I have had these clownfish since November 2016 and I have never noticed this until the other day. I also have recently noticed that my Duncan had been closing up so I have to wonder if the clowns are rubbing up against at times when I am not around so that is where the black spots are coming from? They are eating fine and look healthy and swimming around. The black clowns do not have any markings whatsoever so it leads me to believe that it is not black ich. Would like some help on the matter and advice.
Common in clownfish, this appears as brown spots or ovals where a stinging coral or nem as come into contact with the fish’s skin. Typically nothing needs to be done to cure this as the clown becomes accustomed to it’s new host’s sting. This can occur with other fish, but again no action needs to be taken. It will heal up on it’s own.