Need an ID please.

[jpruitt]

This tang has been in my tank for over a year now. Eats like a horse and was properly qt'd before he entered my display. Tank is a 190 gallon.

Parameters are as follows.
Alk 8.6
Calcium 440
Mag 1380
Temp stay between 78.8 and 78.9 very stable.
All other parameters are within normal levels.

No new additions to the tank in over a month which was qt'd as well. Never had ich in the display.

Any opinions would be appreciated on what this is. Reference the pic it is the black spot on each side on the tang. Literally showed up over night. Thanks.

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[Deinonych]

Looks like it could be a bite mark. What are the other inhabitants of the tank?

 

[ThRoewer]

Are those spots raised or smooth?
If slightly raised and the edge is rather sharp, it could be a flatworm.
If smooth it could be a discoloration due to a coral burn or sting.