How do I tell if my Mandarin is getting enough to eat?

[Kit with Cat]

I've been told Mandarin dragonets can devastate an entire population of pods in a few days. How do I know if this has happened? I have a refugium as well, but I don't know if that will be enough to feed him? Also, I've been looking for pictures on the net of how a well fed Mandarin should look like and what a starving Mandarin looks like, but I can't find any. Any help would be awesome...thanks so much!
Kit