Velvet Disease in Koi

The Dusty Coating That Destroys Skin and Gills

Velvet disease (Oodinium) produces a distinctive dusty, golden-brown sheen on affected koi.

Identifying Velvet

Oodinium parasites — believed to have evolved from algae — attack the skin, gills, and intestinal lining. Infected areas develop a velvety texture, often appearing yellowish to golden-brown in colour. Under magnification, the parasites form grape-like clusters. In advanced cases, skin peels away in patches and fins develop a frayed, split-end appearance.

Impact on Koi Health

Velvet causes haemorrhaging and progressive destruction of the skin barrier. As the protective mucus layer breaks down, fish become vulnerable to secondary bacterial and fungal infections. Gill involvement leads to laboured breathing and, eventually, suffocation.

Seeking Treatment

Velvet shares visual similarities with other parasitic conditions, making microscopic confirmation essential. Do not attempt treatment based on visual assessment alone. A koi health specialist can confirm the diagnosis and prescribe the appropriate course of action.

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Frequently Asked Questions

What does Velvet look like on koi?

It appears as a fine, dusty coating — often gold or brown — giving the skin a velvet-like texture. Fins may look frayed and scales may fall off.

Is Velvet related to algae?

Oodinium is classified as a dinoflagellate and is thought to have evolutionary links to algae, though it functions as a parasite.

Can Velvet be confused with other diseases?

Yes. Without microscopic examination, Velvet can be mistaken for bacterial infections or other parasitic conditions.