NTHA, here is a thread I started on fingerling BG, GSF and RES with pictures. I am no fish expert, so if some of the experts have opinions on the pedigree I welcome it. Very possible I could be mistaken.
But the pictures show small fish side by side, which is very helpful to distinguish some of the subtle differences Bill Cody talks about.
As the fish grow a little larger, ID becomes much easier. I have been trying to ID fish only going on 4 years now and I know in the beginning it was very difficult for me. I posted these pictures for people in the same situation I was back then.
Fingerling BG, RES,GSF and some hybrids identification 
