problem(?) with tang

[jacksonpt]

I bought what was sold to me as a yellow tang, but I'm pretty sure is actually a mimic tang. Anyways, when I got it, it was bright yellow, swam well, ate well, etc. All was good. About a week later, I noticed that it's color wasn't as good... it looked like it was starting to turn black. It's been that way for about 3-4 weeks now. Looks like it's covered in ash. The black is very dark at the mouth and gill covers. All water parameters are perfect, he still eats and swims fine. Nothing has changed in the tank or with the tang's habits or manerisms... he just looks like he's covered with ash. FWIW, he won't eat seaweed selects, only general flake food, but he's constantly picking at the rocks and glass. There are still patches of algae on the rocks. Could it be a nutrition issue... i.e. not enough of some vitamin is affecting his color?

 

[jacksonpt]

ah, that sheds some light on things, thanks. I had a hard time finding any real info on mimic tangs, but that site says they change color as they get older... go from bright yellows to drab blues. Not real excited about the drab blues, but at least I know what's going on. The pic looks very similar to mine, but mine dark on the whole body.
Thanks again.

 

[von_rahvin]

altantic tangs also change colour when they are put under stress. mimcs do it as well. major differene beyond the lakcing of a tail barb is the mimic has a more "smashed in" face, while the yellow tang has the snout