Marine Velvet
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.