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parasite like

Velvet (Oodinium / Amyloodinium)

Fine gold, rust, or yellowish dust-like shimmer on the body and fins, often with intense flashing and rapid breathing. Caused by the dinoflagellate parasite Oodinium (freshwater) or Amyloodinium (marine). Often missed until advanced because the coating is subtle.

Urgentpattern match not diagnosis1 source note

Do first

  • Dim or turn off aquarium lights immediately Oodinium requires light for its free-swimming stage.
  • Test water quality and correct any issues.
  • Do not add new fish.
  • Remove activated carbon before treating.
  • Treat all fish in the tank, not just affected individuals velvet spreads very rapidly.

Escalate if

  • Any fish gasping, listing, or showing severe breathing difficulty gill involvement is life-threatening.
  • Multiple fish dying rapidly (velvet can kill an entire tank in 24–48 hours in severe outbreaks).
  • No visible improvement after 5 days of correct treatment.

Water clues

These readings can push this pattern higher or lower in the triage result.

ammonia above zero+3

Poor water quality increases susceptibility to velvet correct water quality before or alongside treatment.

nitrite above zero+3

Nitrite stress combined with velvet is often rapidly fatal.

Care protocol

Follow only the steps that fit your species, tank inhabitants, and medication label.

Confirming velvet

  1. Use a torch or penlight held at a low angle across the fish's body in a darkened room.
  2. Look for a fine gold, yellow, or rust-colored dust velvet has a slightly metallic shimmer, unlike ich's white salt grains.
  3. Check the fins first the shimmer is often most visible on thin fin tissue.
  4. Affected fish often 'shimmy' or shake as if trying to dislodge the coating.
Cautions
  • Velvet can be confused with ich at a glance the color and texture differ significantly under close inspection.
  • Do not delay treatment for extensive confirmation; velvet progresses very quickly.

Freshwater velvet treatment

  1. Darken the tank immediately (cover sides and top) to inhibit the dinoflagellate's photosynthesis.
  2. Treat with a copper-based medication or formalin-based treatment appropriate for your fish species.
  3. Raise temperature gradually to the upper range of all species' tolerance (if safe) to speed the parasite life cycle.
  4. Increase aeration to compensate for warmer water.
  5. Maintain treatment for a minimum of 14–21 days.
  6. Vacuum substrate regularly to remove tomonts.
Cautions
  • Copper is toxic to invertebrates, snails, and many plants. Use a hospital tank if these are present.
  • Scaleless fish require halved doses of most treatments.
  • Do not use salt as a primary velvet treatment. It is largely ineffective against Oodinium.
  • Never combine multiple medications without verified compatibility.

Source notes

References and context notes used for this triage entry.

Oodinium (Velvet Disease) MERCK Veterinary ManualVeterinary reference conservative and evidence-based.
Run Symptom CheckerCompare this pattern against water readings, affected count, and recent tank context.Ask AdvisorUse TankFlare Advisor to review this against your saved tank and recent logs.

Related patterns

Similar symptoms or risk factors worth comparing before treatment.

UrgentMarine velvet (Amyloodinium ocellatum)

The marine equivalent of freshwater velvet an extremely fast-moving dinoflagellate parasite causing gold or rust-colored dust on marine fish, rapid breathing, and quick death. Amyloodinium is considered one of the most dangerous diseases in the marine aquarium hobby and can kill an entire reef tank's fish population within 2–3 days if untreated.

High priorityGill flukes or body flukes (Dactylogyrus / Gyrodactylus)

Rapid breathing, gill flaring, flashing, and scratching caused by microscopic monogenean parasites on the gills (Dactylogyrus) or skin/fins (Gyrodactylus). Often introduced with new fish. Requires microscopic confirmation for certainty but may be treated empirically when symptoms are consistent.

UrgentBrooklynella hostilis (clownfish disease)

A rapidly progressing skin ciliate that preferentially attacks clownfish (Amphiprion spp.) but can infect other marine fish. Causes excessive mucus, sloughing skin, rapid breathing, and fast deterioration. Often fatal within 24–48 hours without treatment. Can be confused with marine velvet but has a distinct slimy, sloughing appearance.

High priorityMarine ich (Cryptocaryon irritans white spot disease)

The marine equivalent of freshwater ich white salt-grain spots on skin and fins, with flashing and rapid breathing. Caused by the ciliate Cryptocaryon irritans. Nearly ubiquitous in marine aquariums and one of the most common diseases in reef tanks. The display tank must go fallow while fish are treated in a hospital tank, because Cryptocaryon cannot be treated safely in the presence of corals and invertebrates.