Well about 2inches.
We started to find dead fish with big gaping wounds on their sides. We could not work out was causing it and asked at our local aquatics and he said "Do you have frogs?" to which we had lots and he said they get on the backs of them thinking they are other frogs and erm ride them
Sadly the pressure they put on them, causes big gaping wounds on either side
Theres nothing you can do about it. We lost about ten or so fish within a few days. We no longer have a pond now as my dad was too upset by it as they were his fish. The frogs naturally keep coming back though:roll: