begins to divide into dozens of new flagellated cells that are released into the water to seek hosts. The new cells must find a host within 24 hours, or they will die.

Symptoms

  • Scratching against hard objects
     
  • Fish becomes lethargic
     
  • Loss of appetite and subsequent weight loss
     
  • Rapid, laboured breathing
     
  • Fins clamped against body
     
  • Fine yellow or rusty coloured film on skin
     
  • In advanced stages skin peeks off

Unfortunately the disease is often advanced before the appearance of the distinctive "velvet" on the skin. Initially the fish will rub against hard objects in an attempt to dislodge the parasites. As the disease progresses the fish becomes lethargic, the fins are held close to the body, appetite is reduced and the fish will lose weight. A key symptom of the disease is difficulty in breathing, resulting in rapid gilling.

Perhaps the most telltale symptom is the appearance of a velvety film on the skin that resembles gold or rust coloured dust. The film may be difficult to see, but can be more easily detected by directing a beam of a flashlight on the fish in a darkened room. The parasite is most often seen on the fins and gills. As Oödinium destroys more tissue, pieces of skin will literally peel away.

Velvet attacks all fish and will even affect fry that are only a few days old. Anabantoids, danios, goldfish, zebrafish, and killifish are particularly susceptible to velvet disease.

 

Treatment

  • Raise water temperature
     
  • Dim lights for several days
     
  • Add aquarium salt
     
  • Treat with copper sulphate for ten days
     
  • Discontinue carbon filtration during treatment

Because Velvet is highly contagious and usually far advanced before being diagnosed, it is important to take steps to treat it as soon as possible. Treatment is targeted at the free-swimming stage of the parasite. Copper sulphate is the treatment of choice. It should be used according to the manufacturers instructions for a full ten days to ensure that the parasite is completely eradicated. Atabrine (Quinacrine hydrochloride) is another medication that can be used to treat Velvet.

Because Oödinium is dependant on light, dimming the aquarium lights aids in eliminating the infestation. Increasing the water temperature to 82°F will speed the process, and adding salt to the water will ease the labored breathing caused by destruction of gill tissue. As with any treatment, activated carbon should be removed from the filter, as it will remove the drugs from the water

 

Prevention

  • Quarantine new fish for two weeks
     
  • Maintain high water quality
     
  • Provide fish with a nutritionally balanced diet

Velvet usually only arises when poor aquarium conditions prevail and is highly infectious. Quarantine of new fish for two weeks will greatly reduce the likelihood of contaminating a healthy established aquarium. Any fish that appear to be ill should immediately be removed and kept in a hospital tank to avoid the spread of the parasite.

Source: http://freshaquarium.about.com/library/weekly/aa021002a.htm