Firefish issue

[Beano1169]

My firefish seems to have hurt his top dorsal fin he is a juvi so he isnt very large about 1.75"- 2" but I see that his feen looks a bit ripped yet a slim almost see through bone is still at the top passed the rip on the skins surface. Is this fin-rot? or did he just smash into a rock and pull some skin off? He is behaving normal swimming around, hiding in his corner. any suggestions?