But they're koi! Koi are vegetarians!. Well, supposedly...

We gave our daughter a small koi which she put in an indoor aquarium along with her tropical fish. She fed them all tropical fish food, which has lots of animal-derived stuff like freeze-dried brine shrimp in it. A couple of years later, the nice, passive, vegetarian koi had become a raging carnivore and had eaten all the other fish in the tank!

The idea of turning a half-acre pondful of five-pound koi into carnivores to get rid of some pesky neighbors and their yappy dogs does have a certain appeal. However, I do go swimming in that pond and I'm rather fond of all my body parts, especially the one the fish would be most likely to mistake for a leftover hot dog.