UK Koi Policy Unit






Dr. Paula Reynolds


What is biosecurity?
It requires the active participation of everyone involved with Koi at all levels to make biosecurity fully effective.  Biosecurity is neither a straightforward concept nor a single set of rules.  It is a wide range of measures and practices that have to be adapted to individual situations with the aim of minimising disease risks at every single stage in the life of Koi. It should be applied from the moment the egg hatches right through to the management of the pond in which they will remain for life. The regime adopted by hobbyists to avert the introduction of disease to the pond is just as important as, by then, Koi are much loved pets.

Why do we need biosecurity in Koi?
When Koi from various sources meet, pathogens they carry are exchanged.  A pathogen is any agent that is harmful and this includes parasites, bacteria and viruses. In many cases, both groups of Koi acquire the capacity to resist each other’s pathogens.  Some diseases require very specific incubatory criteria to be met before they materialise and this depends on various factors, principally water temperature.  A lower temperature example is Cyprinid Herpesvirus (CHV), often termed carp pox; whereas a higher water temperature is required for an outbreak of Koi Herpesvirus (KHV), a disease which has caused a lot of concern around the world in recent years.

Biosecurity individual

Individual units for each batch of koi is
the only way biosecurity can operate

Why involve hobbyists in biosecurity?
The more hobbyists appreciate the need for biosecurity, the more likely the Koi Industry is to support the major initiative that is now needed.  Koi-keepers are at one end of a chain that is only as good as its weakest link.  When a farm is run on a biosecure basis, the farmer accepts responsibility for the health of the fish produced and sold.  Koi are often prepared at a central point before export, and if this is not run biosecurely, the protection afforded by the farm is wasted. Everyone involved in the Koi supply chain; exporter, importer, wholesaler and dealer, raises the standards of the Koi Industry by becoming biosecure.

In addition to preventing the spread of health problems, a good biosecurity system should flag up exactly where a disease has originated and stop further shipments of Koi from any infected source.  This requires precise record keeping and must include all the Koi stocked and their location on site.  Their origins and shipment dates are also important, and the system must make clear what stage each Koi has reached in the quarantine process. Those dealers holding Biosecure Certification through the Professional Koi Dealers’ Association are able to offer this degree of accountability to their customers.  This level of care is time consuming and costly as biosecurity requires policing at every stage and on a regular basis.

Cross-infective risks
Cross infecting a healthy aquatic system can happen in trade premises or the garden pond.  Introducing fish actually suffering from disease is just one possibility; however, fish can be asymptomatic carriers showing no signs of a health problem. It is equally possible that a carrier has lived in a pond for years but the disease has not broken out for a variety of reasons, principally that the criteria required has not yet been met.   Whilst water temperature is the prime factor, there are changes that have to take place in the body of a carrier fish before an outbreak can occur.  The complex scenario that results from any virus such as KHV makes tracing the carrier difficult as the last fish introduced may be the suspect that turns out to be innocent.

Biosecurity dealers

Dealers have to make clear
they are biosecure

Mixing Koi from varied sources
Koi-keepers participate in biosecurity by several means, most important of which is the quarantine of new fish. Diseases do not need a passport to travel around the world and in reality all new fish pose risk factors. The more that is known about the history of any Koi will increase its safety to some degree but the information must be verifiable.  A separate pond is vital for Koi known to have been exposed to KHV and therefore carriers, as they cannot live with naive Koi. Hobbyists need to be aware that the status of vaccinated Koi is not identical to that of a carrier.  A virus is a pathogen that needs host fish in order to replicate so it is not surprising that farms were the first to be infected by the virus that later became known as Koi Herpesvirus . It was inevitable when dealing with a new viral disease that mistakes were made as greater understanding of the nature of the disease was acquired. Ultimately it was agreed that the disease we now refer to as KHV created the carrier state in those Koi that survived it and the earliest vaccine attempts sadly also perpetuated the disease.

Safer vaccines are now in use and on trial and they vary in how they work to prevent KHV outbreaks. Whilst antibodies have long been regarded as the best defence they can trigger outbreaks of certain types of disease when used in vaccines. The immune response in fish has many components other than antibodies that can also be harnessed to provide protection. The Kovax vaccine is currently licensed for use in Israel and therefore many of the Koi exported from Israel are vaccinated. This vaccine has not yet been approved for use in the EEC or USA. The universal adoption of a vaccination program gives rise to issues such as the human food chain. Koi are eaten in some parts of the world and this may make mass vaccination a problem. This type of vaccine does carry the slight risk of reverting to wild type KHV but this is difficult to calculate given the current safety record. In fact, in purely statistical rather than scientific terms, this particular vaccine may be safer than various other measures against KHV outbreaks in use in other countries at this time.

Herpes viruses are very common in fish and are encased in lipids for protection. These are fatty substances that in theory can be broken down by antimicrobials. However, in practice treating Koi suffering from KHV is unsuccessful  so prevention is the best way forward .The KHV virus has mutated and there are now several strains that add to the complexity of research. Although a generalisation, most survivors of KHV can live with one another irrespective of the strain. It is important to appreciate that KHV is now in most Koi producing countries. A further reality is that carriers and vaccinated Koi irrespective of which vaccine they have received may be living alongside naive Koi. Each country has policies in place that whilst not uniform in approach have none the less considerably lowered the incidence of KHV outbreaks. Whilst there were fewer outbreaks of KHV in the UK in 2010 a risk still exists and KHV is not the only disease for consideration when promoting biosecurity.

