love4aquatic
Fish Addict
You could keep a couple of marbled or albino clarias catfish in there although they are quite predatory towards smaller fish so any tankmates would need to be a good size.
Also just a thought but how steep are the edges? If the building is fully secure you could add a couple of yellow bellied turtles or similar,
I'm doubtful that they would travel too far from the pond so could be an option
Edit: Actually what part of the world are you from?
i am from the united states part of the world.
wouldnt the turtles pick on the fish?