Quarantine – An In-depth Look

Quarantine is enforced isolation, usually to contain the spread of some kind of disease considered dangerous. The word, which comes from the Italian quaranta giorni meaning forty days, originates from the 40 day period of isolation of ships and people before entering the city of Dubrovnik in 1377 and was to prevent the spread of the plague, or Black Death.

Quarantine – An In-depth Look

Quarantine – An In-depth Look – This article was first written for and published by Koi Magazine in 2007

Quarantine is enforced isolation, usually to contain the spread of some kind of disease considered dangerous. The word, which comes from the Italian quaranta giorni meaning forty days, originates from the 40 day period of isolation of ships and people before entering the city of Dubrovnik in 1377 and was to prevent the spread of the plague, or Black Death.

The quarantining of new koi has always been a recommended practice as prevention against the spread of common parasitic and bacterial infections and has become even more important in recent years since the worldwide spread of Koi Herpes Virus (KHV). Koi, like all animals, can suffer from and carry disease and an apparently healthy fish may be harbouring some form of disease that may pose a risk to any existing population.

A good quarantine regime is as important, if not more so, to koi breeders and dealers as it is to hobbyists.  All koi farms need to bring in new brood stock to continue the improvement of the quality of the koi they produce.  For this reason they need to follow the same basic quarantine procedure as any hobbyist. Farms which buy fish in to grow on and resell at a later date need to be doubly sure that these new fish are free from disease, as they will most likely be mixed with existing stock before being sold on. Dealers have the same responsibility to their customers as breeders do to ensure that they have done everything that they can to provide properly quarantined fish that are as disease free as can be reasonably expected and should always carry out their own quarantine regime every time they bring in new fish to their establishment.

In an ideal world, every koi keeper would have their own quarantine facility and would quarantine every new fish they buy before introducing it to their pond.  If money and space were no object, a hobbyists quarantine facility would consist of a separate insulated building housing a dedicated quarantine tank of approximately 2000 gallons (this would comfortably cope with any size fish that would be purchased), including a bottom drain leading to a more than adequate filtration system.  The filtration needs to be able to react to large fluctuations in fish stocking density and medications.  The system should include a UV to help reduce the bacteria count within the circulated water and there should be a dedicated air pump to provide adequate aeration during medication procedures.  Ideally, the pump should be drawing air from outside the building. Either the air inside the building or the water should be heated (heating the air reduces any condensation in the building).  The building should have its own water supply and be equipped with its own nets and bowls.  Gloves should be used at all times when handling fish, water or equipment in the building so as to reduce the risk of transferring any disease to any other ponds.  The system should have some naive fish, (healthy fish not previously exposed to KHV) “Canary koi”, which serve the purpose of keeping the filtration system active, provide company for any new fish introduced and which also act as indicator fish should any viral disease be present in the introduced fish.

For the great majority of koi keepers however, the next step down from the full quarantine building would be to have a dedicated tank of 500 gallons or more and filter system that can be insulated to enable temperature ramping to be carried out. The drawback is that the tank will have to be covered to retain the heat and therefore observing the fish’s normal behaviour becomes more difficult. The other alternative would be to buy a collapsible tank. This has the advantage that it can be stored away when not in use.

To filter a 500 gallon tank my personal recommendation would be to use something like an Evolution Aqua Eazy Pod, which is designed to cope with a 2000 gallon pond (maximum) and will therefore be better able to cope with unusual stresses that it will be placed under.  This should be used with a pump that will turn the pond volume over in a period of 1 – 2 hours. The UV should be a minimum of 30 watts, with a 40 litre per minute air pump providing aeration to the pond. There are several ready made packages on the market and as long as you can find one that meets as near as possible these requirements you should be fine. If you have the skills to make your own quarantine system, you could build something tailored to your own personal needs that can fit into the space that you have available and should only cost a few hundred pounds.

Tap water should, ideally, always be passed through a de-chlorinator before it goes into a pond with fish in it since tap water can contain high levels or chlorine or other chemicals which can harm the fish or filter. The ideal water quality parameters would be undetectable ammonia and nitrite levels (below 0.05 when using a digital meter) and nitrate levels of less than 10 ppm with pH in the region of between 7.5 and 8. This is what would be ideal in any pond.

