Freshwater Velvet (Oodinium): symptoms, treatment, prevention

Piscinoodinium pillulare is a photosynthetic dinoflagellate parasite of freshwater fish producing a fine gold or rust dust on skin and gills.

Overview

Freshwater Velvet is caused by Piscinoodinium pillulare, a photosynthetic dinoflagellate. Outbreaks are particularly severe in labyrinth fish (bettas, gouramis) and killifish. Untreated infections progress rapidly and are usually fatal.

Symptoms

Yellow or gold dust appearance on the body
Clamped fins
Scratching against objects
Rapid breathing
Loss of color
Anorexia

Causes

Introduction comes with new fish, contaminated water or plants from infected systems. Stress, poor water quality and bright lighting accelerate parasite reproduction.

Diagnosis

A fine yellow-gold sheen visible at an angle under side lighting, with clamped fins and respiratory distress, suggests velvet. Differentiate from Ich (discrete white spots, not a dust) by appearance and microscopy of a skin scrape.

Treatment

Combine darkness (the parasite is photosynthetic) with a targeted medication. Treat the whole infected tank, since the parasite spreads in the water column.

Quarantine

If sensitive tankmates (shrimp, snails, plants) are present, move affected fish to a hospital tank. Otherwise treat the main tank but remove activated carbon and switch off the lights.

Medication

Blackout: cover the tank completely to block light for 7-10 days; combine with medication.
Acriflavine or a copper-based medication dosed per label for 10-14 days.
Aquarium salt at 1-3 g per litre combined with raising temperature to 28-30 °C for 10 days; less effective than copper but safer for reef-sensitive species.

Recovery

Resume normal lighting gradually after treatment. Conduct generous water changes to remove residual medication, and feed high-quality food to support recovery.

Prevention

Quarantine new fish for at least 4 weeks
Avoid bright lighting during an outbreak
Stable water parameters
Do not skip the cycling stage when setting up a tank