Take a look at this one. This is supposed to be a RES fingerling in a pond where all that was stocked were RES as far as sunfish species go. But I have trapped at least one GSF fingerling in this pond recently. So I have invaders (possibly swimming up the overflow pipe during a high water event).
Mine looks more like a GRES than yours. I think yours is pure RES. Look how long the pectoral fin is on yours.
