I observed several of these fish, 2-3 inches long, in a shallow section of the Pecos River. They seemed to approach each other with the blue/green color on the back being displayed.
Live Oak Creek
Adult under a rock. With Bill Holmstrom. Imaged only. GTS 2550.
Dolan Falls Preserve is owned by The Nature Conservancy and is not open to the public. Access is through special permission only. The preserve is adjacent to Devil's River State Natural Area, which is open to the public on a restricted schedule.