Look like Florida gar. Gets about 18-24 inches. Not sure about growth rate but someone here can inform us. Surely 55g will eventually not suffice. But nice looking gar.
He does not swim much when I'm looking at him. He just stares back at me. He does poop daily. He is currently in a small tank. When I'm vacuuming the tank, he does swim very fast. I wonder if he is lazy.
Nothing really that you can do. If he has movement in it back fins it should recover mostly. Will always show some evidence of having broken it's back though.
Gars don't swim fast like other fish. My gar completely healed from a broken back overnight without any evidence of it later on. Floridas can grow an inch per week depending on what they are fed, and they usually slow down at 14-16 inches, possibly even 12.