Hi,
Thats a growth plate you are seeing.. if the fish were darker colored you would probably see what looks a small gash on the gill plate. Its typically from power feeding high protein foods and and/ or lack of proper minerals in the diet or water. Do you have soft water? These are basically stretch marks where the fish is putting on muscle and tissue faster than the skeletal system can keep up with.
Solutions.. add more minerals to your water.. or add more minerals to your beefheart mix. Changing more water may help as well.
In your case these will probably not have scars that are visible because they are light colored if you fix their diet
If they were darker base colors scarring can happen. I've seen this first hand in my tanks years ago when powerfeeding beefheart mix..