Affected fish
All fish.
Cause
Similar to whitespot, Oodinium is a parasite with a life cycle which involves stages on the fish, in the water, and in the substrate. The parasite attaches to the skin, gills, and fins, and causes irritation followed by inflammation and excess mucus production.
Symptoms
Affected fish may exhibit breathing difficulties, flicking, and reddened areas. Large infections produce a light dusting effect and a typical velvet appearance on the fish.
Prevention
Quarantining and good husbandry are the only preventative measures.
Treatment
Formaldehyde treatments are commonly used for velvet disease, and there are a number of proprietary treatments available. The disease has many hiding places and may re-emerge after treatment. Providing good conditions will help prevent further outbreaks.