Deadly Viruses

A deadly virus is the one most feared of all fish health problems that can affect a retailer or breeder of koi and goldfish - not to mention the pond hobbyist.  When a virus is introduced into a pond with healthy fish they will all pretty much die and those who survive are declared "carriers" and must be destroyed.  A virus run amuck can literally devastate a whole population or of fish including our food fish.  That's why it is so important that we all take the responsibility to do whatever is necessary to prevent the virus from spreading. 

How to Recognize, Treat and Prevent Deadly Viruses in Your Koi or Goldfish Pond

There are several kinds of deadly viruses known to affect goldfish, koi and other fresh water fish.  Some attack only koi while others are not as discriminate.  Viruses stay with the fish for life (or death as in many cases).  Some koi and goldfish may come through a viral infection without harm.  A lone survivor, however, is a spreader of the virus and must be destroyed before he is exposed to other fish.

Viruses are not as common now as they used to be.  Government intervention (to protect food fish) and importers who go through a certification process to insure that their koi or goldfish are virus-free have really cut down on the number of cases.  This does not, however, mean that a virus cannot somehow find its way to your pond.  Viruses are spread from fish to fish and even a wet net can transfer the virus from one body of water to another.  

Recognizing a Deadly Virus

Deadly viruses are quick to kill and rarely leave survivors.  Viruses can lie dormant in cold waters and "come alive" once the water temperatures rise to a comfortable level.  If you add new koi or goldfish to your pond and within a day or two all your fish start dying off until only a few remain - and there's no other reason for it (ie. ammonia, nitrites or pH crash) - you could very well have brought a virus into your fish population.  If you introduce a new koi or goldfish to your pond while the water temperature is cold a virus may not show up until spring.  Let's say we get some really beautiful weather in April and the water temperature shoots up.  Your fish all of a sudden start dying "for no reason".  You've ruled out the obvious "mass killers".  You test the water for ammonia and nitrites and no readings show up.  Your pH is stable and your pond has not experienced a pH crash.  There is plenty of dissolved oxygen in the water.  This is the biggest indicator that a virus was brought in earlier and is just now rearing its ugly head.

The only sure-fire way of knowing if your pond has experienced a virus is to send a live surviving fish off to be tested for viruses.  There are a few Universities in the US that will test for viruses.  One of them is the University of Georgia.  You can call the School of Veterinarian Sciences and they can probably tell you how to go about getting it tested and what fees may be involved.

These were a few of the koi that were received at our water garden center with a deadly virus.  Because we are diligent about quarantining and treating our new arrivals this virus was not allowed to escape into our healthy population.  All the koi from this shipment died within a few days of being placed into a heated environment.  Notice that the fish seem to have no other symptom, no ulcers, no fin rot, nothing.  The Pond Doc checked the gills and they looked fine so there was no Bacterial Gill Disease.  Upon determining that it was a virus we contacted the breeders and sterilized our tanks and equipment that came in contact with the infected koi.

Treating Viruses

Sorry, guys, there are no treatments for viruses.  Viruses (even harmless viruses like carp pox) cannot be cured and will stay with the fish forever.  Preventing the virus is the only way to protect your koi and goldfish. 

If you suspect that you have experienced a deadly virus in your koi or goldfish population it is your responsibility to contact the dealer who sold you the suspect koi or goldfish and anyone who may have received any fish from your pond while it was infected and, sadly, you must destroy any survivors.  Just be sure that your pond is infected with a deadly virus and not a simple matter of ammonia in the water, pH crash or just that you forgot to add de-chlorinator before sacrificing the lives of any survivors.

Once the fish are all gone you will have to sterilize your pond.  You can basically "shock" it with chlorine like a swimming pool and keep that high chlorine circulating throughout the pond and filtering system for at least a week.  Then you can begin restocking the pond slowly.  Make sure to test for chlorine and use de-chlorinator if need be before adding any new fish to remove any chlorine that still might be present in the pond and filtering system. 

Emergency Procedures

1. Make SURE what you are dealing with is a virus and not a curable problem.  Test the water for ammonia, nitrites and pH and rule out poor water quality and pH crashes before concluding that it is a virus.  Make sure it wasn't something as simple as changing water and forgetting to add de-chlorinator.
2. Do NOT infect any other pond by giving away fish from the pond and alert anyone who has received fish from the infected pond.
3. Destroy any surviving koi or goldfish.  You may also send a live survivor to the University of Georgia for conclusive testing before destroying them all.
4. Sterilize the whole pond including any filters, nets, and other materials that have come in contact with the infected pond.

What to Expect Next

Once you've sterilized the whole pond you are basically dealing with a new pond and you will experience problems that new pond owners go through while seeding the biological filter.  Expect ammonia and nitrite spikes as your biological filter becomes established.  You are basically starting from scratch. 

Preventing Viruses

This is really your only defense against a deadly virus.  Place any new koi or goldfish in a heated quarantine tank for at least two weeks.  During this time you can also treat the new fish with a parasite pak so they are "clean" when they are introduced into your existing community. 

More Helpful Information

• Adding Koi and Goldfish in the Fall
• Humane Euthanization of a Pet Koi or Goldfish
• Seasoning a New Pond

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