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Case studies

Crouching Tiger


Over the years I have had many puzzling experiences with Koi. The first thing that comes to mind is the six Koi that survived under horrific circumstances for months when a house was on sale. There were no pumps running and no maintenance. It took the new owner weeks to give attention to the neglected pond. After removing a few plastic chairs, old bird cage etc, he saw movement! Today the six Koi are still in the now well maintained pond and doing well.

Then the question springs to mind: Why don’t a dedicated Koi keeper like a friend of mine in Richards Bay have the same luck with a pristine pond of 50 000 litres? In this instance it took us two weeks of agony and still we could not save his precious collection of Koi. A silent stalker was lurking but we could not identify it! This big pond is equipped with four bottom drains, a settlement chamber, large filter and UV. The turnover rate is at least once every 90 minutes. In the last filter chamber was a platform, supporting various plants, but mainly water iris.  Water is returned to the pond via two aim flows and a small water-curtain, 35 cm wide and about 40 cm high.

On the property is also a quarantine pond, fully equipped.

How it all started....


It all started during the middle of summer 2009 when the four Kohaku in the pond showed signs of stress. The symptoms were tell-tale red stress related veins on the white skin. We went through the whole process of taking readings of the temperature, pH, hardness, ammonia, nitrite and nitrate. All the readings were within normal parameters. Mucus scrapes were taken to determine if there were any parasites. None were found. What we did not test was dissolved oxygen and heavy metals.

As we could not find any apparent reason for the stress, I wrote to Lawrence Belshaw in the UK who suggested (from the little information that I could give him) that it could be a low level of Costia infection. Still we could not find any parasites.

Then came spring, a time dreaded by many Koi lovers. The owner executed two Potassium Permanganate treatments a few days apart as a precaution against the proliferation of parasites during this time of unstable temperatures. Within a week of the last treatment, one of the fish, a favourite Midorigoi, started to sulk at the bottom of the pond with spread pectoral fins and normal gill movement. Again we went through the whole process of testing the water parameters and scrapes. Nothing was found. At this stage we became worried.

Two days later the Midorigoi and an exceptional Kohaku developed smallish white lumps of slime on the head and dorsal area and the Midorigoi further developed dark blotches all over the skin. It really resembled something prehistoric. The gills were by now dark red and there was rapid gill movement. Although it was classic parasite infection symptoms, we could not find parasites! We sat for over an hour discussing the symptoms, filter system, water quality, absence of parasites and the way forward.


We removed the Midorigoi  to a quarantine pond, did a 15% water change and added salt to both the quarantine and the main pond (0.3 %),  because we believe Chilodonella and Costia may be the culprit (without proof!) and the salt will also de-stress the fish. I also injected the Midorigoi with Baytril. Next day the situation seemed to stabilize. After the second day, it became evident that the situation was worsening.  At least six fish were displaying the same symptoms of either slime, skin darkening or dark red gills. All of them were injected with Baytril and then we realized we were in a fix. The salt did not have the therapeutic effect as hoped and we could not ad Formalin and Malachite Green to the pond which already contained 0.3% salt. For the same reason we could not treat with Potassium Permanganate. The gills were in such a state that we were afraid that any one of the above treatments may kill the collection. The idea of KHV was always at the back of our minds, but no –one was willing to even discuss the possibility.  The situation was getting out of hand. We sat with good water, sick fish and no evidence of parasites. Bacterial infections were a real threat by now and we continued with injections and added Acriflavine to the pond. The Midorigoi was showing some improvement by now and we started to get more optimistic.

Two days later the first fish died. I took the risk of taking a mucus scrape on the inside of the gill plate of a severely affected fish. Although I spent literally hours behind the microscope, I could find no parasites.

