Diagnosing health problems in Koi Changes in behaviour and appearance are signs that Koi are unwell, however, alone they are not reliable indicators of any specific disease or condition. My Koi appear slimy and have a pink flush to the skin Slime is caused by changes in the mucus layer. It tells us the immune system is active and there are various reasons for this that range from easy to remedy health issues to serious diseases.  This means it is safer to investigate rather than jump to conclusions.  Poor water quality or a toxic substance in the pond water could give the skin a slimy appearance or a pink flush.  Check if there are signs of anything airborne around the pond it is amazing what the wind introduces to ponds. Has recent rainfall been acidic as this could cause a pink flush? Test the tap water for chlorine, chloramine and nitrate and the pond water for ammonia, nitrite, pH and KH. If satisfactory and the water is safe carry out small partial water changes with dechlorinated water in case there is anything in the water that cannot be traced never use chemicals. A parasitic infection can also create similar signs and keep in mind not all parasites cause the irritation that makes Koi flick. Take mucus smears if a microscope is available or ask a dealer to examine the fish to confirm if parasites are the problem. Treat the pond for the appropriate parasite if the water parameters are safe with the UV off. If neither water quality or parasites are the problem disease has to be considered. Bacterial diseases are very unlikely to attack all the fish simultaneously they spread far more gradually.  Some viral infections can make the mucus appear more like white patches than the normal layer. A virus can cause a more widespread reaction in Koi as well as skin changes the fish may be lethargic. It is easy to blame the last fish to take up residence in the pond when fish become unwell soon after introduction although new Koi are not always the culprit.  Never risk a pond treatment without testing the pond water first. My Koi flick, scratch on objects and occasionally dart around the pond Parasites are the most likely cause if the irritation is continuous. If it is only occasional it is important to keep in mind Koi flick morning and evening due to changes that take place in all ponds and they can also flick after eating and all such reactions are normal. Revealing which parasite is the problem means the appropriate treatment can be used. Always test the pond water when Koi are not behaving normally and take mucus smears to avoid the guesswork that leads to needless chemical exposure. A Koi jumped out of my pond and I salt bathed it but it did not recover was the bath a good idea? If a Koi takes a leap for dry land or you find a fish laid next to the pond always put it back in the pond initially.  The Koi will be in extreme stress and there may be internal injuries. The longer the fish has been out of water the more dehydrated it will be and the oxygen dissolved in the pond water will be very urgently needed. A bath in salt will increase the stress the fish is experiencing and will be of little help. I have known Koi keepers delay returning fish to water to topically treat the skin and even administer brandy which cannot help the fish and, in reality, it is the hobbyist that needs the stiff drink. If the fish survives, leave it alone to upright itself without being handled.  Skin damage can be treated later once the body is rehydrated and the stress has diminished. A topical antiseptic such as Tamodine by Vet Ark Ltd or Antibac by Kusuri Ltd can be applied later to prevent the body being invaded by bacteria and fungus.  Koi prefer to live with other fish and in the case of injuries only Koi that have serious skin damage or are unable to swim normally need isolating in a hospital tank.  The water parameters need to be identical to the pond, an airline to provide a high level of dissolved oxygen, and salt at ½ an ounce per gallon or 0.3% on a salt meter will help.  A mild bactericide such as acriflavine can be used with salt to help prevent secondary problems.  Without a mature filter on the tank water changes will be necessary with dechlorinated water without chilling the fish and the salt and acriflavine will need to be topped up. My Koi are listless yet water parameters good and no sign of parasites Increase the level of aeration to make the Koi comfortable whilst investigating the possible causes. Could very recent heavy rain been acidic and upset the fish?  Has a new item of equipment or a health product been used in the pond recently? Has the tap water been tested for chlorine, chloramine, and nitrate? Has a horticultural product been used adjacent to the pond?  Have new fish been introduced recently? If the tap water is known to be safe carry out small frequent water changes with dechlorinated water even if the pond water test results were satisfactory in case there is an alien substance in the pond. Koi rest on the floor of the pond At low water temperatures Koi will sit or lay on the pond floor and this is normal behaviour.  However, when inclined on one side for very long periods the fish are chilled.  