Abstract
The Chesapeake logperch, Percina bimaculata (Halderman) has a disjunct distribution when compared to other species in the subgenus Percina. Members of this subgenus in Pennsylvania include Percina caprodes caprodes (Rafinesque), Percina caprodes semifasciata (DeKay), and P. bimaculata. Historically the Chesapeake logperch was known only from the Susquehanna River and Potomac River basins. Its range is now restricted to the Susquehanna River below Holtwood Dam and upper Chesapeake Bay. It has been extirpated from the Potomac River and the type locality near Columbia, PA. Attempts are being made to reintroduce it into tributaries of the Susquehanna River near Columbia, PA. We postulate that P. bimaculata diverged from a population of Percina caprodes semifasciata. A naked nape and the fact that both of these species do not occur above the fall line in Pennsylvania support such a relationship.