Yes that is an alligator gar that you have. The only true way to identify an alligator gar from all the others is that an alligator gar has two rows of teeth in the upper jaw, all other gars have one row. I have two right now at 14" and I got them about the same size as the one you have. Good rule of thumb- if it will fit in their mouth and they could swallow it, then they will. Mine are about one year old and I kept them from growing too fast by not feeding them everyday. They don't have the best eyesight and sometimes they will strike at another fish that flashes by them, but other than that they have been peacefull with my other fish. I have a 6" nile perch with them and they don't even bother him. I hand feed mine thawed frozen smelt and shrimp. They are really cool to watch eat. Congrats on your new one, good luck.