Hard to say but looks like a twig stuck in it s face. Blood wouldn’t coagulate in that shape. Crazy looking.
SoI thought it was a stick stuck into its face too. Never seen anything like this before. Is it possibly some kind of parasite? I doubt blood would form that shape but I dont really know, How is the fish acting, is he eating and acting normally?
If you could get some real close up pictures it may help someone identify what it is. Maybe even take the fish out of the water to get a good look at it and snap some pictures at the same time nice and close.
That would make sense it being from a pleco.Looks like it came off the pleco. Is he missing any parts? (Pleco) pics?
My pleco and male green terror used to fight a lot. I moved the pleco because it was so upsetting to see how violently they would get into it.