Question
I have about 40 fish in my pond, mainly Goldfish, comets etc and 1 Ghost Koi about 7" long. My problem is that quite a few of my fish are dying due to large wounds around the head, like something has taken a bite. Someone told me that it might be the ghost koi attacking the other fish, is this possible? Many Thanks,
Peter George
Norfolk
England

Answer
I highly doubt the koi has harmed the other fish.  Koi may sometimes eat fish much smaller than themselves but your koi is only 7" long.  I have two koi nearly 2 feet long with my goldfish of all sizes.  

It sounds like some predator has bitten at your goldfish who then died.  What is the shape of the wound?  If it's like a hole, it might be a heron or other bird poking at the goldfish.  If it's more like a mouth bite, it could be whatever mammals are native to your area (I'm not familiar with them).  A turtle is a possibility too if you have those.  I certainly wouldn't blame your ghost koi.  I don't even think it's physically possible for a koi to bite a chunk out of another fish.  The koi is either going to swallow a small fish whole, rip off some fins, or make a sucking type wound.  Your koi is just a baby itself, too small to do much damage.

Good luck with your fish!