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Parasitic

Marine Velvet

Amyloodinium ocellatum
Also called: Coral fish disease, Saltwater velvet
CriticalSaltwaterContagious
Not veterinary advice. Symptoms overlap between conditions and a wrong treatment can make things worse. Consult an aquatic vet for valuable specimens or anything not responding to standard treatment.
Adult Siamese fighting fish (Betta splendens) with a heavy dinoflagellate velvet infestation — the dusty gold-brown sheen across the body and fins is the same signature appearance produced by the marine equivalent (Amyloodinium ocellatum). Marine velvet is best spotted under a flashlight in a dim tank.
Adult Siamese fighting fish (Betta splendens) with a heavy dinoflagellate velvet infestation — the dusty gold-brown sheen across the body and fins is the same signature appearance produced by the marine equivalent (Amyloodinium ocellatum). Marine velvet is best spotted under a flashlight in a dim tank.
Mydigitalife. (2011). Betta splendens with severe Oodinium velvet infestation [Photograph]. Wikimedia Commons. Public domain.

Symptoms

Fine gold or dusty sheen across the body, like the fish has been sprinkled with powdered sugar. Often easier to see under a flashlight in a dim tank. Rapid gilling, scratching, color loss. Velvet kills FAST, fish can die within 24-48 hours of symptoms appearing, often before the gold dust is widely visible. Sudden mass mortality without obvious cause is often Velvet, especially in clownfish.

Causes

A dinoflagellate parasite, closely related to the algae that bloom red tides. Lifecycle: trophont feeds on fish (especially gills), drops off, divides into hundreds of dinospores per cyst, dinospores infect new hosts. The gill phase is what kills, fish suffocate. Highly contagious. Tangs and clownfish are extremely susceptible.

Treatment

Copper sulfate at 2.0 ppm therapeutic level in a hospital tank, same protocol as Marine Ich, treat 30 days minimum. Chloroquine phosphate works faster and is preferred for active outbreaks. Move surviving fish to QT IMMEDIATELY at first symptom, every hour matters. Freshwater dips (5 minutes in dechlorinated, pH-matched, temperature-matched freshwater) provide emergency relief but are not a cure. Display tank must go fallow 76+ days.

Prevention

Quarantine every new fish, including 'reef-safe' species. Watch newly-introduced fish carefully for 2 weeks. Velvet often hits within days of stress. Don't skip QT for 'one quick fish.' Tang-heavy reef stockers should treat QT as non-negotiable.

Notes

Velvet is far more lethal than Marine Ich. A reef with Velvet can lose every fish in 72 hours. If you suspect Velvet, treat as an emergency, copper or chloroquine within hours, not days.