Koi Health Information
Below are some of the problems that can affect Koi Carp. CLICK a link to give you the information on that particular problem.
A koi's health depends upon the environment. Koi have a high resistance normally and succumb to disease usually only after exposure to stressful conditions that break down the normal immune system. A stressed fish becomes a sick fish.
Stress is the main factor man has the most control over. Many disease causing organisms normally occur in the same environment as the fish. They usually only become a problem when present in significant quantities and/or stress occurs. Therefore, by controlling stress you can help maintain a healthy pond. Prevention is easier than treating your pond for disease.
Some causes of stress are:
- High ammonia level
- Low dissolved oxygen level
- Handling and/or moving fish
- Poor water quality
- Too high/low water temperature
- Other toxic chemicals (chloramines, oak blossoms, weed spray, etc.)
- Sharp edges in and around pond
- Inadequate and improper nutrition
Disease Agents: BACTIRIAL Flexibacter Columnaris (fin & tail rot). Aeromonas (hole-in-the-side). Pseudomonas. One of the principal causes of fish mortality is bacterial disease. Except for "columaris" nearly all bacterial infections occur secondarily to some other primary stress. Most are gram-negative organisms. Treatment: acriflavin, salt, etc. as a dip, topical, or pond wide treatment. PARASITIC Lernaea (anchor worm) Argulus (fish lice) Flukes Tricodina Monogenetic Internal parasites Most fish carry some parasites, but develop a degree of resistance that prevents problems. On the other hand, parasites such as anchor worms and fish lice usually are a problem whenever present. Young fish are more susceptible to illness caused by parasites. Stress situations and/or seasonal climatic variations may bring on infection. Some parasitic infections can be mistaken for bacterial diseases or viral infections. Treatment: Formalin, Malachite Green, potassium permanganate or salt in the whole pond or in a bath. Treating fish diseases is sometimes a haphazard affair because we do not always exactly know what the fish is suffering from. It is not easy to make a correct diagnosis Methods of chemical treatment: External swabbing Dip (five minutes in separate bath, aquarium) Bath (30 to 60 minutes) Sick tank or whole pond WHOLE POND TREATMENT Whole pond treatment advantages include apparent ease of administration and a desire to destroy all the harmful pathogens. The disadvantages are that biological filtration may be severely affected and treatments used tend to be absorbed by organic debris in the pond. In addition, therapeutic drug levels may not be reached as pond drug dosages are usually lower. LOCAL TREATMENT External swabbing with antibiotics and/or disinfectants can be surprisingly effective. The disadvantage is that the fish is exposed to handling and possibly anesthetics. Medication should be attempted after water quality and stress conditions have been improved. Partial water changes are very effective in improving water quality and relieving stress.
KOI HERPES VIRUS
Dr Paula Reynolds Aquatic Patho-biologist
Never jump to conclusions
Experienced dealers and hobbyists are well aware of the need to eliminate the obvious possibilities when Koi appear to die suddenly. Ammonia, nitrite and pollution caused by toxic substances leaching into the pond acid rain and even garden plants are all worth consideration whenever there are high mortalities in any pond or tank. In addition parasites such as whitespot have the potential to kill quickly and are an extremely common problem in newly purchased fish as Koi can harbour the whitespot organism whilst in perfect health and the new environment trigger an outbreak. Gill conditions associated with transportation often give rise to high mortalities. Only when all the likely causes have been eliminated should Koi Herpes Virus (KHV) be regarded as a possibility.
The signs of KHV
Koi Herpes Virus does not behave identically in all outbreaks and disease signs vary depending on how acute the outbreak is. Some Koi have little or no external indication of disease whilst in other cases the gills may haemorrhage, particles of gill tissue are shed, skin changes are observed and after death the gills are found to be necrotic. However the most common signs in nearly all affected Koi are lethargy, food refusal and excessive mucus. Water temperature is the main trigger factor in all outbreaks of KHV which occur between 18-27C/60-80F. Depending on the water temperature and the form in which the virus presents it can take 12-14 days or even longer for the infection to spread although it can break out sooner in situations in which all the incubatory criteria are met.
In order to diagnose Koi Herpes Virus it is necessary to sacrifice fish for post-mortem examination to eliminate all other possibilities and for samples to be tested. There are various testing methods that can be employed with a polymerase chain reaction test the most likely preliminary test. . This test requires a sample of genetic material from the fish containing DNA and this is replicated using polymerase material to produce sufficient DNA for analysis. The DNA sequences unique to a specific virus such as Koi Herpes virus are then revealed. In some cases if the PCR is positive for KHV a viral culture is then carried out. Despite the presence of inclusion bodies which strongly suggests a viral agent is the culprit, confirming KHV to be the actual causative pathogen is not possible in all outbreaks for a variety of reasons. In addition it is possible to test for the presence of the KHV antibody in healthy Koi but such tests can only reveal if the Koi have been exposed to KHV in the previous 6-9 months.