Chilling of the swim bladder is due to temperature fluctuations rather than the water being very cold as it is in winter.  This is why spring is a common time to observe Koi on the pond floor. However, the Koi should be seen to swim around when the sun has warmed the pond even for a short period. Isolate any severely affected Koi that is never seen to swim at all in facilities that can be gradually heated.  Use salt in the water at 1/2 an ounce per gallon or 0.3% on a salt meter and raise this to 1 ounce per gallon or 0.6% after 24 hours.  Koi that are prone chilling prefer to live in shallower warmer water. At higher water temperatures if Koi rest on the pond floor for long periods this suggests the fish feels unwell and there are many possible causes. My Koi suddenly swam frantically and then floated on pond surface liminate the possibility of electrocution if a circuit breaker is in use this is unlikely. When the electricity supply to the pond is known to be safe ensure the dissolved oxygen level is high.  Has a pond treatment product been introduced, if so, drain some pond water and top up with dechlorinated tap water without chilling the fish? Has a horticultural product been used, or is a device that emits copper for the control of blanket weed used continuously or at low temperatures? Serious disease can cause odd patterns of behaviour as the disease progresses to a new phase. Extreme parasitic irritation usually triggers scratching behaviour and whilst this can become excessive frantic activity bumping into the sides of the pond is usually a more serious problem. My Koi are irritated, have a soapy film, and brown gill filaments. The most likely cause is nitrite and this suggests the pond water is not being tested regularly for ammonia and nitrite. An overstocked pond, insufficient filtration media, an immature filter, cleaning the filter too much, the over use of chemicals are all possible causes of raised nitrite and other water quality issues.  There are interactions between the water chemistry and the biological life in the filter system that can gradually kill filter bacteria and the only way to know if the pond water is safe is by testing pH and KH, as well as ammonia and nitrite. Carrying out water changes with dechlorinated water and ensuring the dissolved oxygen level is adequate will help the fish revive. If the water parameters are satisfactory parasites can also create mucus, however the brown colour of the filaments is a classic sign of brown blood disease due to nitrite poisoning. Several Koi are suddenly misshapen or bent Possible electrocution check for faulty electrical equipment and if the circuit breaker is working.  Lightning can also trigger injuries particularly to the spine of Koi that were on the pond surface. Electricity and lightning cause serious damage that is irreversible. If a pond treatment has been used very recently or a toxin has found its way into the pond the damage will vary depending on the chemical. The skin, the major organs, and body systems such as the nervous or endocrine system are commonly damaged. For example, organophosphates such as Masoten which, although illegal, is still sold on line can cause the body to bend. Whilst Koi can recover from some types of toxic exposure, the damage caused by organophosphates is irreversible. One Koi has raised scales and protruding eyes The fish most likely has dropsy which is not a disease, it is a condition with several underlying causes.  Koi can be helped by living in salt at ½ an ounce per gallon 0.3% on a salt meter to help reduce fluid retention. If after 24 hours there is no improvement, the salt can be increased to an ounce per gallon or 0.6%.  Once the scales are almost normal, further treatment may be required depending on the cause of the dropsy.  If the cause is bacterial the fish may be listless or there may be an area of redness on the body. Antibiotics may be appropriate and their use is safer for the fish when the scales are no longer raised.  In spring, fish can develop dropsy in reaction to seasonal changes. If the fish has, a good appetite, mixes with the other Koi and the body is back to normal bacteria may not be implicated and the fish can be observed to ensure the improvement is sustained.  When many Koi in a pond all develop dropsy, this indicates a more serious form of disease and advice is needed. My Koi are sulking and have small black spots The most likely cause of black spots is Argulus or fish lice.  View the body closely as the spots will move if they are lice.  However, if there is no movement and the spots are more like small black cysts firmly attached to the body seek advice as there are other possibilities.  Young lice are hard to detect, however, filling a glass with pond water and giving the particles in it 10 minutes to settle to the bottom of the glass might reveal the very tiny juvenile lice darting around. These will mature into adults in days depending on the water temperature and early treatment with a product specifically for fish lice is recommended. A Koi has an irregular shaped wound Possibly an injury.  