Monogenetic Trematode



There are many parasites that infect ornamental fish, but the ones that seems to instil fear in the minds of koi keepers are flukes

Flukes belong to Monogenetic Trematode parasitic flatworms genus. They exist in Many forms and infect a many varieties of fishes.requiring only one host to complete an entire life cycle, For our purpose's we will be discussing the main variety gill fluke and skin or body fluke.

Before we get into this subject lets clear a little misconception up,
The term gill fluke does not mean they are only to be found on the gill lamellae, they are just at home on the main body of the koi. And the same is true of body / skin fluke.

Gill Fluke.Dactylogyrus

Gill fluke are hermaphrodites meaning they possess both female and male reproductive sex organs, thus a pond devoid of all parasites (if such a thing can ever exist) that encounters a solitary fluke can soon, if conditions prevail for that fluke to thrive, be overrun with fluke.
There are about 100 subspecies the two main common species that are encountered by the koi hobbyist are D. Vastator and D. Extensus, both require a very slightly different temperature range but both are equally damaging to fish.
The morphological difference between gill flukes and skin / body flukes is that gill flukes are oviparous meaning egg laying protozoa's, and because of the complexity of their life cycle are difficult to fully eradicate
Gill fluke are microscopic let me repeat that! *microscopic* and cannot be seen with the naked eye, so if you are told otherwise, you now know.
However fortunately for us these critters can be seen quite well in great detail at low magnification X40/X100 no more than this magnification is required for identification purposes.
It will be noted that gill fluke has a typical worm like appearance and is fastened to the epidermis by a foot like device, on the foot arranged around the edge are very small sharp hooks called haptens, the fluke uses these to move across the gill or body and anchor itself to the koi.At the other end of the tube the anterior, are suckers that is used for the intake of food and nutrients, these can also be seen as the gill fluke stretches and contracts as the fluke ingests food matter, the fluke is capable of doubling in length as this pulsating action takes place. This accompanied by two sets of paired eyespots making four eyes spots in all at the sucker end of the fluke.

Flukes function in extreme temperature ranges and can be quite adept even as low as 6 deg Celsius and there is no know upper limit to their operating range of temperatures.
As mentioned before the gill fluke is an egg-laying parasite and treatment is a little difficult as it is very much a case of which came first the chicken or the egg
Newly emerged flukes, are fully free swimming smaller versions of the adult and must attach to a host within around 24 hours or so or perish, this is applicable to all temperature ranges once the fluke has hatched. Once attached they very quickly start the reproduction cycle and disperse eggs into the environment, but this is very temperature dependant, at low temperatures the fluke will only release one or two eggs per hour, however as the pond temperature rises to typical summer temperature ranges this will increase to over 20 eggs per hour and beyond.
It must also be noted that in real cold climates both adults and eggs can lay dormant for up to six months until the temperatures favour them.
Fluke eggs hatching rate is also temperature dependant at low temperatures they will take months to hatch and can indeed lie in waiting for the temperature to rise, or at summer temperatures will hatch in about 4 days, this makes treatment extremely difficult in the case of Dactylogyrus, but not impossible, so donít worry,

Skin fluke Gyrodactylus

Skin fluke are also hermaphrodites possessing both female and male sex organs. Where this fluke differs from the gill fluke is, they are termed viviparous meaning it gives birth to live young, a fully formed smaller version of the adult,
Upon microscopic inspection of a skin fluke you will see a slightly fatter version of the gill fluke with no eyespots evident and although the small array of small hapten hooks can be seen you can also see a pair of particularly nasty, very large pair of hooks formed into a classical H shape which Gyrodactylus uses for anchorage on the body,

These primary hooks will be very evident upon inspection and will probable be the very first thing you notice, thus it will always stand out in your mind and be remembered,
Typically as you look to the middle section of the fluke you will notice the unborn fully formed embryo and inside that yet another identified by those large single pair of primary hooks,
The skin fluke is a little like those little wooden Russian dolls where on taking the head section off there is yet a smaller one inside, so in one adult skin fluke, there can often be seen several generations of fluke, one inside the other.
Reproduction in skin fluke is also temperature dependant in much the same way as gill fluke although skin fluke do seem more able at reproduction at lower temperatures than gill fluke.-

Both skin and gill flukes if conditions are right will find a host and start reproduction and usually live for about a month and then perish, but of course by then the colony of flukes have increased many, many times.
It should also be noted that although both are parasites in the strict sense of the word they do not feed on the life's blood of the host but merely attach to the fish and feed on what passes by (dead cells etc). And provides no benefit to the host.

So why do fish die from fluke infestation?

As previously described the both types of fluke have a serious set of grippers (hooks)

And these are laced with very virulent inoculate pathogenic bacteria, so as the fluke moves around and secures itself on the host the hooks will puncture the surface of the koi's skin or gill lamellae. This in most cases will cause an Aeromonas / pseudomonas -infection, which can at best lead to a bacterial ulcer (hole disease) and at worst bacterial gill disease (BGD), the latter of which is as near to a death sentence for the koi as is possible, as BGD is very difficult to cure and takes a lot of time and dedication to correct, its also a fact that by the time the damage is usually notice the damage is already done and beyond repair.
There is no upside to the damage inflicted by fluke.


