I have two severums in a 55 gallon but they won't likely be in there much longer. They aren't fully mature yet. I don't think mature ones would do well in a 55. I was planning on getting a larger tank this year but my severums seem to be pairing up and so I may be buying something bigger much sooner then planned. Anyway for now they are okay and you could definitely do it with small severums that aren't mature but you'd have to plan for something bigger down the line. Mine are in a community tank with rams, a blood red parrot, and a firemouth. They all get along fine. I also have some cories and a raphael catfish in there, no problems. However there used to be some otos in there and I'm positive my larger severum ate them. I have never seen him bother anyone else. I wouldn't add anything small to the tank now for fear my male would eat them. Most of the fish that are in the tank now were added within weeks of each other and all the fish were small so they have grown together. I think if I added something new at this point the firemouth and larger severum would pick on it.