Looks like an old scar or natural coloration as mentioned above. Either way there's nothing to do. How long have you had the fish and when did you first notice it?
Sent from my mind to my fingers to my phone to the MFK servers to you
thanks
have him about 4 months now. didnt notice it until about a month ago. like i said though hasnt really got worse or better. treated with a course of melafix, but didnt really seem to do anything for the area.
Sounds like he either scratched himself on something or you just didn't notice he already had it. If it was a scratch it MIGHT color back up but I wouldn't count on it. Either way he's still a nice looking fish.
Sent from my mind to my fingers to my phone to the MFK servers to you