The name sounds nice, but don’t be fooled. Velvet disease is one of the most common diseases found in aquarium fish and can affect all inhabitants of the aquarium long before the unfortunate owner realizes what’s happening. Known as rust and coral disease or gold dust, it is caused by one of several species of a small parasite known as Oodinium, also known as Piscinoodinium. Oodinium is a dinoflagellate, a creature classified by some as protozoan and by others as alga because it contains chlorophyll. It is not important how it is classified, because it is a parasite with equal opportunities that affects both freshwater and saltwater fish.
In freshwater fish, velvet is caused either by Oodinium pillularis or by Oodinium Limneticum. In marine fish, Amyloodinium ocellatum causes the feared Coral fish disease. All three species have symptoms and life cycles similar to the well-known Ich parasite.
Oödinium dinospore swims using the flagella to find a fish and attaches to it with pseudopodia that penetrates into the skin, fins, and gills. Pseudopodia destroys cells and the trophont feeds on nutrients from the inside. After feeding and maturing, it gives up the fish and forms a reproductive cyst, tomont, which divides into several hundred tomites that are released into the water to search for hosts. They have to find a host within 24 hours or they’ll die.
Oodinium produces much finer golden spots than the spots seen at Ich. In fact, they are so fine that they are often not seen before the fish dies. Like Ich, Oodinium can be present in most commercial aquariums, but it becomes a problem only when fish are stressed by poor quality water, changes in water temperature, or when transported.
Initially, the fish rubs against hard objects in an attempt to get rid of parasites. As the disease progresses, the fish becomes lethargic, keeps its fins close to the body, loses its appetite, and will lose weight. A key symptom is a difficulty in breathing, which leads to faster infection.
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Perhaps the most obvious symptom is the appearance of a velvet-looking aspect on the skin of fish that resembles gold or a colored rust powder. The aspect can be difficult to see, but it can be more easily detected by directing a beam of light or a flashlight over the fish in a dark room. The parasite is most often seen on the fins and skin, but it can also infest the gills. Velvet attacks all fish and will even affect fish that are only a few days old. Labyrinth fish, zebrafish, goldfish, and killifish are particularly susceptible to velvet disease.
Because velvet is highly contagious and usually far too advanced before being diagnosed, it is important to take measures in treating it as soon as possible. Treatment is targeted for the free-swimming stage, tomite, of the parasite.
Copper sulfate is the best treatment. It should be used in accordance with the manufacturer’s instructions for ten full days to ensure that the parasite is completely eradicated. Atabrine, mepacrine, is another medicine that can be used in treating velvet.
Because Oodinium is dependent on light, darkening the lights in the aquarium helps eliminate the infestation. Raising the water temperature to 27°C will accelerate the parasite’s life cycle, making treatment and infestation faster. Adding salt to the water, 1 to 3 teaspoons per liter of water, will increase the production of mucus in the fish to help deter the parasite, and reduce the osmotic stress in the water. Whenever you add any treatment to the aquarium water, the activated charcoal should be removed from the filter, as it will remove the drugs from the water.
Keep the new fish quarantined for two weeks before you put them in the aquarium;
Maintain water quality;
Provide fish with a nutritionally balanced diet.
Velvet usually occurs only when precarious aquarium conditions prevail and is very infectious. Quarantining a new fish for two weeks will considerably reduce the likelihood of contamination of a healthy aquarium. Any fish that appears sick should be removed immediately and stored in a separate aquarium to avoid the spread of the parasite.