Are your fish clean? Do they have parasites, or have they been mixed with a contaminated batch of fish that have shown problems? There is a saying among fish dealers: “All fish dealers are liars except you and I, and I’m not so sure about you!”
You purchased your koi, so now what? Do you put them straight in with your other fish, or do you separate them and check for problems?
Over the years, we have received tens of thousands of fish. And, over the years, we have lost tens of thousands of fish due to the simple fact that shipping stresses the fish. Long flights are hard on fish. Many times, the shipper will not purge the fish before sending them to us, so ammonia builds up in the bag and weakens the fish’s immune system. Parasites can proliferate rapidly. Then, an opportunistic bacteria or virus will set in, causing sores, making them unsalable and sometimes even killing the fish.
The best way to not lose fish is to quarantine. Your better fish suppliers will heed this warning and not send out diseased fish. (You know which ones they are by reputation.) The tank needs a separate filter system with adequate circulation, filtration, oxygen supply and a cover. Fish will jump, and generally it’s the pretty ones that jump out first.
The day the fish arrive, I have a protocol for quarantining that lasts six weeks. Keeping the fish in good shape starts when the bag is opened. I set up a separate tank for new fish with a temperature within 10 degrees of the bag temperature. The water should be treated with salt, about 4 to 6 parts per thousand (ppt). If the temperature in the bag is not close to that of the tank, I acclimate the fish by floating the bag in our water until the water in the bag is within 10 degrees of our quarantining tank. These bags will generally have a high ammonia smell. Never mix this water with your quarantine tank water; remove the fish and place them in the new water. If the ammonia level is high, I also treat the tank with nitrofurazone for six days to heal the gills.
Visually inspect the fish for problems. I specifically look for bruising, missing scales and sores. At this point, there are two easily viewed external parasites — fish lice and anchor worm. These need to be treated with Dylox or Dimilin, since they have a chitin shell that is hard for most other chemicals to permeate. I treat for these parasites three times — once a week for three weeks to account for the eggs they can lay while in quarantine.
You need access to a microscope; you can’t diagnose what you can’t see. Using a cover slip and slide for a scope, I get three samples from 10% of fish received. I gently get a gill scrape, a mid-line scrape and top fin (or dorsal fin) scrape. If you see anything moving other than fish slime, like gyrodactylus or dactylogyrus, a treatment of formalin with malachite green or praziquantel are used. These are commonly called gill flukes. Notice the fish hooks at the bottom of the body. These will typically cause a tear in the fish’s gill or body where bacteria will opportunistically enter and cause further fish distress. I treat for five consecutive days, with a water change after the third dose.
Bacterial treatments are the third-tier protocol. Potassium permanganate is used in a straight five-day treatment to eradicate some gill parasites, fungal infections and bacteria. I mix a 2-ppm dose and add it to the water. The water should turn a clear pink color. Once the color has changed to a brownish color, the effectiveness is generally over. Clearing of the water is easily done with a follow up of hydrogen peroxide. Potassium will kill all the bacteria in a filter, so when treating, it is wise to set the filter on recirculate until the treatment is finished. We recommend that the filter be aerated during treatment, or the beneficial bacteria will die off if not sufficiently aerated. Potassium will also clear or polish the water and kill algae. Be aware that oxygen levels can drop in the water when algae are no longer producing oxygen.
The fourth-tier protocol is for aeromonas bacteria. Upon inspection of the body, if large, red sores are found, these are possible beginnings of aeromonas bacteria. These can cause small or large holes in the sides of fish, which can and will be fatal if not treated. Oxalinic acid is used for three days and is frequently successful in stopping the bacteria.
The last-tier protocol is to wait. There are fish viruses that cannot be treated and can manifest after a short period of time. Many better fish vendors will send off samples to veterinary colleges to get results stating they do not have the dreaded KHV, or koi herpes virus. This virus manifests itself when the water is under 80 degrees Fahrenheit. Presently there is no cure for KHV. There are several cases of complete populations of fish being killed after getting exposed to KHV.
I try to keep the stressors as low as possible all year long. Water monitoring is a constant task that reaps great rewards in making my fish happy and healthy. If a customer calls and asks why their fish are not eating — a first hint that something is wrong — I ask for the pH and ammonia levels.
Generally, I hear crickets on the other end of the line. When the test is eventually run, the pH is low, or the ammonia is high. These are easily regulated. A simple liquid reagent test kit gives more accurate results than test strips. Correct the problem!
After the quarantine period is over and the new fish are introduced to your pond, the work does not stop there. A quote from Dr. Erik Johnson still rings true today: “You don’t treat the fish; you treat the water. The fish will take care of themselves.”