Toads in our pond

Question
We have a small pond, about 1000 gallons, with 2 small koi and 2 larger koi
fish and about 15 guppies. We noticed that since we introduced the larger
koi, our guppies have significantly decreased - I could only find two this
morning. We introduce the new koi a couple of days ago, and the smaller koi
have been with us for about 2 weeks.
My husband thinks there are toads eating the guppies, but I find it too
coincidental that the koi were introduced, and then the guppies disappeared.  
What are your thoughts? By the way, we live in Hawaii!
Thanks.

Answer
Toads in general do not eat fish.  They come to ponds just to spawn.  Koi though can and do eat smaller fish.  I think the koi ate the guppies.  Or, perhaps another predator like herons, raccoons, bullfrogs, etc.  Or, maybe they just died for some reason.  I suggest keeping your guppies in their own smaller pond away from hungry koi!  Good luck!