Fish living in any body of water may be subject to parasitic infestations. This can be especially true for those living outdoors where natural introdution is possible.

The type of parasite and severity of infestation can vary but all will need treating appropriatly to prevent consequential illness developing. If an infestation is not caught in the early stages then it will be more difficult to cure later and the health of the fish will suffer. Their immune system may become compromised and they will be more suceptible to bacterial and other infections.

To avoid this situation it is neccesary to develop a good understanding of how your Koi behave when they are healthy. If they begin to show abnormal behavior, it will almost always be water or parasite related so, armed with your water test kit and/or microscope,  FIND OUT WHY  and rectify the problem.  DO NOT  just hope it will go away.