FROG KILLS KOI IN UK POND
 

We have had the exact same experience. The frogs killed all our fish by clinging on to them. I tried to prise them apart with no joy. We now keep our pond purely as a wildlife pond with no fish, which is better for wildlife anyway.

FROG KILLS KOI IN UK POND
 

I have the opposite problem, not that I like frogs. But one of my larger koi grabs the frogs by the leg and carries them around the pond until they die. Then just toys with the dead frog like a child with a teddy bear.
I've had koi for a good few years and never seen this before.
Anyone seen this behaviour?