The wound should be topically treated with an iodine based or other antiseptic product. Sharp objects are rare in ponds and it is a fact that Koi know how to avoid them.  Has the fish jumped and damaged its skin, or could a heron or cat have caused the injury? Bacteria and fungus can gain entry to the body through any wound so monitor the fish and retreat if healing is not observed. Ultimately antibiotics may be required when a wound does not heal.  Consider if the pond design makes it easy for heron to access the pond. Heron will only enter shallow water and then release a substance to attract the Koi.  Mink and other wildlife can also be a problem to Koi in some locations and raised ponds can be the solution. Several Koi have open sores that do not heal An injury usually involves one Koi.  When several Koi all have some form of skin damage this suggests bacterial disease. A newly introduced Koi can bring infection to a pond although such cases are less frequent than those triggered by poor filter maintenance methods as they are the number one cause of this type of disease.  Only in the very early stages can the disease be cured by treating the pond with Chloramine T or similar product and applying an iodine based product or antiseptic to the skin lesions. Ulcerative forms of bacterial disease are difficult to control if the Koi are left untreated. Immediate action is required as once the disease is advanced antibiotics are required and it is common for them to be used unsuccessful unless used in a full treatment regime. See articles on Aeromonas and antibiotics on this website. My Koi have a few raised scales in patches This is possibly a scale pocket infection. If the condition is widespread with several Koi infected, treat the pond with a bactericide, chloramine T is a good choice for this type of infection. If only one fish has a patch of raised scales, a topical treatment with an iodine based product can help ensuring it can get under as well as on top of the scales. My Koi jump morning and night and this concerns me The reaction is seen at specific times of day, so it will be due to the water chemistry and temperature changes that take place in all ponds every morning and evening. If the Koi had a parasite problem, they would be the flicking and flashing continuously, not intermittently or showing other signs or irritation such as changes to the mucus layer.  No action is needed as long as the jumping is restricted to these times of day. Small bones protrude from the body of newly purchased Koi although there is no sign of skin damage This is most likely Lernea or anchor worm. Remove the parasite with tweezers taking care not to break it leaving one the anchor end embedded in the skin.  This could cause localised infection as it leaves the skin open to disease. Dab the skin puncture with an iodine or another antiseptic and observe the fish to ensure it is healing. One or two anchor worm does not mean the pond needs chemically treating. Only the female anchor worm embeds in the skin, all other stages of the life cycle die off therefore breeding may not have taken place at all or be possible in future. If only one new fish was infected by the anchor worm good observation may be all that is needed to ensure it has not spread.  It has become a less common parasite in recent years. The Koi gill rate is fast and gill cover does not close fully The water quality should be tested for ammonia and nitrite and dissolved oxygen. If the results are satisfactory a few Koi should be examined.  Sedate the Koi and if a microscope is available take smears carefully inside the gill covers although never directly from the filament.  Check for gill parasites such as Dactylogyrus or gill fluke. If no microscope is available look closely inside the gill with a magnifying glass.  The filament should be deep red not white, grey or brown. Usually there will be heavy mucus in the gill cavity and on the filament if parasites are present.  Gill inflammation due to parasites and secondary infection by bacteria and fungus is likely and is a common reason for the gill being unable to close. If the infection has been in progress for some time there may be signs of tissue destruction and the gill rate will alter. The gill fluke egg hatches at summer water temperatures adding to the burden on the gills if an outbreak is underway. If gill fluke or another parasite is found, the pond should be treated.  Skin fluke can be controlled with less treatments then gill fluke as they are egg layers more treatments will be needed.  In cases when no parasites are found in either gill cavity or on the body it is wiser not to introduce any chemicals. When Koi are unwell, medications they do not need can make the health problem worse.  