Injury or disease?
 

As my water is getting a little clearer day by day, I can now see 25 of
my little fish. Today, while sitting out by the pond having a cup of
"Morning Thunder", I noticed one of my koi has what appears to be puffy
lips. None of the other fish seem afflicted. Does anyone know what
this condition might be and how it should be treated? Should I treat
the entire pond as a precaution or just isolate the koi? It is swimming
and feeding well.
Thanks for your input.
W. Dale