suggestions on new fish purchase

[shadyfish]

Hey everyone ok so I have a 55 gal with a red tailed barracuda a tiger dat and a Senegal bichir my family wants to add another fish but after two fish returns due to aggression I'm hesitant to drop another gilled friend into the "thunderdome" can anyone give me a suggestion as to what I can put into the tank keep in mind this is strictly a predator tank and any fish need to be able to hold their own I recently had to move my emerald cory to my feeder qt because he was being harrased by the dat thanks this forum is the best BTW I've gained so much info from here that I would have learned the hard way

 

[Jason7894561230]

A group of tiger barbs would work in your tank. They are agressive but like a group of 6