Sick Koi?

Question
One of my koi has been acting strangely.  A few weeks ago, I noticed a few round white growths on the very edges of its tail and fins.  It behaved absolutely normally and the growths went away.  Now the fish is hiding out most of the time, but when it does come out to eat, it occasionally does an odd jerky head movement. Any idea of what this could be?  All the other koi seem to be fine.  I have had my water tested and everything was normal, but it was on the hard side.  My pond is approximately 1300 gallons and I have 10 koi.  This one is around 10 inches, medium size for the koi in my pond.  

Answer
White blobs on a fish may be lymphocystis which is a virus.  It's not curable but it's not deadly either.  It also usually doesn't go away so that may not be the problem.  You can look on images.google.com for lymphocystis and see examples.  It could have been some other sort of cyst or perhaps a mass of bacteria or fungus on an injured area.  The jerking is common in sick fish in general and doesn't narrow things down much.  If your koi are all moderate in size, the pond is going to be a little crowded in the future.  I don't think that has anything to do with this one koi's problem if your ammonia, nitrite, and oxygen levels are fine.  It can be hard to diagnose koi problems.  The best way is to contact your local koi club and have someone look at the koi for you.  Good luck!

Robyn
fishpondinfo.com