I can't tell you for sure, but it looks exactly like what I stocked as RES right down to the reddish tint of the lower fins. As they get bigger, will be easier to tell.
I personally do not see any GSF signs in that fish. The mouth size would be the only thing that possibly might be. No green bars on the cheeks, the orange tab is a dot (which is normal on small RES) rather than a translucent border that wraps around the tab (like on a GSF), No blue-green flecks in the coloration, no tipping of the fins of yellow.
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.
Thanks guys, that's what I was leaning towards. I originally stocked RES in the fall of 2014, and have yet to catch any. Good to see signs of their presence.
Steve try fishing with a 1/32 oz jighead and crawler piece on or very near the bottom. RES are more benthic oriented than many of their Lepomis cousins and will be looking down for forage like crustaceans. Also a tube jig or jig/crawler drifted under a float so it's just kissing bottom has performed for me historically.
Many men go fishing all of their lives without knowing that it is not fish they are after. ~ Henry David Thoreau