Any changes to the environment have a direct and immediate effect on our koi. Changes greater or more sudden than what the fish has evolved to cope with - will result in stress. The environment, stress, infection and disease are inseparably interrelated. Studies on both cold water and warm water fish show that antibody production is lowered in the periods of stress. Ironically this is the important time when the body needs these proteins for defence.
Stress affects the immune response in koi in much the same way as higher animals.
However, in pond water there is much greater chemical and physical variability than exist in the terrestrial environment. Koi in our ponds are continuously affected by environmental fluctuations such as temperature and pH changes, ammonia, nitrite, nitrate levels, oxygen levels, etc. Other stressors such as excessive or rough handling, toxic materials dissolved in the water, drug treatments, water chemistry, population density, macro-organisms such as parasites all have an effect on fish and their immune systems. Fortunately, immune systems are constantly at work as an intimate and inseparable function of life. Koi live in a balance or equilibrium with their water environment.