Rose line shark issue

[Johnnoe]

I have a 50 gallon planted tank all the peramiters seem to be good to go (use API liquid test). The issue I am having is out of no where my roseline that I have had for a while formed a spot above his eye that looks like he has been attacked. I am new to the hobby and simply do not know how to diagnose the issue as being illness or an attack from another fish. I have included pictures as best as I could.

 

[Mark Z.]

Do you have any larger aggressive fish in the tank that could have taken a bite at him?

 

[Johnnoe]

I have 3 New Guinea reds 1 golden gourami 9 golden barbs 2 plecos but he is by far larger than all of the other fish the only fish bigger than him is another roseline

 

[Johnnoe]

oh and two small flying fox