Fish Care/Koi Herpes Virus (KHV)

Ecological Laboratories, Inc. thanks Dr. Julius Tepper for generously offering his broad knowledge of fish care in presenting this information.


By Carolyn Weise, Ecological Laboratories, Inc. and Julius Tepper, DVM, Long Island Fish Hospital, Shirley, NY

When I started collecting koi, I knew nothing and was blissfully ignorant. I think “blissful” was my key word here. And, why not? I was engaged in a prestigious new hobby, one with excitement, extravagance, danger. Back then, we had the Aeromonas and Pseudomonas infections to watch out for! We had parasites! We even had thieves who stole into peoples’ yards at night and stole their koi!

“Ignorant” didn’t mean much to me at that time. Nor should it. But in 1998, the koi hobby was irrevocably changed—forever. No longer can I (or any other koi collector) afford to be blissfully ignorant about quarantine when it comes to adding new fish to our collections.

The word itself has had far reaching effects. Shows have changed also. No longer do we have the luxury of viewing all the same-size category showa in one tank, but the judges now have to go the length of the showroom floor to judge the merits of one fish against another in order to protect the contestants from communicable and fatal disease. In 1998, immediately following a koi show at Hofstra University, NY, many ponds were wiped out due to a new disease, yet unnamed and undiagnosed. I bought three fish at that show and was one of the very lucky ones. I did not experience any sickness or loss following the show. It matters little from whence it came, but that it did come and it is an ever-present danger in any pond or show. We are no longer blissfully unaware. Precautions have been instituted, at least, at the show level.

Have you taken the necessary precautions at home? It is not just the imported koi that can be infected with KHV (as we now know it). No koi dealer is exempt from at some time in the future purchasing a “carrier” fish without his knowledge. It is not a guarantee that your fish will be safe simply by buying “only domestics”. Let’s look at what you go through when buying a new fish, and you decide.

When purchasing a new fish, the gorgeous fish in the dealers tank with the reported history of coming from his “own stock,” born last year (or this year) and he has never had any disease, all fish in his stock are treated for any parasites and are “guaranteed clean”…

  1. Do you ask any more questions and take a really good look at the fish in the bag, maybe have the dealer take a scraping for you?
  2. Do you take the fish home, float the bag on the pond until the water temperature is the same and then release it?
  3. Do you do a salt-dip and then release it into the pond?
  4. Or do you have a quarantine tank that will house the fish for the next 4-6 weeks (or longer)?

Well, if you answered anything but “4” you lose! KHV is not readily detectible unless the fish is already dying. The fish could be a carrier and infect all your other fish. How do you know the dealer knows the health of this particular fish and where did he get this information, or how do you know you can trust him if you have a pond full of beautiful koi at stake? Most of us would really prefer to believe the dealers are the experts so we don’t have to work so hard at protecting our fish. But it is your responsibility, not theirs. If you do not have a quarantine tank, get one. There is no koi owner with a “too small” pond to forget about quarantining new fish. Now is the time to think about the consequences of adding this one more, “cute little fellow” to your friendly, loyal bunch at home…..

A quarantine tank should be the cleanest water on your property. It should be deep enough and highly filtered, covered with a net to prevent escapees from succeeding, and close to a water supply. It should be close to the house where you have easy access and can readily monitor the fish. It should be large enough to accommodate sick fish (as they will grow) and should hold more than one fish. It will need an aerator too. It will be a basic hospital tank.

In dealing with KHV, you will also want to be able to raise and manipulate the temperature in this tank. Raising the temperature to 72ºF for two weeks will either bring out the virus or prove the fish to be negative, according to recent studies.

What must be impressed on hobbyists is that this virus must be treated like HIV in humans. Use universal precautions. Treat every koi as though it is infected. Gone are the days of floating the bag on the pond and then releasing it 20-30 minutes later, to watch the new fish explore its new home. Gone are the days of seeing several owners’ fish in one tank at a koi show. Until there is a cure, and unless another disease arises, quarantine is the only way to go!

Now, the tools of quarantine regimen are as follows:

  1. Holding tank
  2. Netting or cover to prevent fish from jumping out
  3. Small bio-filter, preferably pre-colonized with nitrifying bacteria
  4. Small pump with protective screen over intake, hose and all parts that can harm fish
  5. Dedicated fish net and bowl for quarantine tank only
  6. Dechlorinator
  7. Test kits
  8. Pond salt (Non-Iodized salt)
  9. Microbe-Lift/TheraP

The 21-day quarantine regimen is as follows:

[Note: The following dosages assume a 100 gallon tank. Adjust for your tank capacity accordingly.] This program originally designed by Water’s Edge has been modified and presented anew that many fish deaths can be prevented.
  • Day 1: After thorough cleaning of tank, refill with dechlorinated water and set up filter with pre-colonized filter media. Add 6 oz. of Microbe-Lift/TheraP, mix 1.5 cup of pond salt with water from the tank, then distribute throughout the tank. Add fish. (Note: Koi do not fare well unless there are two of them together.)
  • Day 2: Repeat above.
  • Day 3: Repeat above. Use salt level test kit to check the salt levels.

Our goal is to have a 0.3% solution by Day 3.

  • Days 4, 5, & 6: Monitor with water tests.
  • Day 7: Add 2 oz. Microbe-Lift/TheraP, check water levels.
  • Day 8: Add another 1.5 cup pond salt. Salt level should now be 0.4%
  • Days 9 through 21: Dose weekly with 2 oz. TheraP
  • Examine fish daily.
  • Watch for odd behavior: flashing, rubbing listing to one side, rapid breathing, or closed gills.
  • Look for signs of bacterial/fungal infections: white or discolored spots, fuzzy growth on fins, tail or mouth, discoloration around gills.
  • Check ammonia and nitrite levels every other day. If these levels are high, or if the water becomes cloudy, perform a 30-50% water change, as needed. Refill the tank with water from your pond. (This will dilute your salt level, so add more salt. The total salt amount after Day 8 = 6 cups or 0.4%. If you perform a 30% water change, add 2 cups back. If you perform a 50% water change, add 3 cups.
  • Feed sparingly (every other day) only as much as your new fish will consume in 5-10 minutes and remove any uneaten food. Remember, they do not have stomachs.


Maintain water temperature in tank at 72ºF for two weeks to bring out KHV in the event fish have been infected.

According to Dr. Julius Tepper of the Long Island Fish Hospital, some, but not necessarily all of the following may suggest a KHV infected fish:

  • Sudden death
  • Loss of appetite
  • Rapid “gilling”
  • Lethargy and slow swimming
  • Body sores
  • Areas of “dry” skin (feels like sandpaper)
  • Other areas with excessive slime production
  • Whitish dead areas on the gills

If any of the above signs are seen, contact a fish vet to arrange for KHV testing.

Now the day comes and the fish have passed all their tests. It is time to put them in the pond. Take a fresh bucket with fresh pond water, put fish in the bucket, carry to the pond, and gently release the fish into their new home!

Koi Club of San Diego is a 501(c)(3) organization, and all monetary donations are tax deductible to the fullest extent allowed by tax laws. Please check with your financial advisor if you have more questions. Tax Identification Number: 33-0355312

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