By now I was desperate. Nine fish have died and a prized Jumbo Chagoi became sick. While injecting it (this time with Nuflor) I could feel the dorsal area was already “spongy”.  A very bad sign under any circumstances. We added six air-stones to the pond and proceed to do a massive water change.  I then noticed a small Kujaku lying at the bottom of the pond. The gills very barely moving and it was clear that for all practical purposes the fish was dead. I took a very invasive gill scrape drawing blood and mucus and proceed to examine it under the microscope without much enthusiasm. I almost fell off the chair. Countless organisms were gliding around in the mucus sample! It was not an organism that I have previously encountered, but at least there were now some evidence on what we were dealing with. When the water change was done, I added Formalin and Malachite Green and rushed home to try and determine what we were dealing with. The risk that more fish would die from a Malachite Green and Formalin treatment was not an issue any more, because the fish were dying anyway.

Calling for help

The first reference was all the books that describe Koi parasites but I could not find anything resembling the problem that we faced. The next reference was Duncan Griffith’s web-site, www.koiquest.co.uk.  The first video that I clicked on gave me the answer! Tetrahymena. I phoned Chris Neaves and also sent him a description of the parasite and symptoms. He immediately took an interest and forwarded the e-mail to Duncan Griffiths and Spike Cover. The responses were not very encouraging, but it seemed that Malachite Green and Formalin was the correct way to go.


During all this, we foolhardily refused to give in and test for KHV and continued with the quest to find some answers. The trouble was that I am not equipped to identify the specific species of Tetrahymena spp. Most authorities however agreed that T Corlissi and T Pyriformis are the dominant species. Here is a summary of the information that I could gather.

Fish disease Diagnosis and Treatment, Edward J Noga:

Tettrahymenids are typically free living ciliates, but some species can be highly lethal fish pathogens, notably subspecies Corlissi and Pyriformis. The species most commonly causing disease is Corlissi and in advanced stages can invade various internal organs like muscle, kidney, brain etc. Reproduction is by binary fission but can also produce small reproductive cysts (2 to 8 tomites)

Tetrahymena may be confused with free-living, non-pathogenic ciliates, such as Parameccium, which may occasionally be found in low numbers on the skin and gills. However the shape, size and movement could be used to differentiate between them. Penetration of muscle and deep tissues is one way to diagnose Tetrahymena. Only cases that have not become systemic are treatable. The recommended treatment by Noga is a formalin bath.

The Merck Veterinary Manual -Protozoa Infecting Gills and Skin

Tetrahymena Corlissi, another ciliate, may be motile and surface-dwelling but is also occasionally found within tissue, including skeletal muscle and ocular fluids. Tetrahymena spp are pear-shaped and 10-20 µm long, with longitudinal rows of cilia and inconspicuous cytostomes. External infestations of Tetrahymena spp are not uncommon on moribund fish removed from the bottom of a tank or aquarium and are often associated with an environment rich in organic material. As long as Tetrahymena spp are restricted to the external surface of the fish, they are easily eliminated with chemical treatment and sanitation. When they become established internally, they are not treatable and can cause significant mortality. Fish with intraocular infections of Tetrahymena spp develop extreme exophthalmoses. The parasite is readily identified by examining ocular fluids with a light microscope.

Fancy Guppies

The most disturbing information that I found is published on
www.fancyguppies.co.uk. The article, Guppy Disease……… One to Avoid! by David Rodgers, is very informative and to an extent very disturbing. It describes the parasite in detail as well as the way it reacts on a host. David kindly gave his permission that I could use the information to assist fellow Koi Keepers. It would be an injustice to the article to quote only certain aspects. The full article is therefore quoted here. It is further worth mentioning that David suggested during our correspondence, that the best treatment against this parasite is a salt dip.

Brett Edgerton.

“Once within host tissues, the ciliates were actively histophagous but the actual mechanisms used to break apart host cells are not known. It has been suggested
that ciliary action and extracellular lysosomes provide both mechanical and chemical means for disrupting tissues and cells (Armstrong et al. 1981). All systemic ciliates detected in crustaceans possess small subapical mouthparts and their oral cilia are used to sweep small fragments to the cytostome rather than to actively break apart cells. The role of the somatic ciliature in feeding processes is not known but many ciliates appeared to repeatedly probe clumps of cells with their anterior cilia. Further studies are required to determine the mechanisms by which histophagous ciliates disrupt host tissues and destroy cells.”

