Velvet disease (oodinium) in aquarium fish — symptoms, treatment, prognosis
Golden-grey 'dusty' coating on the skin, fast breathing, loss of appetite. A dangerous dinoflagellate parasite — treated with darkness, copper and heat. Without therapy, mortality in 3–7 days.
Velvet (oodinium) is caused by the parasitic dinoflagellate Piscinoodinium pillulare. Unlike ich, the parasite is smaller (50–80 µm) and produces not discrete spots but a solid dust-like film of a golden-grey shade, especially visible under side lighting.
Symptoms: gold-dust coating on flanks and gills, fast jerky breathing (the parasite attacks the gill epithelium first), flashing, clamped fins, lethargy, refusal to eat. Labyrinth fish (bettas, gouramis) and small tetras are often the first to fall. Velvet progresses faster than ich.
Treatment and prognosis
Protocol: black out the tank with a heavy cloth for 7 days (the parasite photosynthesises and weakens without light), raise temperature to 28 °C, dose a copper-based medication (copper sulfate at 0.15 mg/L Cu²⁺ or a commercial product such as Esha Oodinex or Sera Oodinopur) per label. Remove activated carbon. Salt 1–3 g/L as an adjunct (NOT for tetras or corydoras).
Prognosis: with early treatment, 70–80% of fish survive. Prevention — 3–4 weeks of quarantine for new arrivals and stable water quality. Stress and abrupt temperature changes are the main triggers of an outbreak.
FAQ
- How does velvet differ from ich?
- Parasite size and coating pattern. Ich — discrete white spots 0.5–1 mm; velvet — a fine golden 'dust', as if dusted with pollen. Velvet is more aggressive and hits the gills first.
- Can I dose copper in a main tank with plants and shrimp?
- No. Copper is toxic to plants and lethal to shrimp and snails. Treat in a separate hospital tank without live plants or invertebrates.
- How soon after symptoms appear should I treat?
- Immediately. Velvet moves faster than ich — a day's delay halves the fish's chances.
Scientific board — ichthyologists and veterinarians
Ichthyologists and veterinarians with university degrees · Reference FishBase, Seriously Fish and peer-reviewed literature · Sign every reviewed article with their credentials shown
Aquascaper, IAPLC top-ranked finalist, specialist in Southeast Asian biotopes
Top-ranked IAPLC finalist (International Aquatic Plants Layout Contest) · 20+ years designing freshwater aquariums · Member of the Aquascaping Society of Japan
Sources
- Seriously Fish — Velvet (Oodinium) · Seriously Fish · 2026-05-31
- Practical Fishkeeping — Velvet disease guide · Practical Fishkeeping · 2026-05-31