Freshwater Velvet Disease
Common Indicators: Respiratory distress, sluggishness, irritation, gold spots/cysts on skin.
This disease, like many aquarium disorders, has a freshwater and marine variant that share names but are caused by different specific organisms. The freshwater variation is caused by the dinoflagellate parasite Oodinium pillularis.
The lifecycle of this parasite is similar to that of Ich: it starts as a free-swimming dinoflagellate that swims courtesy of a whip-like tail looking for a fish host. Once found, it attaches to the skin and inserts ‘roots’ and forms a hard protective shell that appear as yellow-ish flecks on the skin and look simiar to Ich, but with smaller, gold-like cysts. The organism then will generally spread to the gills, causing damage that can result in the fish losing it’s ability to carry oxygen from the gill membranes to the bloodstream, resulting in suffocation. After a time, it detaches and sinks to the bottom to reproduce.
Common indicators of the disease are the fish staying near the bottom or hanging toward the top of the tank, rapid breathing/ struggling for breath and lethargy, and/or mucus on the gills. Another common indicator is ‘flashing’: fish twisting to rub themselves against surfaces like rocks or coral. An issue with this is that, by the time this symptom is displayed the infection may be extremely severe.
Freshwater Velvet outbreaks can occur when your aquarium population is under stress due to nutritional issues, water quality problems, introduction of new stock (and the associated stress, or possibility that the new specimens are infected), overcrowding or other stressors.