Continued treatments and setbacks

Armed with more knowledge and the fact that the Malachite Green and Formalin that was added to the pond should do the trick, it was normal to fall into a false sense of security. The second day after the treatment with Malachite Green and Formalin my friend called to say that another six fish have died. By now it was not possible to keep count of the fatalities. We were all devastated. The pond was in a sorry state. As expected, the fish with the most damage to the gills did not survive the Formalin treatment, but the rest of the collection seemed worse! As I arrived, another fish that has showed no symptoms gave a few quick darts through the water and died. We removed the fish and placed some of its gill filament under the microscope. The gills were dark red with no dead tissue. The number of the same parasites identified a few days ago moving around was staggering. Obviously the Malachite Green and Formalin had no effect on the numbers.

We also had no choice but to euthanize the prized Chagoi and family pet. I could still find no parasites on the skin!  The problem was definitely on the gills and systemic.



The day after euthanizing the Chagoi, Saturday 3 October 2009, a mucus sample taken from the gills was posted to Molecular Diagnostic Services for a KHV test. I also received more e-mail from Chris Neaves, Duncan Griffiths and Spike cover. They must be getting fed-up with me by now. These gentlemen were extremely helpful. The following suggestions were made.

Spike Cover:

“If it's been 2 days after the first F/MG Tx and the parasites are still at high numbers, something is wrong.  Here are several possibilities:

1. The diagnosis is wrong, so
2. The Treatment is wrong, or
3. The med dosage is wrong, or
4. The water is so polluted that it's using up the med before it has a chance to work.

Here's how to try to sort it out:

1. Confirm the diagnosis, you can take a picture thru the scope if you just stick your digital camera up to the eyepiece and move it back and forth until you get focused.  If we actually saw this bug, we (Dunc and/or I) might be able to help with the diagnosis.
2. Make sure all the meds are current (not out of date or degraded, say by heat), and
3. Make sure the meds are being dosed at the correct rate - this means knowing what the water volume is within a reasonable amount (to estimate the formalin dose to see if you're in right area, Pieter should be using about 100 ml of formalin per 1000 US gallons to achieve 25 ppm - it's actually about 95 ml but it's easier to remember 100) and
4. If the system has lots of crud in it, clean it all thoroughly, do a potassium permanganate treatment (2 ppm) to knock down the DOCs in the water before the next F/MG treatment.  Keep redoing the PP treatment until the water stays pink for at least an hour, and then start the correct treatment again.”

Duncan Griffiths

“This (Tetrahymena) is not in parasite terms a huge predator/harvester of Koi usually if this is found on dead or dying fish something else is usually the root cause. This has just jumped on because there is an abundance of natural food because the fish is no longer clean.

This parasite is not really a parasite. The Koi has nothing directly it wants.  The Koi supplies the environment at times that make the food it feeds upon flourish and bloom, Tetrahymena has nothing on its person even to do any damage to a Koi

Now funny enough, the last time I saw loads of these was on fish that were checking out with KHV the one on the movie zone I’m pretty sure came off a KHV fish.

Now we get to the interesting bit and I hate to be the harbinger of doom, from the way the symptoms are being described and the excess mucus sloughing, temperature and the speed of deaths. Over a period of 4 days, 9 fish died, this could well be KHV you would be a mug to bet against it.”  

So I would go down the KHV route while also checking fresh faeces. Squash samples under the scope for Hexamita.”

The correspondence from Duncan has put an end to the speculation about this mysterious parasite. KHV was not only at the back of our mind. Someone has now brought it into the open and we took the swabs and dispatched it to MDS in Pinetown. So, with the KHV test posted, the only things outstanding were the test for Hexamita and continued treatment. The Faeces test did not show any Hexamita. What I knew was that the water did not contain too much organics and that this impression may have been created by the Eugenol in the water while putting the Chagoi to sleep. Upon checking on the Midorigoi in the quarantine pond, it was heartening to notice that she has recovered to such an extent that she is starting to feed now. We injected the Midorigoi with Baytril once a day for three consecutive days and on the fifth day, Nuflor intra peritoneal. 


My own note at this stage. It seems that the infected fish may not survive this outbreak of whatever is killing the collection. Maybe it is KHV, I cannot be sure. Fish that actually showed no symptoms and were eating well, died.

