Marine Velvet (Amyloodinium)

Complete guide to identification, timeline, and treatment

What is Marine Velvet (Amyloodinium)?

Marine Velvet is caused by the dinoflagellate parasite Amyloodinium ocellatum and is one of the most lethal diseases in saltwater aquariums. It appears as an extremely fine gold, rust, or velvety dust on the fish's body — finer than Marine Ich — and attacks the gills rapidly, causing suffocation. It can kill an entire tank within days if not caught early.

Symptoms

Extremely fine gold or rust-coloured dust on body and fins
Rapid or laboured breathing — gills affected early
Flashing or rubbing against surfaces
Clamped fins and lethargy
Loss of appetite
Rapid deterioration — fish can die within 1–3 days of visible symptoms

Causes

Amyloodinium ocellatum — a photosynthetic dinoflagellate parasite
Introduction of infected fish without quarantine
Contaminated water, equipment, or live rock
Stress from transport, temperature swings, or poor water quality
Overcrowding accelerates spread between fish

Marine Velvet Life Cycle and Timeline

Day 1–2
Parasite attaches to gills and skin. Gills are damaged before visible skin symptoms appear. Fish may show breathing changes before any dust is visible.
Day 3–5
Visible gold dust appears on body and fins. Respiratory distress intensifies. Fish flash and clamp fins. Rapid deterioration begins.
Day 6–10
Mature parasites drop off, encyst, and divide into hundreds of dinospores. A single cyst can produce up to 256 new parasites.
Day 11+
Free-swimming dinospores seek new hosts. Without a host they die within 24–48 hours. Leave the display tank fallow for 6–8 weeks minimum.

Treatment Protocol

  • Act immediately — Marine Velvet kills faster than Marine Ich; do not delay
  • Move all fish to a quarantine tank — leave the display tank completely fallow for 6–8 weeks
  • Darken the quarantine tank completely — Amyloodinium is photosynthetic and light deprivation weakens it
  • Treat with copper at therapeutic levels (0.4–0.5 ppm for ionic copper) — use a copper test kit
  • Perform daily 30% water changes to remove free-swimming dinospores
  • Continue copper treatment for a minimum of 4 weeks to break the full life cycle

Medication Options

  • Copper Power or Cupramine (chelated copper) — maintain 0.4–0.5 ppm; most effective treatment for Marine Velvet
  • Chloroquine Phosphate — effective alternative; less harmful to biological filtration than copper
  • Formalin — effective as a bath treatment or in combination with copper for severe cases
  • Freshwater dip (5 minutes, pH/temp matched) — immediate relief; kills surface parasites but not a standalone cure
  • Always use a reliable copper test kit — maintaining accurate therapeutic levels is critical
  • Never treat in a reef tank — copper and formalin are lethal to invertebrates, corals, and live rock
Important

Marine Velvet is one of the deadliest saltwater fish diseases and can wipe out an entire tank in days. Quarantine ALL new fish for 4–6 weeks before adding to a display tank — this is the single most effective prevention. Never add fish directly to a reef tank without quarantine.

Important Disclaimer

The information provided in this guide is for educational purposes only. Always consult with a qualified aquatic veterinarian or fish health specialist before administering any treatments. Proceed with treatments at your own risk. We are not responsible for any adverse outcomes.