The spread of KHV
The mortality rate in most infected ponds or tanks is usually high although susceptibility to the virus depends very much on the genetic history and immune response in each exposed fish. Some Koi have a natural immunity to the virus and will appear totally unaffected and continue to feed whilst other fish around them are severely ill. Whilst the introduction of a new carrier Koi is the prime cause of an outbreak it is also possible for any Koi that has lived in a pond for years to be the carrier and disease did not break out until the incubatory requirements were all met particularly the appropriate water temperature, this is common in larger ponds and lakes. In such cases the disease is likely to cause mortalities in the new naive Koi so the disease progress is not identical in all cases.
It is no longer a safe practice to mix Koi from around the world together .Many outbreaks of what is assumed to be KHV are never confirmed scientifically but disease is now widespread in the U.K due to the continued import of Koi carrying the disease. Whilst KHV is the prime factor there are other heath problems that materialise when Koi from various sources are mixed in the same environment. It is safer to house valuable, prize winning or much loved pet Koi that are Japanese in origin apart from Koi from other sources as currently Japanese Koi are not deliberately exposed to it and are therefore, susceptible to the disease. KHV is highly infectious and sharing pond equipment, hospitalising fish for those without the facilities to care for sick Koi are a common factor in its spread.
Koi Herpes virus (KHV) as the name suggests is one of several herpes viruses which are the most common type of DNA virus causing disease in fish. The disease we commonly term carp pox, which causes the unsightly shiny white tumours in colder weather, should more correctly be called Cyprinid Herpes Virus (CHV). Only Spring Viraemia of Carp (SVC) which can affect carp including Koi is a notifiable disease in the U.K and CEFAS must be contacted if an outbreak of SVC is suspected. However, this disease is rare in a hobbyist’s pond so seek advice before contacting a busy government agency with what may be a common health problem. KHV is not a notifiable disease in the U.K.
Koi that survive KHV can pass disease on to any Koi from any source that has never been exposed to the disease previously. Therefore survivors of KHV should be housed apart and all equipment kept exclusive or they should be euthansed. The decision to euthanase every fish during a viral outbreak in case of a future incident must be a personal one for hobbyists but it is the only course of action in trade premises. Koi surviving KHV are not continuously infectious and only spread the virus during an outbreak of the disease. The time scale in between outbreaks varies and depends very much on the environment in which the Koi live and the fluctuations in water temperature. However Koi that have survived KHV rarely show signs of disease and as a consequence are not regarded as a likely source of disease. They appear very healthy but are in fact dangerous because they can fool both dealer and hobbyist.
Restocking the pond
It is possible to restock the pond with fish species that cannot contact KHV such as sturgeon and Orfe etc. In addition Koi from farms that subject their Koi to KHV before export can be housed with survivors and whilst KHV will break out the disease will be very minimal and the Koi likely to survive. The KHV virus dies very quickly in an empty pond devoid of all Koi however after a total mortality due to KHV if the Koi-keeper is anxious to restock the pond immediately power washing the pond and filter and then sterilisation with caustic soda or a strong disinfectant is advised. Possibly renewing the filter media is also a safeguard then after thorough rinsing the system can be restarted.
There is no treatment for KHV at the present time. Claims that cold sore remedies or massive doses of chloramine T actually cure are inappropriate as any resulting recovery from the virus is in fact a natural one that would have taken place anyway. Anti-viral pond treatments can be tried to reduce the severity of an outbreak and these can lower the mortality level. In some cases medications can be used to treat secondary health problems, which arise frequently to complicate both the diagnosis and the recovery phase. It can be beneficial for several reasons to raise the water temperature to approx 87F / 30C and hold it there for approx 3 weeks as soon as possible during an outbreak of KHV. This is not a cure but the disease will be over more quickly and as it is traumatic to observe the benefit is obvious although impractical for many hobbyists and irrespective the fish will still be carriers.
