I'm pretty sure those are repeated slash marks from your ATF. In my experience I've seen the same type of injuries inflicted by my pack of ATF. It doesn't look like the atf bite of you think it's the result of one or two goes. It's actually an accumulation of aggressive fly bys. I think your tarpon is a bit too small to fend for itself in that tank. Underclassed in everyway possible. My advice is take out the tarpon.. Also in my past experience, hoplias really didn't get along with specifically goonch for some reason. Almost suffered a tailless goonch as well but traded before it suffered the same fate.