Is tis normal for male ray？

Hi to all Shifu， got a qus to ask is tis normal coz most of my male ray have it？
They have some skin peel off at the egde of his gun (bird) 。 Thank u

Thank all Shifu aft
==comments==
my female seems to have it too。

hope we gets reply from the gurus here。。。！AquariumIs tis normal for male ray？