It's difficult to see whether it's a scrape or an infection...looks more like a physical injury to me. Either way the most important thing to do is make sure the tank is clean, that's the best way to avoid infections. You can add some Indian Almond Leaves to the tank, as they help reduce stress and have mild anti-bacterial properties. Don't medicate unless you see signs of infection, as dosing a healthy fish could potentially be dangerous. And I would strongly advise against using melafix (or bettafix, for that matter) - both of these medications can damage the fish's labyrinth organ and potentially be lethal. There are far safer alternatives.
