Ned -
I was in your store the other day and somebody (not sure if was you or another of the guys) said they had trouble sexing Mandarins, which resulted in some violence. Just an FYI, it's pretty easy:
The males are somewhat larger than the females, have longer fins, and the first ray of the dorsal fin is about twice as long as the female's.
I forgot this at the time, but now that I think about it, I do recall seeing females and noticing that the dorsal fin was dramatically smaller than the males. The females do not have the "spike" that extends from the fin outwards.
Just wanted to pass it along.