Spots above Yellow Tang's Eyes

[WiscSea]

My yellow tang has some faint dark spots above each of his eyes. His behavior and color are ok. Although his white line might be a little more pronounced.

Any ideas what this may be?

 

[kraze3]

Check these sites

http://www.petsforum.com/personal/trevor-jones/blackich.html

http://www.reefcentral.com/forums/showthread.php?s=&threadid=466874