Ichthyophthiriasis Multifiliis

White spot or Ich

White spot or Ich (I. Multifiliis) is one of the most prolific protozoan parasites to be found in aquaculture and the aquatic hobby it is a fact that most hobbyists will encounter, I. Multifiliis, at some point.

It affects all freshwater fishes and lot of salt-water marine fish.

It is the largest protozoan parasite that will be found on koi, the typical white spots found on infected fishes can measure up to 0.5 /1 mm across. White spot are usually thought of and are shown in microscopic photographs as being round with a classic crescent shaped nucleus, whilst in most instances this is the case it is not always presented in this classical manner, the nucleus is usually only seen on the mature individuals, clinically it can and does present itself in an oval shape and minus the nucleus.

Also, I, Multifiliis, in my humble opinion one of the biggest, most rapid and enduring killers of koi there is in the aquatic protozoan world and truly deserves its well-earned respect.

When koi becomes infected mortalities can be both rapid and devastating. Wipe outs of a populous of koi living in a hobbyists pond, does not take long when I. Multifiliis is on the move.

I, Multifiliis, Has one of the most fascinating life cycles, it is important to understand this life cycle, if you are to treat this parasite successfully.

There are four life stages to I. Multifiliis. Although it is another case of which came first the chicken or the egg, we will begin with the parasite living and embedded on the host (the koi) this is called the Trophozoite, or Trophont, at this point in time the Trophont is embedded in between the dermis layers, while it lies here it cannot be destroyed by chemical treatments, without damage to the host, the parasite is quite safe as long as it remains in this state.

*See foot note*

However when conditions become favourable the Trophont will begin to mature and sometime this will be noticed on the koi as the classic white spots over the skin surface as the Trophont moves upwards through the epidermis.

Mention must be made of the fact this will not always be the case, mortalities in koi have been recorded caused by I. Multifiliis without the appearance of the classic white spots, diagnosis has only attributed the disease to white spot after extensive microscopic examination, (so be aware of this fact)

For reference: the classic clinical signs of white spots will appear as if the koi has been very lightly sprinkled with salt, this symptom can be seen with the naked eye as the fish is swimming in the pond with no problem at all, but no detail of the parasite can be seen without microscopic examination.

For detailed observation of I. Multifiliis a microscope of at least x 50 magnifications will be needed

Once the I. Multifiliis Trophont is fully mature to proceed to the next stage it bursts out from between the epidermis layers and up through the cuticle and drops to the pond floor, at this stage in its evolution it can be destroyed, however as soon as it comes in contact with the pond floor or a plant it secretes a gelatinous coat and is soon cocooned, once cocooned, again at this stage it is impregnable to all pond chemicals,

Once the Trophont is encapsulated it starts to finish what it started, by reproducing by multiple fission around 1000 free- swimming ciliate immature larva called Tomites, Theronts or vagrants, these measure about 50 micrometers in size.

As soon as the Tomites are mature enough they will break out and start actively seeking out a host this is the infectious stage, also the main intersection point where chemical treatments are effective and therefore the objective of our chemical treatments.

The Tomite must seek out a host within 48 hours or it will perish and die

In temperatures of 24/26 deg C the whole life cycle takes about 4 to 6 days, it can take as long 40 days in cooler water




If we take in to account the complexities of the life cycle also the invulnerability to chemicals at certain life cycle stages of I. Multifiliis we can easily see that there are only two stages in its life cycle where we can eliminate it from infecting the host and curing the disease,

Those points of influence would be as the Trophozoite free falls to the pond bottom but before it becomes encapsulated and in the free swimming Tomite stage. Realistically we will probably influence the free-swimming stage with chemotherapy more so than the free falling Trophozoite stage, but, itís a case of any port in a storm, with this parasite we will accept any advantage we can gain.

It also follows that because of the complexity of the life cycle and the invulnerability of certain life stages, the use of more than one chemotherapeutic dose (I.E multiple sequenced doses spread over a time period), in any given chemical treatment, in order to eradicate all emerging life stages.


Types Of Treatment

Chloramine T


Malachite Green

Copper Sulphate


Heat, yes, Heat!


Fact, most if not all chemicals tested are unable to penetrate the cuticle (mucus) layer to sufficient depth to attack the embedded Trophozoite, hence the reasoning behind attacking the much more venerable.

It must also be understood that koi heavily infest with white spot to the point where the fish is seriously debilitated and compromised infected host may not survive any and all treatments now matter how successful that treatment may be.

Further to this, in a pond with a heavy white spot infestation and mortalities are being experienced, mortalities will continue for some time after treatment has commenced, for the above reasons, until you get to the right side of this disease,

That said I. Multifiliis, will respond to a number of treatments.


