Taken from liveaquaria.com:
"The Blue Paradise is a territorial fish that will defend its area from its tank mates. For this reason, it should only be kept with other large, semi-aggressive fish. It will also eat smaller tank mates. Adult males should be kept one per aquarium, as they fight as fiercely as Bettas."
These rules are sometimes only applicable to home aquariums due to the lack of space to establish territories, so it may not be an issue in a large pond. So is this pond still in the planning stages? If so, do you have a thread on the build? I'd love to have a pond of that size. One day, maybe.