Something ate my fish :(

We have a really cool koi pond on the side of the house and since it got cold the fish disappeared. We just assumed the fish were hibernating in their small cave. Today, however, we had the guy who installed the pond for the previous owners come over and he told us they should still be visible, even this time of year. We can't get in the cave to see if they're still there because if they are we could shock them to death. The pond guy pretty much gave us no hope that they're just asleep, though, suggesting instead that a heron must have gotten them. The cave just isn't that big to fit all six of them without a tail or two poking out... My poor husband is all sad; he'd named them and everything.