External parasites
Freshwater velvet: Piscinoodinium
Freshwater velvet is associated with Piscinoodinium, a dinoflagellate. It is different from marine velvet.
A possible clue
A fine dusty appearance can raise suspicion, but lighting, mucus and normal pigmentation can mislead. Microscopic identification is more useful than judging colour alone.
Use freshwater guidance
Do not copy a marine-fish copper treatment into a koi or fancy-goldfish system. Exact diagnosis, species and water chemistry matter.
When to act
Breathing distress or rapid spread needs prompt professional attention. Keep water readings and the treatment history ready.
Sources & further reading
Original WakeyKoi wording, informed by the references below. Linked clinical resources explain the evidence and their scope; they have not reviewed or endorsed this website.
Related guides
Educational guidance cannot diagnose an individual fish. Breathing distress, severe injury or unexplained losses need prompt professional assessment.