I have a medium sized predator tank that I have set up and need some ideas for a center piece that fits the theme of semi-aggressive predator. I have a couple delhezi bichirs, a rocket gar, two fat sleeper gobies, and a tiger datnoid. All are active and besides the gobies are out all the time but tend to stay at the bottom. Only fish that really uses the upper part of the tank is the rocket gar and the datnoid. I am looking for a fish that will spend most of its time in the middle to upper parts of the tank. My tank is currently a 90 gallon but I can move up to a 125 when needed. Any ideas?