Marine Velvet Disease

(Oodinium ocellatum)

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 marine variation is caused by the dinoflagellate parasite Oodinium ocellatum (also known as Amyloodinium ocellatum).

A key difference between the freshwater and marine varieties of the disease is that the marine parasite generally attacks the gills first, meaning that by the time the small gold-like flecks appear on the skin, the infection may be severely advanced. The spots on the skin look similar to that of Ich, but are smaller and a yellow/gold hue.

Damage to the gills can result in the fish losing it’s ability to carry oxygen from the gill membranes to the bloodstream, resulting in suffocation. 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.

The lifecycle of the Oodinium 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. After a time, it detaches and sinks to the bottom to reproduce.

Marine 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


Bibliography & Further Reading

Noga, Edward J. “Fish Disease Diagnosis and Treatment.” 2nd Ed. John Wiley & Sons; 2010

Fenner, Robert. “The Conscientious Marine Aquarist.” TFH Publications; 2001

Stoskopf, Michael K. “Fish Medicine”. W.B. Saunders Co.; 1993

Untergasser, Dieter Ed., “Handbook of Fish Diseases”. TFH Publications; 1989

Duijin, C. Van,. “Diseases of Fish.” Iliffe Books UK; 1973


Noga E.J. (1987) “Propagation in cell culture of the dinoflagellate Amyloodinium , an ectoparasite of marine fishes” Science (Issue 236): p. 1302-1305..

Advisory: The information contained in this article entry is for informational purposes only, and is not a substitute for consultation with a veterinary professional nor treatment under the supervision of a veterinary professional. New Life International does not guarantee the accuracy or completeness of the information nor of the sources cited as reference. This articles is not a diagnostic tool or reference, nor should be considered treatment advice by New Life International.

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