Hey I was looking online for you and found this, it is kind of similar to your situation:
QUESTION
"i have a silver arowana at home. just recently, i transfer it to a larger tank. during the process, it jump out of my hand and fall onto the floor. when i already transfer it to another tank, i discovered that one of its scales on its body had gone off. can it be regrowth by itself? or i have to do something about it? it now looks like a patch on its bofy without scales. thanks."
ANS
In a healthy aquarium, fishes have little difficulty in regrowing scales. Having said that, the tussle the arrowana went through may have done damage to the fish beyond the scale loss. Damage to any venerable areas, like the eyes and gills, could lead to more serious problems. The most we might do is a prophylactic treatment of antibiotics to reduce the chances of secondary infection.
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That was from aquariumpros. Maybe you should think about the prophylactic meds to stop the damage. I have never seen it before, I wish I could be of more help. Ill keep researching.