A disease in progress could cause similar signs to a gill fluke infection. A Koi dealer can advise on various fluke treatment products. Fluke Solve based on praziquantel is now available in a Plus formulation that is more effective and there are Flubendazole based products such as Fluke M. You advised against mixing Koi from different countries due to viruses. Is CNGV still circulating and if Goldfish live with Koi can they both get KHV There is no pattern that helps hobbyists understand the complex nature of viral disease in fish. There are millions of fish species each with its own susceptibility to disease including viruses. A good example is the Carp family as many members can contract the virus that we call carp pox although few suffer with Koi Herpesvirus or KHV. Goldfish and Koi are both Carp family although they are not predisposed to the same viral diseases although can both develop carp pox and the diseases caused by poor living conditions. Some years ago in Israel, a virus thought to have a larger genome than is found in most herpes viruses was named CNGV. However, a genetic link was made with the disease that later became known as Koi Herpesvirus so CNGV is not in general use. Israel produced an attenuated virus vaccine to protect their Koi production and in order to challenge the vaccine the Koi were housed in lakes and exposed to live KHV.  Whilst KHV outbreaks were controlled in Israel, the vaccinated Koi they exported triggered outbreaks and carriers of KHV introduced the potential for future outbreaks into many ponds.  It was due to this situation that I recommended in various articles that housing vaccinated Koi apart from existing healthy Koi is the only way for Koi keepers to protect existing healthy Koi. Israel no longer vaccinates all their Koi production and it is important to keep in mind that KHV is in all Koi producing countries including Japan. Koi keepers should always establish the origins of any Koi they wish to purchase from the seller so they do not put their Koi at risk of KHV or other diseases. Listless Koi refuse food, hover under the surface and look misty White spot is one possibility particularly if new Koi were recently introduced or if the pond water temperature has suddenly changed as this is a major trigger for white spot.  The spots resemble grains of salt and as the numbers increase the mucus is disturbed and the skin develops a white filmy appearance.  The changes in the behaviour of the Koi are often seen before any spots appear. The parasite can kill so treat the pond for white spot without delay. All water quality issues should be eliminated and other parasites investigated if white spot is not identified.  There are specific treatment products on sale or malachite green and formalin can also be used for this parasite. My Koi are gasping at the pond surface Although Koi cannot obtain oxygen for circulation around the body by gasping at the surface, this action usually indicates the pond water is low in dissolved oxygen.  This happens in hot weather, in planted ponds, when chemicals are used and as Koi grow larger their need for oxygen increases.  Using an air pump and air stones is the best way to increase the oxygen level as a fountain or waterfall are less effective at creating the right type of oxygen. In an emergency, if the fish are gasping, turn on the hose pipe. Whilst tap water contains chlorine and chloramine a dechlorination product can be used once the fish have recovered.  If the fish do not improve within a few minutes, oxygen depletion may not be the problem.  The pond may be polluted and draining some water out and topping up with dechlorinated water may help.  Take care never to chill the fish, as tap water is colder than the pond water for much of the year. My Koi has a round white growth on the body that is getting larger Growths are very common in fish and as they have different causes this makes a definitive identification by Koi keepers impossible.  The most likely cause of most white growths is carp pox - see the next question.  A diagnosis based on pictures alone does not provide enough information to confirm the nature of any type of growth or cyst, an examination or even a biopsy is often needed.  Dermocystidium Koi causes growths and this disease is frequently misdiagnosed on the Internet and this causes undue concern when in reality it is rare disease.  There is an article on the website that explains more about this disease. There are white lumps on several Koi If the growths are white, wax- like, a little glossy, and firmly attached to the body, the condition is most likely the viral disease carp pox.  This can also form a layer on the skin and does not always present as a perfect round or oval growth. No treatment is necessary, it is a disease of cold water which will diminish as temperatures rise. Mature Koi are far less likely to develop the disease and it seldom causes complications.  If warmth fails to alleviate the virus in juveniles, this could be a delay in the immune response that will resolve with age.  