Wednesday 7 October 2009. The worst day for the owner and myself in all our time of keeping Koi. The results of the KHV tests came back. Positive. It is not possible to describe the emotions that went through all of us.

First of all, a decision about the future of the fish in the infected pond should be made. After partially recovering from the shock, the owner made his decision to euthanize the rest of the collection.

Secondly, we had to try and figure out how it happened. It was complicated. I wrote to the three wise men:

“The results of the problem pond came back. It is KHV positive. The owner has opted to euthanize all the remaining fish. ..

It is a sad day.

Now we must try to trace the origin.”

This last sentence created a new debate:

Chris Neaves

I am sorry to hear this.
Yes try to trace where the fish came from. It’s a bugger when it happens. It is also a good thing that you found out what is going on. Which proves our original point – don’t guess – test.

Can you finish your letter to KOISA on the matter and how you discovered it, the support you gave to the guys in your area etc. What you sent me is already looking good. Then I think you must place it on your website. There is really good info there. If I can be of assistance again please don’t hesitate to ask. And please mention to the owner of the pond this type of thing has happened to all of us and me included. Also there is no such thing as a retreat you are merely advancing in another direction.

Duncan Griffiths

What makes Pieter think he can identify the carrier of this disease? It could have been in this pond 5 minutes, it could have been there 10 years.

Duncan Griffiths

I'm going to try and save you all some grief, time and trouble herein trying to find the culprit.  Feel free to jump in Spike, if I'm off target here. It’s a complete waste of time and effort trying now to find where the carrier came from for various reasons not least of which because: 

It only takes one carrier to start a KHV outbreak but that one carrier need not have been the only KHV carrier in the pond. There could be multiple carriers introduced at various points in time.

The carriers could have been in the pond for years or it could have been in the pond for five minutes. You have no way of determining this. People have an auto response (understandably but wrongly in my view) a lot of the time, to blame the last Koi in the pond and therefore that supplier) 

Last but not least, the carrier or CARRIERS,  had the disease played out  completely  and naturally  would have likely been amongst the survivors when the disease had run its course,  when the decision was taken to  employ euthanasia  for the entire population  this opportunity was lost forever. 

So at this point it’s futile to try. It will spread ill feeling and suspicion with no decent evidence.

If you really want to find out chapter and verse and even this would not be 100%,  this has to be done before any KHV outbreak  and would involves Elisa testing the whole  population  for KHV antibodies provided none have been vaccinated against KHV. When the results come back this will show the positive KHV subjects that have been exposed to the disease and therefore the breeder, if known, and the dealer who supplied the fish.

Publishing these events

Folks can be cruel and the guy in question will be ridiculed, no matter if he is named or not he will know who the ridicule is aimed at and will feel this. The irony is the critique will come from people that can talk the talk but will not walk the walk themselves. 

Let me explain this.

Over the last 10 years there has been enough stuff written on KHV to sink a decent sized battleship yet here we are 10 years on and the disease has got massive spread worldwide. Yet folks get KHV in their ponds ever day of the week, whereas 10 years ago it was a rarity

This tells me, after all we have learned and wrote about this, we actually have learned nothing and the reason is basic, the whole world and his dog know what we need to do about this. We need to buy for  dealers that ideally  conduct Elisa testing  on **ALL** their stock, or at the very least buy from a dealer  that does a serious proven heat ramping regime Last but not least,  instead of wasting time looking for the breeder /dealer remember the fact that  quarantining  and screening is the  buyers responsibility  as well. Even if the dealer is a good dealer that does some of the above, this is not an excuse for avoiding quarantine at home.

So why does this stuff keep rearing its head?   Because despite the horror stories on web sites /forums/ magazines, and all the data contained therein folks think KHV happens to other folks. It can never happen to them, quarantine is stuff other folks do but they are immune from having to use it. Heat-ramping your stock is well documented worldwide but folks think it’s not applicable to them. Why go figure? I guess this is just human nature, not lack of knowledge.

There is no point in Spike, the media or myself, describing a crouching tiger, if folks think that despite being in the immediate vicinity, this poses no threat and is low risk. As we know it only takes one carrier.

