Of all Koi parasites, Trichodina is one of the most harmful and needs to be eradicated. The answer lies under the microscope…

If your pond becomes victim to an outbreak of Trichodina your Koi will be irritated, causing them to ‘flash’ against anything in an attempt to remove them, and this, in turn, will cause ulcers. Koi keepers often say “My Koi don’t flash or flick,” but Koi are most active at night when most of the damage is done. In good water conditions, Koi can tolerate low levels of Trichodina, but as soon as a problem occurs, it sparks off an outbreak of parasites. Your fish will produce excess mucus as a defence, but this is the ideal breeding ground for Trichodina.

Tell-tale signs of Trichodina

Fish infested with Trichodina lie on the bottom of the pond, fins clamped, and their white skin looks stressed and pinkish. But these signs are not exclusive to Trichodina and can be indicative of other problems such as water parameters or whitespot. If you suspect Trichodina, always do a microscope scrape to confirm your suspicions. It’s likely that there are a number of other parasites lurking.

Although out of focus, magnified 100x you can determine that this is Trichodina because it looks like a sombrero
At high magnification you can see the cilia move on the outer edge of the Trichodina parasite. An inner ring of claws carry bad bacteria and these cause the irritation

What to look for

Once you have taken a mucus scrape (see Issue 27, Koi health with Dr Peter Burgess), scan around the edges using a magnification rate of 50x. Have pictures available so you know what to look for. Trichodina is almost round in shape with a darker circle in the centre. Its nickname is the ‘Mexican hat’ because it resembles one under a microscope.

Trichodina can be confused with simple air bubbles, but by adjusting the fine focus you can see an air bubble is perfectly round. Trichodina becomes obvious with magnification of around 150x – you can see cilia moving on the edges of the parasite. If your pond water is warm Trichodina is more active on the slide and it shows up clearly under the microscope. Being one of the larger parasites it is normally a good starter when identifying parasites for the first time. and the subsequent fry.

Treating Trichodina

Frogs and toads carry Trichodina but are no risk to your Koi. Trichodina is commonly present in ponds, but outbreaks only occur if Koi are stressed or unhealthy. The treatment for Trichodina is potassium permanganate at a rate of 1.5g per 220 gallons. Remember to switch off UV units when treating, and don’t use when the water is salty. This treatment can have a harmful effect on your pond filters and will deteriorate a Koi’s skin quality.

If your pond is new, the filter should be turned off or bypassed to avoid wiping out beneficial bacteria. In either case, lots of oxygen should be added via air pumps. Treatment can be administered at low water temperatures, but no lower than 10°C.

1 Mix the levelled amount with hot water, stir thoroughly and then let the solution stand for 30 minutes adding an airstone to gas off any toxins.

2 Add slowly, keeping a close eye on your Koi.

3 Repeat this treatment according to temperature.

4 Do not overdose, always read the dose rate required and avoid using potassium permanganate if it has been in the cupboard for over a year.

Get results

It is always a good idea not to feed 24 hours before treatment is administered, and it’s essential to monitor water parameters afterwards. This treatment is only active for up to eight hours, depending on how much blanket weed and silt there is in your pond.

After several hours the water will turn a brown, scummy colour, meaning the treatment has worked. You may need to do a water change of 10 per cent, but it’s not always necessary. Check levels of ammonia and nitrite after each dose to monitor the filter bacteria’s performance. The worst thing is overfeeding your Koi at this point because food adds more waste and more ammonia, and this means more stress and further outbreaks of parasites.

Top Tips

> Identify which parasite is causing the problem before treatment.
> Turn off the UV unit when treating your pond.
> Follow the label’s instructions and do not overdose. Chemicals can cause serious damage to your Koi if they are abused or if amounts are miscalculated.
> Make sure the pond water is salt-free because it can harm Koi when used with most chemicals.
> Keep good water conditions and the resident parasites will be kept to a minimum.

Cilia Are tiny hairs along the outside of the parasite membrane wall, which aid movement.