Carnivorous Top Dwellers

Question

This is the Pacu  

This is the Snakehead,   I have a Snakehead and a Pacu.I know the combo sucks but,the both don't compete with or attack each other.Occasionally the Snakehead comes up for air and goes back down into its cave and the Pacu is always at the bottom quarter water level.They both eat feeder fishes very well.The feeder fishes eats tiny pellets which I only feed cause my Pacu eats it as well.I have a plant, which the Pacu amazingly does not nibble on.And now I want a predator that swims at the top.Something big enough that the Snakehead doesn't attack,and something small enough to share feeder fishes with the other two predators.An active swimmer,not very common,that blends in with the colour scheme(Red Belly Pacu,Bronze Snakehead Murrel with dark zebra-like stripes,Black background glass tank,Green Plant).By the way, the Snakehead,Pacu and the Plant have been together with the same pump set up for almost two months now,no injuries,stable water conditions,no infections and most importantly visible growth.I replace one third water weekly.Please help me choose a fish.

Answer
I am jealous of your snakehead. They're some of my favorites but I've never been able to get one since they're illegal in the states. Anyways...
Those java ferns are great too because they're easy and NOTHING eats them. They're one of two plant species I regularly keep.

If the tank is large enough (probably 700L+), I think any arowana would be awesome. They fit your description perfectly, they just get big.
I've had a silver arowana for years now, it's about 0.5 meter long, active, eats anything, and absolutely beautiful.

In this tank, maybe a flagtail would be a good fit. Pretty, and very active. Diet may need some special attention though.

Hope this helps a little. You have tons of options, those are just my personal choices. If you have other ideas, feel free to run them by me.