the filaments on the gill stems are very delicate and because the veins are close to the surface very easy to catch and bleed, this is more noticeable on albinos/goldens/lucies then on mels/wild, keep an eye to make sure that the bleeding has stopped, because of how small the area is it will be difficult to see if it it is healing.
keep the water cold (shouldn't need fridging) and the water parameters/chemistry good to allow for optimum healing conditions.