The prime reason for mortalities in koi

Koi or any fishes that are heavily infected with I. Multifiliis that are considered as nearing a terminal condition will appear to be listless and struggling for oxygen uptake, the prime reason for this is, I. Multifiliis destroys gill tissue big time, this is the main cause of death in koi with this disease. Because of this effect It therefore rules some of the more drastic treatments out, that use oxygen from a closed circuit pond system in chemical processes.


Copper sulphate.

Copper sulphate will annihilate I. Multifiliis but it has certain drawbacks. The first being it is no friend of the bacteria in your bio filter and will destroy bacteria in the filter lovingly built up over years, thus water quality problems will surely follow making a bad situation much worst.

Second copper sulphate is toxic to fish in particular koi and this toxicity is dependant on the pH value of the pond water the lower the ph value the more toxic copper becomes.

For these two reasons, copper would not be anywhere near a first line choice of weapon, not even near a last choice against white spot, but as mentioned when your backs against the wall, it may end up being an option, never rule anything out!



It is reported that ramping the heat up into the mid to late 80's will destroy I. Multifiliis whilst this may be true in some cases, there is evidence that one strain/mutation of white spot has evolved to withstand 90 deg and cannot be killed even at this temperature.

As previously stated an infected koi will have some form of gill damage and as warmer water holds less oxygen than colder water this would be an unwise course of action. Additionally even a healthy koi will not do well as these kind of extreme temperatures are reached for the kind of extended time periods needed to eradicate I. Multifiliis.


Chloramine T

The author has personally seen I. Multifiliis withstand multiple dose exposure at four time the recommended dose rate for white spot. Treatments = to 4 gm per 100 imp gallons equivalent to 10ppm, and not even a dent in the disease, although, Chloramine T would go some way to helping with any and all secondary bacterial infections.



I view salt in much the same light as heat. Yes it may work there is no evidence to the contrary. But consider this:because of its universal, world wide every day use in koi ponds, many parasite have adapted over time to continual exposure to salt to the point there is a resistance to salt building in many parasites, salt is no longer effective in many clinical case. This may or may not be the case with white spot and salt, the reason I would personally rather go another route and by pass salt treatments for White Spot is,

Salt will reduce significantly the oxygen content of pond water with its application. It will roughly reduce the saturation point of O2 in water by 1 mg of Oxygen per litre of Water or 1ppm for every, 0.5% Salinity increase.

For white spot eradication a need for at least 0.6% salinity is required coupled with an increase in temperature and as stated in the heat section that heat in itself reduces O2 content, this could be equal to at least a 2 mg/2ppm deficite of oxygen per litre of pond water, dependant on the temperature rise and salinity eventually attained.

Thatís a big oxygen drop, in what will invariably be summer temperatures with an already lower oxygen saturation point, plus a debilitated koi struggling with deficient gill function.

Having said that it is a viable option and for those who prefer a more natural approach, should not be ruled out.


In my Humble Opinion, there is a much more positive route.


Malachite green and Formalin

Malachite green and Formalin despite all the bad press these two chemicals get is the most positive and reliable route to go to eradicate

White Spot. This is achieved with these two chemicals reliably and dependably

Warning! Malachite Green is Carcinogenic and Formalin is particularly nasty to humans also, surgical gloves and safety glasses should be worn for protection, as they should when mixing all chemicals. A pair of glasses is a lot cheaper than an eye!


Malachite green and Formalin used simultaneous or together, <GRIN>in multiple dose will banish white spot in no time at all and is the ultimate weapon against this disease.

Dose at

Malachite green 2%, @ 10 ml per 176 imperial /UK gallons.

Formalin 30%, @ 10 ml per 140/150 imperial / UK gallons


Mix the M/G in a watering can with about a gallon of pond water and apply around the edges of the pond

Mix the Formalin in a watering can with a gallon of pond water and apply around the pond edges, one after the other.

Add extra oxygen to the system in the form of extra air stones to compensate for O2 loss during the early periods of treatment.

Allow to remain in the pond for 5 clear days on the fourth day do a 20% partial water change and a 10% water change on day 5

Then on day six reapply the above dose and protocol.

Leave for a further 5 clear days observing the above partial water changes and re-dose.

The above protocol is for temperatures 20 c and above. Below this temperature allow 7 clear days between applications.

Do not treat below 13 deg c unless really forced too by heavy mortalities.


Your troubles should be behind both you and your koi after this last dose, in fact by about mid term in the treatment you should notice a very noticeable difference and improvement in your fish.


Tests have proved just how difficult it is for chemicals to penetrate the cuticle.

Trials have been conducted that place dyes into the most aggressive chemicals and koi/fishes have been exposed to this treatment.

After treatment the subjects have been euthanasia and frozen. Once frozen the fish have been cross-sectioned and examined under microscope.

Findings to the effect that the even real aggressive chemicals used for white spot treatments only penetrate the very upper layers of the cuticle if at all, leaving the lower regions untouched and therefore the white spot parasite is untouched also. Ref: Dr George Post