Why change temperature during quarantine?
There is no foolproof method of initiating any disease during quarantine and, whilst there are numerous health problems other than KHV, the seriousness of a virus suggests every possible precaution should be taken.  The use of heat alone is not always sufficient unless the criteria for KHV are already met within the body of the carrier Koi.  That is why both chilling and heating are needed.  The water temperature at the outset of quarantine will vary with the ambient temperature depending on the time of year and, in most situations, heating equipment will be required. The difficulties of achieving low temperatures in summer are obvious and, for most hobbyists, this will require frequent water changes via a purification unit. Koi must be constantly monitored, no matter how gradual the temperature changes are carried out, to ensure parasites such as whitespot are not becoming a health problem.  Many Koi naturally carry whitespot without any sign at all until a change in temperature acts as the mechanism that initiates an outbreak.

Biosecurity separate

Designated areas for the
examination of customers’ koi
and water samples is essential

What temperatures are required during quarantine?
At the outset of quarantine, the water temperature should be held at 15/16°C for 24 hours then very gradually increased over approximately 7 days to a minimum of 23°C, maximum of 27°C and then held for 3 weeks. The temperature should then be taken back down slowly to 15/16°C for another 24 hours, and again with care not to stress the Koi, taken back up to a maximum of 27°C and held for another 2 weeks. If disease of any kind has not developed during that period, it is possible that the Koi have never been exposed to any serious disease such as KHV and are not carriers.  It is important that the application of heat ramping in search of KHV should not be regarded as reliable scientifically. A virus has the capacity to hide within the body of the carrier fish.  However, in research it has been found that the more chill/heat cycles Koi survive without any disease developing, the less likely they are to test positive for the KHV antibody.  This suggests that whilst the use of heat ramping is not foolproof it is still a greater safeguard than taking no action at all.

How long should quarantine take?
There is no time scale for the quarantine period as it will vary with the Koi-keepers’ ability to control the temperatures and the health status and reaction of the Koi, although three months is considered viable. On the day the quarantine period is finally over, it is vital to ensure that the water parameters in the quarantine facility mirror those of the pond. The pH and temperature are especially important. Having taken the Koi through this type of quarantine, the move to the main pond must minimise the stress associated with any change of environment.  The equipment used in the quarantine facility must be separate to that used for the main pond, and hobbyists need to remember to wash their hands after contact with the fish or water in either system.

Biosecurity surfaces

Every surface in the quarantine area should
be made of material that can be sterilised

How valuable is a health certificate?
Buying Koi, certificated KHV free, from any country is a good policy as it may have some validity.  However, a certificate does not always mean exactly what the wording seems to imply. Often it is a generalisation, rather than specific details, that apply to a box or consignment of Koi, and some health certificates cover more than one farm which is impossible in biosecurity terms. It is also fact that biosecurity is not a concept that is fully appreciated and it can be seen as restrictive.  Some farms cannot implement it because the changes are too costly or difficult. Due to the nature of the tests currently used in some countries, the certificate means far more in terms of protection for Koi dealers and hobbyists than it does in others.  The housing of Koi after testing in non-biosecure facilities away from the farm would score low in a professional biosecurity audit and yet is a common practice. There is no international standard approach to the use of certification. Koi-keepers are therefore recommended to buy from a safe source such as PKDA Certified Biosecure Dealer or quarantine new purchases, irrespective of any certification available at the current time.  

Where do we go from here?
Viruses are so complex that those who study them often believe they have unlocked all their facets when, suddenly, along comes a new insurmountable aspect of the pathogen and a lot more study and experimentation is required.  What the Koi Industry needs is the time and the financial resources to be able to eliminate, not just KHV, but other serious health problems and funding is a major issue as it has to come from those who produce and care about Koi.  Biosecurity must become acknowledged as the primary safeguard even when the risk of KHV is over as there are other viruses and serious diseases that will become the new threat.  It is the way forward for the future of the Koi industry and hobby.

What options do hobbyists have?
The safest option is to purchase Koi only from dealers who hold Biosecurity Certification, in order to reduce the risks considerably, and then quarantine for a shorter period of time away from trade premises for added protection.  This period can be shorter than was recommended earlier in this information for Koi from a non biosecure source, four to six weeks is usually sufficient. There is no reason to give up the hobby or stop buying Koi.  It can be satisfying to see fish thrive during quarantine and, when the process is over and healthy Koi are living in the pond, the Koi-Keeper can relax in the knowledge they have applied every safeguard.





  • Water temperature changes are a common trigger of KHV.
  • Koi are usually lethargic, refuse food and exude excess mucus.
  • During an outbreak signs can include changes to skin, gills and behaviour.
  • In some cases Koi suffering KHV may have very few signs.
  • Some Koi appear to resist the disease but later test positive.
  • Mass mortalities do not always occur.
  • The last Koi purchased may not have introduced the disease.
  • Raising the temperature speeds up the outbreak but is not a cure.
  • Outbreaks are more common when quarantine is not carried out.
  • The risks are reduced when purchasing from specialist Koi dealers.