How do tell if Medaka fry are well fed?

I think I'm suffering from a lack of confidence brought on by a lack of experience raising fry. How do you tell if they are well fed? I suspect that there may be a lot of natural food. That's why when I add more they don't seem hungry.
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Got no experience with rice fish at all, but you're correct in the white bit above the tail being the stomach and looks to be fairly full in most of them. By the looks of the tank there plenty of food in there for them to eat plus all those other goodies your giving them.