What did you catch that RES on?
How do you normally fish for them and how IYO do they bite relative to BG?
I caught this one on a small dart head jig with a black soft plastic stick thing about 3/4" long. I've caught quite a few on a bead-head trout fly.
Earthworms/nightcrawlers work pretty good too.
I just drop the jig into the water off the edge of the dock, let it hit bottom, pick it up and wiggle it around real slow.
They usually smack it with a purpose. They will swallow a live worm really fast so I don't use those much in my pond.
In other waters, if I'm catching to keep, a worm under a slip float is hard to beat.
BG seem to be a bit more aggressive than RES. If they're schooled up together you'll usually have to catch a bunch of BG to catch a few RES.
That could be simply because BG tend to vastly outnumber RES in waters where they coexist.
I haven't tried the fly rod on them yet, but I do intend to give that a shot in the future.