If you have taken the sensible precaution to build a quarantine system it should be away from the main pond and you should have separate nets, buckets, bowls, etc and the two should never meet! Needless to say, you should wash your hands between quarantine and pond visits.

So what is KHV?  KHV is Koi Herpes Virus and is highly infectious. There is no known cure at present, although some work is being carried out to see if immunisation is a possibility. This may increase the capacity of the Koi’s immune system to fight off this particular pathogen.

KHV usually needs a water temperature of between 18 – 27oC (62 – 80oF) to bring the virus out. It takes about 12-14 days at optimum temperature to show itself. The symptoms vary with water/temperature conditions and the only sure way to find out what is killing your fish is to sacrifice an infected but live Koi for euthanasia and autopsy.

Generally early signs are lethargy, lack of feeding and excess mucous. These symptoms can of course be found with other diseases, water conditions or parasites; Whitespot being a prime example. Water problems should also be eliminated at this stage before despair sets in.

A virulent outbreak will progress to the shedding of mucous, white blisters that eventually burst, bleeding from the gills and necrosis of the gill membranes.

An outbreak will usually result in a mortality rate of 75 –80%.

Survivors will be those Koi genetically closest to the common carp. No surprise there then that your favourite Go Sanke is almost bound to go!

As there are no treatments at present, nor are there likely to be any for some time, what happens when the outbreak is over?

For a total wipe out the solution is to empty the pond, powerwash and disinfect it along with the filter system. You could also consider replacing the filter media. Refill the pond with clean water, through a water filter, and leave for about 4 – 6 weeks before introducing new Koi. But do remember to add to the collection slowly (and via a quarantine system) so that the new filter can keep up with the increases in ammonia, etc..

If some of your Koi survived you still need to sterilize your pond and filter system. Removing the survivors to a quarantine system would allow complete sterilization, as for an empty pond. If that is not practical a heavy dose of Potassium Permanganate should do the trick. (Remember Potassium Permanganate must not be used in ponds with plants and heavy organic content.) Leave the survivors in peace to recover for as long as possible, but at least 8 weeks if you can’t wait any longer. Make sure you quarantine all new fish and if possible put them through a cycle of warm water whilst in quarantine to see what effect this has upon the Koi.

Having re-read my draft I see that I have used the word ‘quarantine’ 7 times. Prevention is better than cure, and in the case of KHV, the only option. So please quarantine all your new fish before popping them into the pond with all your favourite Koi or you never know you might lose the lot!