The tanks are outside....but not ponds. Like an in-groud swimming pool sort of thing, with some pretty massive filration. Pacus, hmm, i am not sure about the legality of them over here in aust. I was looking at Arowanas, but arent they notorious jumper? I can imagine one ending up on the ground next to one of the tanks
. Clown knife would be interesting, but Ive only seen the one full grown one around near where i live, no more than that.
As for the aggressiveness of the Barra, they wont just attack stuff for the hell of it (ie. Jags), but if it is small enough to fit into their mouth, they will eat it. If you guys like, I can get some pics of the tanks sometime, so you have a bit better idea of the environment the fish have to live in.
Will ID sharks feed from the top? We have 2 large Tandanus Catfish, 70cm+, and we barely ever see them.
Thanks for the great suggestions so far guys, keep em up!