Bala shark missing scales

[Manbot]

Hey I've recently noticed that one of my Bala shark is missing scales- the other one is fine- is this disease? Or Is hiring himself on the ornament/driftwood?

 

[HUKIT]

Bala's are skittish fish when not housed properly, they are social schooling fish that are spooked easily when not stocked with number of at least three. So my guess would be a injury, keep the water conditions pristine and monitor the area.