White growths are a common observation in Koi and not all are due to carp pox. My laboratory needs to examine a fish to diagnose the nature of cysts and growths. My Koi have dirty white tufts on their skin and are listless White patches are a common observation on Koi yet they can have different causes. If material resembling dirty cotton wool is seen on the skin, it is likely to be a fungal infection. Fungus is always secondary and only attacks skin damaged by injury, disease, parasites, chemicals, or poor water quality. Treating only the fungus will not cure the underlying problem so it is necessary to find out what is wrong that allowed fungus to infect the fish and there will be skin damage. My Koi rise to the surface and gasp Low dissolved oxygen is the most likely cause. The air that we humans breathe contains the oxygen we need and we take a breath in order to be supplied. Our Koi, however, need their oxygen dissolved in the pond water and the extraction process uses up their stored resources as it requires energy. A waterfall makes large bubbles however, this is not the type of bubble that can enter the gills in Koi and pass through the membrane into the blood vessels. An air pump and air stones are far more effective and creating the right type of bubble. It is often overlooked that the available oxygen is lowered by pond conditions, the weather, treatment products and with temperature rises. As conditions change, the dissolved oxygen available to the fish decreases and the fish may rise to the surface and gasp.  This behaviour is deceiving as Koi do not take oxygen into the gills at the surface, they can only obtain it from the water. If Koi are always at the surface possibly the dissolved oxygen is too low.  The fish will gasp at around 3 mg/L when resting, they need 6 mg/L and 10 mg and over to be active. Larger Koi need more dissolved oxygen as they grow and when Koi are added the level should be increased. The pond filter is full of life that also takes oxygen as do pond plants and in most ponds the Koi have to get by on what is left. The colours of my Koi are dull It is a fact that some Koi health problems can reveal themselves in the skin and their normal vivid colours can become dull until the fish recover.  The use of salt also dulls colouration if Koi are living in it for too long.  However, even Koi in perfect health can have a genetic history that does not support their colour cells and this can alter as they grow and age with little chance of improvement. Pond water conditions particularly pH can have an impact on colouration and each Koi variety have their own unique requirements in respect of water chemistry. This means in a pond home to mixed varieties of Koi some will not have the appropriate support for their colour cells.  Diet is important and Koi need variety with some natural foods as well as pellets that contain spirulina.  Pond conditions are just as important as an adequate diet.  Mature fish will never regain their youthful appearance once the skin deteriorates and some varieties mature far better than others and are often the less colourful or mono coloured Koi. When dull skin colour is accompanied by lethargy or food refusal then a health problem is more likely. Why is chlorine in tap water no longer removed by holding a hose high over a pond? Nothing has changed it was always a myth that anything harmful in tap water was dissipated as it went through the air before reaching the pond.  Many Koi keepers still follow this advice and the fish will be exposed to chlorine and chloramine which are both harmful to fish. Pond water would need to be agitated not just circulated in bright sunlight for possibly two weeks depending on the levels in the water to breakdown the chlorine and you cannot do that with fish in the pond and chloramine is even harder to remove. This is why there are dechlorination devices and products and hobbyists need to ensure that whichever method they use they are removing not just chlorine but also chloramine.  When filling a new pond, it is vital to remove all unwanted substances before the fish are introduced.  When topping up the pond whilst the contents of the tap water will be diluted by the volume of pond water there can still be unacceptable levels in the pond. It makes sense to test the water in both the tap water and the pond regularly with DPD4 tablets. These tablets are unlike the normal tests Koi keepers use. Any colour change is viewed direct by looking down into the water sample not through the side of a test vial.  Any hint of pink in the water sample indicates that chlorine or chloramine is present. Is it wise to treat ponds spring and autumn to prevent health problems? This myth implies that spring always initiates Koi health problems serious enough to need treatment irrespective of how well the pond is managed and how healthy the Koi living in it are.  A routine treatment in autumn suggests fish are not in good condition after summer and that is unusual in most ponds.  Routine treatment subjects Koi to chemicals unnecessarily, and risks killing the pond and filter biology. In ponds, that are well maintained and new Koi properly quarantined before introduction the use of chemicals should not be necessary.  Naturally there are different approaches to the hobby and those who enjoy visiting various aquatic outlets to select Koi rather than buying from one Koi dealer, and those who favour less pond maintenance are likely to use more treatment products.  