I believe it is a green sunfish cross with a bluegill, but the body symetry doesn't quite look right for those hybrids. Most gsf X bg hybrids have wider bodies and more bluegill characteristics than your fish. Yet yours doesn't quite look like a pure greenie, either.
Thanks for this information. I caught this fish in a tidal cypress swamp in Maryland. I had no idea that green sunfish were even here. I typically catch bluegill and pumpkinseed together but have never caught other species of sunfish. The black water gives most fish a darker than normal color.
As soon as I saw the bright fins, I thought I had caught a green sunfish. After reviewing pics online and my field guide, I realized the coloration is different and the mouth of this fish is definitely unlike a bluegill, but it seemed to be too small to be a green sunfish.