Do most moats have sharks or alligators?

A moat could possibly have alligators or sharks depending on the type of water.

Take your moat to be freshwater; it could possibly have alligators or bull sharks, probably it has nothing bigger than a carp.

However take your moat to be saltwater; there is a much larger variety of sharks that could inhabit it (bull sharks included again) but no alligators. I don't know of any saltwater moats, but they probably have nothing bigger than a goby. If the case is that you are considering swimming in a moat, do not hesitate. But watch out for boats.