How ponds are managed is personal choice as long as fish welfare is paramount. Why is spring difficult for Koi keepers? Spring is a time for cleaning and Koi keepers need to ensure that after all pond and filter maintenance the system is flushed to waste for several minutes. It is important that no water from the filter that could contain disturbed matter is allowed to return to the pond immediately.  Failure to take this precaution is the prime cause of certain forms of bacterial infection.  Other forms of disease due to bacteria differ in how and at what time of year they occur. Spring is only a problem is some ponds due to the fish coming out of their dormant period at the same time as other aquatic organisms due to the warmer water. Ponds and filter systems vary greatly and therefore how good hygiene is put into or practise will differ although the principle is the same. It is a myth that filter systems in heated ponds pose less of a risk of harbouring harmful bacteria as the same advice on maintenance applies to all ponds. Whilst spring is the time for extra caution in all ponds when cleaning filters the hygiene measures recommended should be in use whenever the filter system needs maintenance. Koi are lethargic mucus thick cannot see any parasites with microscope It could be a Costia infection and as it is very small parasite some struggle to identify with a microscope. Make sure the light is not too bright under the glass slide. Costia is seen at a lower magnification although it should be clearer at X400. It resembles a comma on a page that looks as if it is constantly going head over heels.  Costia can kill although small it can access all areas including the gills. Outbreaks of costia will vary from cases when the whole pond is infected to a pond in which only one Koi has costia.  It is likely that fish will have another underlying health problem or it may simply be a weak fish. My Koi are getting parasites from frogs and birds Organisms found on Koi are all referred to as parasites although some are free-living that do not actually parasitise Koi, they live on the fish not off the fish directly.  Fish Lice and fish leeches are true parasites they need their blood for nutrition and can spread disease. However, trichodina and skin fluke whilst not parasitic can cause irritation and as Koi try to relieve it skin damage could result. Costia has phases when it lives in harmony with Koi and is harmless until it changes its lifestyle. There are millions of fish parasites although in Koi the common species are fairly easy to identify and treat, it is the less well known that can be stubborn. Perfectly healthy Koi introduce most parasites to ponds, as there is no other route for transmission.  Do not blame a Koi dealer for nature in action unless fish are heavily infested with parasites on the day of purchase.  Birds and frogs could introduce certain parasites such as fish lice or leeches to ponds.  However, they would have to leave the infected water and arrive at the clean pond without delay. The immune response in the bird or frog will kill off the parasite and they are not acceptable hosts for aquatic organisms that cannot survive without water. Should I use formalin or formaldehyde in my pond? Formalin and formaldehyde are not identical substances.  Formaldehyde is a gas at room temperature and formalin become the aqueous form of formaldehyde when combined with methanol. It is available in various grades for numerous uses. Chemical companies offer generic substances such as formalin, malachite green, potassium permanganate and others for various purposes.  However, selling them as generics for use with fish is illegal.  The government cannot stop the sale of these materials although they are trying to control the way they are advertised so as not to suggest inappropriate use. The safe way to treat a pond is by purchasing products manufactured under the government scheme that ensures all generic chemicals are of the highest grade, quality controlled, and have directions for pond use on the label. No license is required for products sold under the scheme and manufacturers base dose levels and directions on established usage and as sources differ, any variation in doses between brands is acceptable.  The most used pond treatment products are formalin that removes the mucus layer and malachite green is used in conjunction for protection while the mucus layer is missing and to bathe the skin and, as Koi are valued pets, they deserve safe treatment products. Why do you not suggest a series of general Koi treatments to see if they cure problems My laboratory advises anyone involved with Koi with caution as it is vital to avoid guessing what is wrong with fish when no examination has taken place. Koi reveal signs when unwell that do not indicate a specific disease or condition. They stop eating, spend time in abundant oxygen, or may hover nose down irrespective of the problem and this behaviour does not suggest a diagnosis only that the fish are unwell.  If a general treatment such as malachite and formalin was suggested and fails to cure the problem, we would be asked what to try next and this can lead to over treatment.  It is also likely that more than one person will be asked for advice and this can cause confusion.