Once your new fish have been introduced to your quarantine system, a skin scrape should be taken to identify if any external parasites are present.  If any are found, they can be treated accordingly.  The temperature of the quarantine system should be roughly the same as the temperature that the purchased fish were kept in.  As soon as the fish has been introduced into the quarantine system, the temperature should be raised to (or lowered) and held at 15/16 degrees C for 24 hours and then raised to a minimum of 23 degrees C (maximum 27 degrees C) over the next three days and held for three weeks. The temperature should then be dropped back down to 15/16 degrees C for another 24 hours and again raised back up to the same temperature as before (23 – 27 degrees C) and held for another two weeks.  The intention with this process is to deliberately stress the fish in order to bring on an outbreak of KHV if the virus is dormant in any of your new fish. Once the temperature has been raised, feeding can start slowly, building up over a period of a week or two to allow the filtration system to adjust to the new stocking levels.  During any temperature ramping or after initial treatments, feeding should be stopped for 24-48 hours and again introduced slowly after this time.  It is important to monitor the water parameters particularly the ammonia and nitrite levels.  Regular water changes are essential at a rate of minimum 10-15% per week. Ideally the quarantine period should last a minimum of 6-8 weeks and at least until you are entirely confident that the fish are happy and healthy. Temperature ramping should be done as a precaution but any other medications for external parasites should only be used if they are necessary. If you add new koi during the quarantine period of existing koi, you will have to start the whole process again so it’s best to avoid doing this if you can.

The body language of your fish can be the first indication of any problems. A koi that is feeling unwell is likely to leave the shoal and hang around on its own.  The first signs of a problem are often one or more fins held tight to the body and the dorsal fin down.  The fish might also start breathing heavily.  This can be hard to see as it can be mistaken for chewing, so observation must be carried out at a period of time when the fish aren’t being fed.  The fish might tend to sit on the bottom, again with its fins in – this is a sign of stress.  If it sits on the bottom with its fins out, it could be a swim bladder problem or cold water temperatures. Flicking and flashing is a sign of external parasites, also the fish might shake its pectoral or pelvic fins or twitch its dorsal fin in irritation.    At the first sign of any irritation a skin scrape should be taken immediately to identify any external parasite. Excess mucus production, or velvet sheen to the skin, is a sign that things have gone a little bit too far and treatment is urgently required. If after several scrapes have been taken and no parasites seen, then the problem could be environmental such as poor water quality or untreated/contaminated tap water entering the pond. It could also mean that there is a more serious problem which could be bacterial or viral.  The signs would be fraying of the fins, open sores or bruising, reddening of the skin and visible blood vessels, raised scales and bulging eyes.  If the gills are looked at they could be pale and anaemic or have the appearance of being eaten away.  In this instance, and assuming that poor water quality is not the cause, it is very important to get veterinary assistance to identify whether the cause is bacterial or viral.  Bacterial infections can be treated with antibiotics and are a symptom of poor water quality and poor husbandry, either in your system or the one that the fish came from.  Viral infections such as Spring Viraemia of Carp (SVC) and KHV cannot be cured and have to be confirmed by a laboratory test. Viral diseases are an infection from fish to fish contact and are not caused by environmental conditions as bacterial infections are.  Observation is vital and 5 minutes monitoring at feeding time only is not sufficient.  Aeration must also be sited in such a way that observation can be easily carried out – just because a fish comes up for food, doesn’t mean it is a healthy fish.

Diseases are either caused by poor water quality, parasites, bacteria or viruses. Assuming your water quality is good and your filtration well maintained, the first thing to look for is a parasite infestation, which you can identify by taking a skin scrape and looking at it under a microscope.  The most common forms of parasites that affect koi are Costia, Trichodina, white Spot, and skin or gill flukes.  There are others but they are less common.  A microscope and a good koi health book, such as Duncan Griffith’s book “Step by Step Advanced Koi Diagnosis and Treatments”, will help you to diagnose which parasite is causing the problem and how to treat it.

Before introducing quarantined koi to your pond, make sure the water temperature in your quarantine system matches that of your pond.  Also, test the water in both systems to make sure that they are the same. Once you have introduced new koi to your pond you should monitor them on a daily basis as you should do with any koi as a matter of course.

