Doesn't look like duck lips. Obviously you did a head count on your grow outs? My Jd ate 2" tiger barbs like it was nothing at 4" but several didn't go down so easy, and usually it was his stomach that told the tale.
Injury or rock would be my guess. monitor him and keep the water quality high and stress free. Best of luck. keep us updated as to any change in behavior. He looks like a beautiful fish