Is it the gills themselves.....The gills should look red in color-this is a sign of proper oxygenated blood circulation, however, they shouldn't look angry red and inflamed or pinkish, pale, brown, blue, purple.
What are you doing for the buoyancy problem, sometimes it can be due to genetic, labyrinth organ, poor care/feeding at the fish farm before he every left the fish farm. Sadly, that can end up being a long term problem and symptom may even come and go as he matures, with stress, eating...etc....
You may need to use low dose Epsom salt 1tsp/gal long term as well as retaining high levels of heat/humidity over the water.
Can you complete the sticky info sheet found at the top of this section and a pic of the gills.