Our ability to control viral disease lies mainly in prevention rather than cure. Immunisation against some viral diseases is a reality in humans and animals but in fish, this is a fairly new field. Water creates an environment that changes the rules on disease transmission that apply to humans and land living animals increasing the potential for cross-infection. The susceptibility of each fish depends greatly on their genetic history and innate immunity. In addition, acquired immunity increases the capacity of the immune system to fight off pathogens including virus through exposure to disease as the fish matures. Although a generalisation the closer Koi are genetically to the common carp the more likely they are to survive a virulent viral disease, whereas we can predict that even inbred Koi will survive an outbreak of carp pox. Vaccines are currently being investigated along with other control measures in respect of Koi Herpes virus but this will take time to ensure they are legal, effective and safe.
How did my Koi contract KHV
High mortalities are a sad experience for any Koi–keeper and a financial burden for U.K. dealers and the world wide Koi industry. There is a tendency to blame the last Koi that was purchased whenever a health problem strikes when this fish is not always the culprit and in many cases it is the Koi that is least suspected that harbours disease . Newly imported fish pose the greater risk because of the variety of sources and the stress of environmental changes. That is why a period of quarantine is still a good safeguard and nowadays quarantining should be an accepted aspect of the hobby because of the increasing risk of all health problems not just KHV. Whilst quarantining lowers the risk posed by new Koi many outbreaks of KHV have been caused by carrier Koi already living in ponds and trade premises disease being triggered by increased water temperature .Whilst the carrier often survives it is the newer Koi naive to the virus that are killed. This scenario is confusing and makes it difficult to establish with certainty how any outbreak was initiated and it is this fact that has perpetuated the sale of carrier Koi preading KHV around the world.
Epidemiology - The science of disease transmission
DNA - Deoxyribonucleic acid-Genetic material found in most organisms
CHV - Carp Herpes Virus or Carp Pox
KHV - Koi Herpes Virus
SVC - Spring Viraemia of Carp
CEEFAS - Government Laboratory -Weymouth Dorset
Notifiable Disease - Classification of disease implying government must be advised of outbreaks but not applicable to KHV
Dr Paula Reynolds Aquatic Patho-biologist
Aeromonas is a genus of bacteria that includes many species capable of causing disease in Koi. Aeromonas salmonicida and Aeromonas hydrophila are the best known members of the genus but it is the latter of these two organisms that is of most concern to the Koi-keeper. The scientific community has mixed views as to the capacity of Aeromonas hydrophila to cause disease. Some regard it as an opportunistic pathogen, causing only secondary disease in Koi that are already in a susceptible condition. Others claim that it is capable of causing primary infection in its own right.
The hobbyists need proper guidance to deal with Aeromonas infections effectively as without proper management outbreaks commonly reoccur. However it is far more important to learn how prevent then becoming a reality in the first place. Understanding the many situations in which an outbreak of Aeromonas infection is most likely to occur demonstrates that Koi require stability, and when this is denied them disease often results with Aeromonas a very common enemy.
Causative factors in bacterial disease
- Recent importation is a major cause of Aeromonas infection
- Netting, bagging, transportation, rough handling
- The stress of a new environment
- Intermittent levels of ammonia or nitrite that goes untested by the hobbyist
- Prolonged periods of poor water quality when a new filter fails to mature
- Overcrowding increases the risks of disease transmission
- Fluctuations in p. H. and other associated water chemistry problems
- A lack of pond hygiene – No bottom drain fitted or the pond not hoovered
- A filter system in which fish waste and other decaying matter builds up
- Parasitic infestation that debilitate the Koi
- Exposure to harmful pond construction materials, heavy metals or toxins
- Heavy metals or toxins in the tap water
- Temperature fluctuations or the inappropriate use of heat
- Adverse spring conditions- water temperature fluctuations
- The use of too many chemicals in the pond can leave Koi susceptible
- Underlying undiagnosed health problem can predispose Koi to Aeromonas
- Failure to quarantine new Koi creates a further risk from Aeromonas
- An inappropriate diet leads can predispose fish to disease
- Injuries to the body caused by sharp objects in the pond can become infected
- A lack of sufficient dissolved oxygen in the pond allows disease to flourish
Avoiding every one of these potential trigger factors is impossible Koi have to be moved or no one could become a Koi-keeper. However, it is possible to look in more detail at each potential risk area and attempt to minimise instability for Koi as each situation arises. It is important to remember that Aeromonas is always present as part of the normal bacterial life of the pond and is found on the fish themselves and internally. Koi can never escape from it and it is the Koi-keeper who keeps this organism at bay by good pond maintenance.
