Black angels mark easier than any fish I've ever seen. Blacks pairing up look like a train wreck, white spots & gashes everywhere. If there was any aggression, as there probably was seeing as part of a fin is missing, white marks are to be expected.
The red gill could be from aggression, or it could be a short gill plate. If the fish has a normal respiration rate, & it's only one gill, I wouldn't be worried. If it's battle damage, the gill plate will probably grow back, if it's a short gill plate, which is a birth defect, it won't.
Water changes every other day, & a little melafix will help the damage. Often just the water changes is enough. Try to remove anything from the tank that is even close to sharp or abrasive, or other marks will show up. I've had blacks get spooked, zip behind a piece of driftwood, & come out sideswiped. They heal up in a few days, it looks a lot worse than it is.