Hobbyists and dealers the world over  know all this right now they know the risks, but choose to ignore it and that's all it takes for this disease to survive and is ultimately the secret  of its success.

Spike cover

I don't have time for an exhaustive explanation but here are some facts that reinforce what Duncan has said.

Earlier this year, I shipped 10 Koi to Oregon State Univ. to a DVM, PhD there who specializes in herpes virus.  These fish had been in quarantine at a dealership in So. Cal. for about a year with no signs of KHV.  Those Koi had come from a breeder/dealer in Japan who, a year prior, had supplied Koi to a dealer in Texas.  Several of those Texas fish broke with KHV soon after their sale (no quarantine at the dealer).  When the So Cal dealer heard of the outbreak, he held the fish from the same breeder/dealer and refused to sell them (good for him).

The PhD at OSU killed those fish and was able to get KHV to grow in tissue culture from samples taken from 8 of the 10 Koi I sent her.  Remember this was AFTER a year with no signs of KHV in the group (I estimate that there were about 50 or more fish being held in that batch by the So Cal dealer).  BTW, to my knowledge, getting the disease into tissue culture from fish that long w/o clinical signs of the disease had never been reported in the world before this.  These folks are now involved in an $80,000 grant program to study the method of persistence of KHV in Koi.

Note: the So Cal dealership early on (soon after the reported Texas outbreak) sent blood samples to Univ. of Georgia for serology testing for KHV antibodies.  Some samples were positive.  Later, additional samples sent to UGA were negative.  However, samples sent to the Univ. of California at Davis tested positive for KHV antibodies at the same later dates.  (Different tests performed at the two different labs).

Sophie St-Hilarie et al have published two papers indicating that Koi can and do form carriers that can break with the disease after their survival from an initial occurrence of the disease.  Whether the disease is latent or a low level persistent infection was not determined.  The most recent article (2009) states that, in their testing, 10% to 25% of the KHV survivors develop high antibody titers (1/1600 or greater by their test methodology).

The "So what?" is that carriers for KHV exist in Koi.  And those surviving carriers can infect others months after an initial outbreak.”


Duncan Griffiths

“Thanks Spike, that was great. You went to lengths that quite honestly I could not be bothered with, 10 years of data is enough for me, and my attitude is shoot it or salute it the choice is yours. 

Trust me,  you are wasting your time trying to point a finger that this juncture, I know full well you want to name names , but this action could land you in more trouble than it’s worth given that all your evidence is probably under a rose bush by now

If you still feel like you want to pursue this, knock yourself out”

Chris Neaves

“Spike, I am using the KHV summary you sent me for inclusion in our Health Guide/Manual re-write. I would also like to include what was basically said about the virus in this series of emails. It illustrates the problems confronting Koi keepers and Koi dealers when trying to identify the source of KHV out breaks. It is also sobering information for Koi keepers who are very quick to point fingers and tends to pull the trigger far too easily”.

This whole episode was traumatic for the owner as well as me. For me personally because of the total feeling of inadequacy in not being able to help and to watch helplessly while a collection of Koi succumb. For the owner obviously more traumatic for these were all Koi that was raised by him and were more than just pets.

I am sad to report that subsequent to the events described, the pond was filled up and paved over. The owner did not want to go through such an experience again. He was afraid to start a collection again because he feels there is no way to guarantee that this will not occur again. Especially in the light of the fact that even carriers may not be identified during the KHV tests and may well infect a new collection. Whether one agrees with these sentiments or not, it remains a personal decision.


Well Spike Cover put it very eloquently: Experience is something you don't get until just AFTER you needed it.

From what I have learned during these last few weeks, I have added the following to my web-site:

Can we ever win the battle?

I have experienced an outbreak of this terrible virus only once. Rest assure, nothing can prepare you for the real life experience of a KHV outbreak. What you learn in all the studies and descriptions about the symptoms associated with KHV can at most, only be regarded as very general indications that the virus is present. Not all Koi will exhibit the same symptoms. The symptoms were the following:

The first fish, a Midorigoi that showed symptoms, became lethargic/fatigued and stayed on the bottom of the pond with fins spread. There was no rapid gill movement.  One circular black dot, one centimetre in diameter appeared below the lateral line.

