I will give you the benefit of the doubt.
What you have appears to be a Hi-Back Red-Tailed Golden Arowana (and a beautiful one at that).
That planted tank is awesome. And you are on the right track in keeping him in the tank alone. You can have some suitable tankmates (just check the threads here for that).
You can keep him in a 280g tank (or bigger); he'll be perfectly happy.
I would feed him fresh shrimp or prawn (if they are available out there), maybe 3 to 4 pieces cut up into smaller segments once or twice a day, and maybe some live feed once in a while (once a week or once every two weeks).
Good luck with that one -- it's a beauty!