1. The Fish, 2. The Pathogen, 3. The Pond Itself.:   Therefore, the key to avoiding disease is to identify and, when possible, remove or reduce the effects of these risk factors for each particular disease and many are common among many diseases!.

In human and economically justifiable veterinary medicine, these risk factors have been scientifically studied for many diseases by sophisticated statistical methods. For a particular disease, numbers representing degrees of risk or “odds” for those familiar with gambling, have been generated, and thses are ranked so that people and animal caretakers have prioritized lists of those things which decrease the chance of getting a particular disease. Now, the “odds” concept is extremely important, because it illustrates that prevention or production of disease is not absolute! Theoretically, it should be, but there are just too many subtle and ill-defined interacting variables to be absolute. In other words, getting a disease with all the risk factors present is not a certainty, just as avoiding the disease is not, but there are certainly some avoidable practices which will greatly reduce the chances of getting a particular disease.:  Okay, if you made it this far-congratulations, because it is a complex concept and I have only scratched the surface! So, what does this mean for your koi and your pond~Well, to my knowledge, there has never been a good study performed to try and define the risk factors that increase the chances of even our common koi diseases. We can, however, use some make a best guess at what these are for some of the more prevalent diseases. Let’s take Bacterial Ulcer Disease BUD for example. Here is my semi-prioritized list of what are the most important risk factors that contribute to this disease in your pond. Now, in presenting this list, please remember, it is not scientific! I would love to have the resources and time to more accurately work out the relative contributions of each factor. Maybe someday, but until then, these are open for debate, amongst hobbyists and veterinarians, alike! Each risk factor listed has a few brief comments attached and is worthy of a whole article itself-especially the first one. However, I am confident that if you work towards reducing these, you will go a long way to reducing not only the frequency of BUD in your pond, and also increasing the effectiveness of treatment. Many are related to each other, so in working to correct one, you will correct others.

2. Rapid change-any change!:  The fish physiology is extremely intertwined with its aquatic environment (it lives in its own toilet!). It is not good at coping with rapid change in pond water parameters. This is especially true for day-to-day fluctuations in temperature (especially in and out of that 55 to 65 degree F range). Also pH, oxygen, and other water chemistry changes can be very good water quality! Another important point about change and BUD, is that koi in a pond get used to the kinds and numbers of bacteria, viruses, and parasites that are present (disease causing ones and others)! The pond microbiology is a literal soup! A kind of balance gets set up. Changing this, whether by introducing new fish, or treating the pond with those “organic burners” (e.g.: potassium permanganate), can result in a whole new situation which the fish has to get used to, all over again! Be careful and minimize change to minimize BUD! Bigger deeper ponds are far more resistant to change than smaller and/or shallower ones.

3. Medium-Cold-Water:  It seems that some of the bacteria implicated in BUD (e.g.: Aeromonas sp, Pseudomonas sp, etc.) Have the upper hand over the fish at around 55 to 65 degrees F (also see above). This is probably because the bacterial machinery is more efficient at these temperatures than that of the koi’s immune system. If you can afford it, get a pond heater to minimize this risk factor, and keep temperatures consistent at 65-75 degrees F during those fluctuating spring and fall seasons.

4. Poor water quality:  No need to harp on the importance of ammonia and nitrite control, is there? Be careful in the fall when fish have grown through the summer; you are used to summer feeding amounts, and the efficiency of your biofilter is decreasing because of falling temperatures, Low total hardness and alkalinity may be extremely important risk factors for a number of reasons (a future article). Soft water tends to be prone to changing other water quality parameters (see 1!), and harder water is thought to aid in more efficient gill function.

5. Subsaturation Aeration:  Aerate well with supplemental airstones-especially as temperature rises in the spring, at maximum pond temperatures, and during the night. BUD bacteria seem to enjoy a pond where the fish are not experiencing well-aerated water!

6. Inadequate Water Movement:  Put some good current in your pond with a well-angled inflow or venturi! It seems to be good for the koi’s “well being,” as well as conditioning. The benefits on koi physiology can only be guessed at, but some have said that good current may cause koi to work more and thereby reduce stress (works for people - who am I to argue?). Also, there may actually be a phenomenon whereby a current reduces the effective “contact ratio” (a medical concept) effect of bacterial transmission between fish.

7. No Salinity:  Much has been said and written about the benefits of salt. Fish blood is at 0.9% and although they need a little bit of an osmotic gradient, reducing the work they have to do by keeping pond water at 0.1 or even 0.2 is a good idea. It helps the gills work better and bacteria and parasites don’t seem to like it as much!

8. High Fish Densities:  More and/or bigger fish results in: more waste, more bacteria (even from recovered shedding carriers!), and a chance for more change.

9. High Infectious Pressure:  Simply put, this means that high numbers of bacteria will make other listed risk factors even more important to control. REMOVE SICK FISH FROM YOUR POND TO YOUR HOSPITAL TANK as they will build up the infectious pressure and make other fish more susceptible. Identify the bacteria and treat early with a targeted pharmaceutical.

10. Type Of Bacteria:  Certain bacteria do not need the risk factors to be as out of balance as other bacteria do. The term is that they are “more pathogenic.” By identifying which bacteria your pond has been infected with can help determine how “off” the other fish and pond environment factors are.

11. Poor Immune Status:  A fish with a better immune status can stave off higher numbers of more pathogenic bacteria. The immune status of a fish will be affected by other listed risk factors. In addition, different individual fish/varieties (like people) at different times, will have more”robust” immune systems than others. Centuries of inbreeding appears to have made our current show koi less robust than the common carp. Is it now time to start breeding for form AND function? Also, the immune status is what a good vaccine is supposed to improve.

12. Mucusmembrane Disturbance:  The slime layer is the primary physical barrier in a fish to bacteria. It is colonized by good and bad bacteria (which can live nicely in a balance). It can be disturbed by crowding, improper handling, poor nutrition, and other risk factors. “Organic burners” can also remove a lot of it, meaning that the fish has to re-secrete and bacteria have to re-colonize (see 1).

13. Excessive Parasites:  By tying up the immune system, causing wounds, and disturbing the slime coat, parasites can make a fish more prone to BUD (as can parasite control medications!). Therefore, treat, but treat with caution.