Cleaner Shrimp belly?

[Gowanlock]

One of my two cleaner shrimps has a weird black mark on its belly... See pics. What is it? Are they mating? Is it dying?

 

[HumbleFish]

I've seen that before... don't think it's anything to worry about. Might wanna also post this in the "Reef Discussion" forum though.

 

[Gowanlock]

Thanks Humblefish! Will do!

 

[billsreef]

[moved]...

 

[Betta132]

Wait and see if it goes away when he sheds. Not sure what that is, but no, they are not mating. Could be some sort of odd algae or just a weird coloration.