After the quarantine period is over, and your new fish have been moved to your main pond, there should be no parasites within the quarantine system (white spot, fluke and Trichodina can live in the filter without a host for short periods of time) and if no bacterial or viral diseases have presented themselves then any naive fish can be left in the system to keep the filter mature and running.  If you don’t intend to keep any fish in your quarantine system, it must be completely drained down and cleaned.  This avoids any build up of “bad bacteria” within the system that could infect any new fish once the system is started up again. Products such as Virasure-Koi and Virkon Aquatic are great for disinfecting nets and equipment and using them should ensure that no bacterial or viral diseases that may be present in your quarantine system are transferred elsewhere. 

What equipment do you need?




Waterproof gloves



Treating mat


Parasite treatments

Wound healing kit


Good Koi health book

Top 10 tips for starting, running and completing a successful period of quarantine.

1) Wear waterproof gloves to prevent transfer of any disease or organism from entering or leaving the quarantine facility.

2) Maintain a clean environment in an around the quarantine system.

3) Frequent observation of the fish other than at feeding time.

4) Regular maintenance and monitoring of the filtration and water quality.

5) Regular water changes.

6) Immediate and effective treatment of any observed health problems.

7) Only treat once a problem has been identified and don’t be tempted to interfere with your fish if there isn’t a problem.

8) Ensure that temperature ramping is carried out correctly.

9) Don’t over feed the fish before the filter is mature enough to cope with the increase in fish and food waste products.

10) Maintain bio-security at all times.  Hands and equipment must not come into contact with any other pond and vice versa.

A time line that shows what you should be looking out for at each stage, when to carry out any water tests, water changes or treatments etc

Week one:  carry out a skin scrape to identify if any external parasites are present and treat accordingly.  Begin raising the temperature to between 15/16 degrees C.

Week two:  Ramp the temperature up to 23-27 degrees C and hold it for three weeks.

Week three:  Observe the fish and treat if necessary.

Week four:  Observe the fish and treat if necessary.

Week five: bring the temperature back down to 15/16 degrees C for 24 hours and then take it back up again to 23 -27 degrees C again for two weeks.

Week six:  Observe the fish and treat if necessary.

Week seven: reduce the temperature to the temperature of the pond that the fish will eventually be living in.

Check water parameters weekly and if in doubt daily.

How stress during transport and handling can affect Koi, what the overt symptoms might be, and how these are exacerbated and then relieved during a period of quarantine.

Koi are highly susceptible to the effects of stress.  Stress can be brought on when moving koi, both during transport and when being introduced to a new environment. When a koi is stressed, the autonomic nervous system releases adrenalin into the blood stream.  This increases the heart rate which also increases the blood pressure, breathing and metabolism.  Continued handling prolongs the exposure to stress and can lead to the suppression of the immune system and susceptibility to disease. On the other hand, it is important, since the discovery of KHV, that the fish are exposed to controlled stress (temperature ramping) during the quarantine process since the KHV virus only shows itself during periods of stress when the water temperature is between 18-27 degrees C.

8 disease symptoms and/or behaviour that might show themselves during a period of quarantine.

  1. Heavy breathing
  2. Excess mucus
  3. Flashing
  4. Clamped fins
  5. Sitting on the bottom of the pond
  6. Fish isolating themselves from the shoal
  7. gasping at the surface
  8. ulcers, bruising or raised scales

Jargon busters

Spring Viraemia of Carp (SVC) is a rhabdovirus that affects several species of fish including carp and koi.  Mortality is between 5 – 100% and any survivors then become carriers.  This disease has been notifiable for some years now.  This means it is a legal obligation to notify the authorities should an outbreak be confirmed and strict controls on the import of fish from countries where SVC is found have lead to outbreaks of this disease within the UK to be very rare.

Koi Herpes Virus (KHV) a form of herpes virus that affects carp (including Koi). Mortality rates during an outbreak are 80 – 100%.  Once infected, any surviving fish are likely to become carriers and can re-develop the disease at any point in the future, thereby infecting other fish that it comes into contact with. There are plans to make KHV a notifiable disease in the near future.

Temperature ramping is the rapid raising of the water temperature in an effort to bring on an outbreak of KHV.

A skin scrape is when a sample of mucus is taken from the body of a koi for examination under a microscope in order to identify external parasites.

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