Velvet Disease in Aquarium Fish: Spotting the Gold Dust Early

Velvet disease earns its name from the fine, dusty coating it leaves across a fish's body, somewhere between gold and rust in colour, that genuinely does look like the fish has been dipped in velvet powder. It is caused by a group of parasitic dinoflagellates in the genus Oodinium, close relatives of the organism that causes ich, and it can move through a tank just as fast if it goes unnoticed.

Recognising velvet before it spreads

• A fine gold, rust or grey dusting across the skin, most visible when a torch is shone across the fish at an angle in a darkened room
• Fish rubbing or flashing against decorations and substrate
• Rapid or laboured gill movement as the parasite irritates the gills
• Clamped fins, lethargy and a noticeable excess of body slime as the fish tries to protect itself
• Loss of appetite in more advanced cases

The individual parasites are far smaller than the white spots of ich, closer to a tenth of a millimetre, which is why the coating looks like fine dust rather than distinct spots.

Why light matters in both diagnosis and treatment

Oodinium parasites derive part of their energy from photosynthesis, an unusual trait for a parasite and one that gives keepers a genuine treatment tool. Dimming or switching off the aquarium lights for several days weakens the parasite's ability to reproduce and is a standard part of most velvet protocols, alongside medication.

Treating an outbreak

• Turn off the tank lights, or cover the tank to block ambient room light, for five to seven days
• Use a copper based anti parasitic medication, available from most well stocked Indian aquarium shops, following the product's dosing instructions exactly
• Remove activated carbon from the filter before dosing, since it will strip the medication out of the water
• Raising the temperature slightly, to around 28 degrees Celsius if the fish species tolerates it, can speed the parasite's life cycle and shorten the treatment window
• Continue treatment for the full course stated on the product, not just until the visible dusting disappears, since the parasite has stages that are invisible to the naked eye

A caution on copper

Copper based medications are effective against velvet but are also toxic to scaleless fish, shrimp and snails, so any invertebrates or scaleless species such as loaches need to be moved to a separate tank before treatment begins.

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