Aeromonas can cause disease in a pond at a water temperature as low as 40F / 5C but he outbreak is usually less virulent. The higher the temperature the faster the bacterium multiplies and more signs of disease such as ulceration or reddening of the body will be observed. Losses due to septicaemia can be anticipated if the water is over 65F / 17C. This bacterium can multiply at an amazing rate if the temperature and conditions are conducive. In just one day one Aeromonas organism could generate well over 20 million more and 30 million is possible in really ideal circumstances. Each new bacterium will possess genetic material that enables it to resist the chemicals former generations of the species were exposed to in the fight to eradicate them. It is a fact Aeromonas know bout survival.
Ulcerative form of disease
The disease normally presents in the form of ulcers or open sores on the body, although reddening is also a sign of infection. The skin lesions are created by enzymes, which in this case are the metabolites or waste products of the Aeromonas bacterium. Once disease has become systemic and is affecting Koi internally usually only antibiotics are effective or the fish will not survive. However, if the disease is caught in time before what is termed bacteraemia has developed it is possible to control an outbreak with bactericides and topical treatment. The ulcer being open results in vital fluids containing electrolytes being lost from the body, the use of salt at 1/2 an ounce per gallon can help prevent this. Whilst the treatment of ulcers with topical medications will not cure a serious systemic disease it will help to prevent the further invasion of the body by other harmful organisms such as fungus and can encourage healing.
Aeromonas hydrophila is by far the most common subspecies causing disease in Koi and is frequently isolated in bacterial cultures along with Aeromonas sobria. Some species work as a team cleaning up after one another we can trust nature never to waste a nutritional resource. From the laboratory perspective Aeromonas hydrophila is a gram negative – oxidase positive rod with a singular polar flagellum. This means that the outer wall of this bacterium unlike some others will retain a specialist stain known as Gram’s stain which colours it blue. A further aid to identification is the confirmed presence of the enzyme oxidase. The term rod refers to the shape of the organism and the flagellum is a tail like protuberance at one end, which gives the bacterium its motility.
Aeromonas species whilst normally aerobic have the capacity to live in both aerobic and anaerobic conditions; we call organisms that can adapt in this way facultative. This means that the bacterium can hide in poorly oxygenated ponds or filtration systems harbouring decaying matter which can become a source of disease emerging at a later date when disturbed. Regular cleaning of the mechanical filtration chambers is obvious because their purpose is to trap debris but systems with voids beneath the media also need routine maintenance.
The filter system
Provision for flushing to waste after all cleaning procedures should be a standard part of all filter systems; a non-return valve incorporated into the filter plumbing prevents contaminated water returning to the pond. Cleaning should never disturb the biological part of the filter. There are biological pond cleaners on the market that use micro-organisms to naturally lower the level of dissolved solids and other unwanted substances in pond water. These can reduce the workload for the Koi-keeper when it comes to pond hygiene whilst at the same time lowering the risks of all disease including Aeromonas.
An uphill struggle in some outbreaks
Koi do not develop antibodies against Aeromonas species so the battle can become a long term one. You may cure an infection of bacterial disease with antibiotics and bactericides only to experience a new outbreak the following year. Koi will not stand up to prolonged use of antibiotics as the kidneys, liver and brain tissues can be damaged by their side effects. Resistance to antibiotics plagues all branches of medicine and is now greatly affecting the Koi industry and antibiotics should only be used under professional guidance. Koi culture is in a serious situation due to continued reliance on curing disease rather than preventing it. Aeromonas is not the only potential bacterium lurking in pond water, but it certainly is the most common.
It is possible to have a pond free of the risks posed by Aeromonas without resorting to any artificial aids. Such a pond will have a fully biological filter system with an excessive capacity to support the numbers of fish stocked any borderline system is inadequate. The pond must have sufficient water volume to allow each fish room to thrive 50 inches of Koi to 1000 gallons is an old statistic in Koi-keeping that still stands the test of time. This same pond will only be stocked from a quarantine facility never by direct introduction and it will be hygienically maintained on a very regular basis either through its drainage and filter system or by hovering. The Koi will be well fed on a good quality food including some fresh foods when water temperatures permit but no uneaten pellets will ever pollute this pond. Chemicals will not be used routinely only for a diagnosed problem and test kits will be in regular use to minimise all triggers factors. The kits used to test this pond should include dissolved oxygen because the wise Koi-keeper knows the vital role it plays in the well being of Koi.
Prevention over cure
It is vital for all serious Koi-keepers to realise that prevention is sager and more successful than cure when it comes to all bacterial disease in Koi and this particularly applies to Aeromonas infections. Having to resort to the use of any chemical especially antibiotics can only be seen as a failure to maintain the pond adequately enough to keep bacterial levels at a minimum, however when such drugs have to be used continuously to control disease the long term welfare of the Koi is seriously threatened.