A 55 isn't large enough to keep Heterotilapia buttikoferi, even as a single. Recommended size is at least 75. And this is a highly aggressive species, which makes for an interesting "wetpet", but not good with others, even of their own kind, without a lot more space.
"Tilapia" raised as food are often hybrids of various large, fast growing Oreochromis species, usually aureus and/or niloticus. These fish will get much too large for a 55. The first is used because it tends to be heavy for its size, while the second gets much larger, over a foot and a half in length. They are also voracious feeders and turn poor feed into usable protein.
As noted, there are states that list them as game fish due to large feral populations, and keeping certain game fish usually requires permits. However, because they are commercially raised as food fish, I'm not sure such rules would apply to "Tilapia".
There are more interesting - and more colorful - species of actual Tilapia, some practically dwarf compared to the above.