Convict Cichlid has a weird scratch?

So I have been slowly adding fish to my cichlid's aquarium without much issue surprisingly. Well today I added one fish and even though a fight hasn't broken out my convict has been chasing this fish all day. Still no biting just chasing. Well she was fine when I left to pick my fiance' up from work and when I got home I saw that she has a thin black line going down her back like she got a scratch or something. Is there anything I should be doing about it or could it possibly be a symptom of something? Maybe a fight broke out when I wasn't looking?