Hi hhender and welcome to the forum. I'm sorry about your guy. From the pics, I don't see any sign of fin rot but it is possible that he has a bit of ammonia/nitrate poisoning that could cause him to breathe hard. There's also a possibility that he has gill flukes too. Either way, I would suggest treating him with 1 tsp of AQ salt per gallon and frequent water changes (25-50% a day). If you have live plants in your main tank, I would suggest treating him in a smaller hospital tank; most plants do not tolerate salt.
If the AQ salt treatment for 10 days doesn't help, then your next step might be to find a medication called methylene blue. I've read in my research that this can be very helpful to aid in ammonia/nitrate poisoning.
Good luck and keep us updated.