Dark spot on Midas Blenny

Hello,

I was wondering if anybody can help identify what this may be. I'm not sure exactly when it happened (it may been gradual) but my Midas Blenny started to have a dark spot on one side only (photo attached). It seems to be fine.. swims around normally and seems to have a healthy appetite. Wondering if I should be concerned.. or did it just hit itself on a rock ?

strange looking spot. i dont think you can do anything about it. if he is eatting i am thinking you will just have to take a watch and wait aproach. is possible he has some kind of internal parasite but i would think you would see it on both sides of fish. those guys arnt exactly thick bodied.