RE: My pond fish are disappearing - is it the frog?
How big are the fish in your pond? How big are the frogs and what species are they?
Most frogs are not known for eating fish, but some species of frogs will swallow anything they can fit into their mouth, just like most fish species. So it is hard to say until we know what exactly species the frogs are and the sizes difference between them and the fish.
There can be other possibilities. Are there raccoon in the area? Raccoon are known for fishing from the ponds and outdoor fish tanks. They can be the one eating your fish.