I’ve just had this happen too! But the frog wasn’t gripping the gills it had actually lodged its legs into the koi’s eyes!! Yes it’s eye sockets! How in gods name it had done it I don’t know but I literally had to prise this frog off my koi and pull its front legs out of the koi’s eye sockets! It’s dark right now so I can’t check my fish over easily but fingers crossed it’s alright? It swam away but there must be damage? I fk hope it survives. I’ve never seen or heard of the before! I’m guessing the only reason the fish isn’t dead, it that the frog didn’t attach to the gills and suffocate the koi. Maybe that means she can survive albeit properly blinded