If the life cycle of Gyrodactylus and Dactylogyrus is full understood treatment becomes much or effective and predictable, it must therefore be understood that save one treatment a single treatment alone will not eradicate gill fluke, so we must employ multiple sequenced treatments the time span of which will be determined by the water temperature, since we are aiming to catch the emerging hatchling fluke as well as the parent,
The parent is easily dealt with by many treatments, potassium permanganate, formalin, chloramines T or Masoten, The latter of which is restricted in its use being an organophosphate, but ultimately has been over used by the Japanese breeders in their endeavour to over come fluke infestations and as such we have seen a mutation of fluke that can survive Masoten exposure
Formalin whilst being effective treatment in many ways is a very efficient consumer of valuable pond water oxygen, and therefore as the koi may have compromised gill function would not be a first line choice of treatment.
(Antibiotics do not eliminate flukes or any other parasites) just I case you were wondering, they only work against bacteria.

Potassium Permanganate
Potassium Permanganate is useful for gill and skin fluke control at the rate of 1.5 gm per ton of water (220 imp gallons) or 1.5 ppm( parts per million)
In order for this treatment to be effective against any fluke the typical colour of an active dose of PP (bright pink) must remain pink for at least 4 hours,
The activity of Potassium Permanganate, is influenced by the organic load of the water
Potassium Permanganate is an oxidizer and will oxides anything organic it comes into contact with for our purpose this can and does work against us as we treat, in some cases where a high organic load is present Potassium Permanganate will spend itself on the organics dissolved in the water and exhaust itself before an effective time period has elapsed to treat the parasite
I.E. the dirtier the higher the organic load, quicker the pink of the water goes to a tea brown colour, thus the pp is spent and of no danger to anything.
If this occurs a second half dose of the original dose @0.75 gm per ton should be administered and hopefully a longer duration to a total of 4/5 hours of pink can be achieved to damage and kill the fluke.

Word of warning!!!

Potassium Permanganate at the dose described above, is only a dose of 1.5ppm, thatís 1,5 parts Potassium Permanganate to 1 million parts water thatís how powerful Potassium Permanganate is. A dose of 2 to 3 ppm can be tolerated by koi but you are now in the land of, will it kill my koi or wont it?
The author does not recommend any other dose than the 1.5 gm per ton of water and a further half dose if it turns a very definite brown colour before 4 hours have elapsed.
Further to this it is important that the original dose is very definitely brown in colour, failure to observe this colour protocol will result in an overdose and very dead koi!!!

Two more observations, always know you pond volume before hand and gm weigh the dose precisely, there is no other way to administer this chemical
If you do not observe volume and weight dose protocol exactly the best that will occur is, at best you will under dose and achieve nothing and at worst overdose and kill koi, so be warned!A handy tip when using Potassium Permanganate is to keep on hand some pond dechlorinator or sodium thiosulfate, which is to be found in most commercial dechlors.
If for some reason you take your eye off the ball and over dose and the koi come skyward gasping, it should be noted that if you treat the whole contents of the pond with a standard dose of dechlor it will neutralize Potassium Permanganate in seconds and the whole mess will turn brown rendering the occupants safe from the effects of the Potassium Permanganate oxidisation process.

When treating for skin fluke with Potassium Permanganate two doses of the above dose of 1.5 dose per ton, spaced five days apart would be sufficient to eradicate skin fluke, and its probable that one dose would suffice as when you attack the adult skin fluke you also attack the unborn fluke, thus one hit with PP will usually eradicate both adult and unborn alike.

When treating gill fluke it is important to catch the emerging hatching fluke, and this can best be achieved in temperatures above 17/18 deg and a sequential doses of the above 1.5 gm per ton, spaced five days apart for 3 treatments maintaining the active pink colour for a minimum time period of 4 hours and no more than 7 hours at one time.

Chloramine T

Chloramines T is another good choice for skin and gill fluke and in many ways as long as the ph value of the water is 7.5 or above is quite forgiving on the koi but not the fluke
Dose at 2 gm per 100 imperial gallons on days one, two and three, leave for seven days and do a one off dose at 2 gm per 100 imp gallons,
There is an additional benefit of the use of Chloramine T in so much a it will reduce the bacterial count both in the pond water and also at 2 gm per 100 on the fish
Once again if your fish show any sign of stress to a C/T treatment dechlor will neutralize the effects of Chloramine T.

supaverm is an oral sheep drench for intestinal worms in the afore mentioned sheep.And has been developed for use in koi
This is the ultimate big stick against both skin and gill fluke requiring only a one off dose as it destroys the eggs as well.
However this substance is restricted and is hard to locate, plus in the UK it is illegal to use a wormer for any other beast other than that for which it was originally intended for use on, having said all that it is available from various sources usually at exorbitant prices, but as said already it is the last word in fluke treatments

Dose at 1 ml/cc per 100 imperial gallons. As a one off treatment administer over three to four hours spreading around the pond, after 48 hours do a couple of 15% partial water changes over a couple of days
Be warned!
Supaverm may stress and burn the fish in some cases, it will burn the intestine of the fish and as a result the fish may redden and show typical stress in this case do a partial water change, the koi usually bounce right back with renewed vigour

For a further fluke treatments see the paper on TELMIN under new fluke treatment on the home page.

To sum up if upon the discovery of one fluke or even a few fluke across a selection of slides taken from a selection of koi chosen for examination under the microscope. provided the koi are looking alert and no infections are evident there should be no cause for concern, a healthy koi in a healthy environment with a healthy immune system will carry the odd fluke with no ill effect this is both quite normal and natural for all carp in general and no cause for concern.
If however you are counting multiple fluke on each and every mucus scrape under microscopic examination this should set alarm bells ringing even if the koi may behaving normally for your pond situation, that something is out of the koi's normal control. (and only you will know this)In time or when pond parameters or pond temperatures take a turn for the worst the koi could and probably will come under a very real threat from flukes.