Next day, the Midorigoi remained at the bottom of the pond and developed black blotches all over the body, with smallish white clumps of slime on the head and dorsal area. The fish resembled something prehistoric. Also on the second day, more fish became lethargic on the bottom of the pond. No parasites were found on any fish. Salt and Acriflavine were added to the pond.

In the course of the next week, more than half the collection started to show a variety of symptoms, while some fish died without showing any abnormal behaviour. The symptoms showed were the following:

Heavy mucus excretion
Rapid gill movement
Spiral swimming
Fish will stay at surface of the pond with dorsal fin and upper part of the tail fin above the water.
Lying at the bottom together in groups
Mad dashes around the pond
No symptoms at all
No symptoms and still dying
In the latter stage of the infection, fish will weakly lie on their sides with gills barely moving and the occasional tail movement
Redness of the whole body, gill plates and fins
Deep red gill filament
Bleeding from the gills
Blood oozing out from under the scales
No visible ulcers
Accumulation in the scale pockets
Dry patches where scales have died and feel like sand paper
Sunken eyes
No fin erosion
Internal bleeding
Yellow mucus-like fluid in intestines, running from mouth when fish is lifted out of water
Tetrahymena found amongst gills of almost every weak fish lying on the bottom of the pond
I have not seen the notch on the nose or grey streaks of gill necrosis in any of the cases. The only common symptom that I have witnessed in deceased Koi is that the gills were severely damaged, dark red and covered with a jelly-like mixture of dark red blood and mucus.

I would like to repeat, not all the symptoms will be present in a pond infected with KHV. In fact only a few symptoms may be visible and the symptoms may for a time be very subtle, often resembling a normal parasite infection. Only very resilient Koi will develop ulcers. The infected fish die so quickly that there is hardly time for ulcers to develop.

Regardless of the symptoms, if tests show acceptable water parameters and fish do not respond to conventional parasitic and bacterial treatments, test immediately for KHV.

One can just read the two KHV articles in Koiquest and Fish Helpline to realize that KHV is here to stay. Links to both these web-sites can be found under Web-sites worthwhile to visit. With the recent (2009) outbreaks of KHV in South Africa, every Koi keeper and dealer will have to undergo a paradigm shift regarding quarantine, to protect themselves and others from this terrible disease. 

There is a big debate and finger-pointing in the October 2009 edition of KOISA about who should accept responsibility for the recent outbreak of KHV in South Africa. I would like to quote a few paragraphs from a recent international debate and information sharing between heavyweights Chris Neaves, Duncan Griffiths and Spike cover, that I had the privilege to witness. The debate centred on KHV and later on addresses the consequences of going public and attempting to trace the source. In conclusion I would like to quote some selected paragraphs received from the well-respected Duncan Griffiths during the debate in this regard: 

“It’s a complete waste of time and effort trying now to find where the carrier came from for various reasons not least of which because:

It only takes one carrier to start a KHV outbreak but that one carrier need not have been the only KHV carrier in the pond, there could be multiple carriers introduced at various points in time.

The carriers could have been in the pond for years. It could have been in the pond  for five minutes. You have no way of determining this. People have an auto response (understandably but wrongly in my view) a lot of the time to blame the last Koi in the pond and therefore that supplier)

So at this point it’s futile to try. It will spread ill feeling and suspicion  with no decent evidence.
If you really want to find out chapter and verse  and even this would not be 100%,  this  has to be done before any KHV outbreak  and would involves Elisa testing the whole  population  for KHV antibodies provided none have been vaccinated against KHV. , when the results come back this will show the positive  KHV subjects  that have been exposed  to the disease  and therefore the breeder if known and the dealer who supplied

.., last but not least,  instead of wasting time looking for the breeder / dealer, remember the fact that  quarantining  and screening is the  buyers responsibility  as well... even if the dealers is a good dealer that does  some of the above  this is not an excuse for  avoiding quarantine at home.”


Last Updated on Tuesday, 07 September 2010 20:46