Hybridization and Replacement of Roanoke Bass with Invasive Rock Bass in Virginia: A Genetic Analysis of the Problem

The Roanoke bass is a sport fish endemic to several drainages in Virginia and North Carolina.  Virginia populations are threatened by competition and introgressive hybridization with rock bass, an invasive congener introduced to many waterways between the 1890s and 1950s.  The current status of this invasion and its impacts on Roanoke bass populations are unknown.  Eleven microsatellite markers were developed to discriminate between Roanoke bass, rock bass, and their hybrids, and in doing so to assess the current distribution of Roanoke bass in Virginia.  The panel of markers provided a high degree of resolution, allowing us to discern F1 hybrids and backcrossed individuals.  Our results suggest a mosaic of invasion, displacement, and introgression patterns across the range of Roanoke bass in Virginia.  Roanoke bass persist in 4 of the 8 watersheds examined, but have been mostly to completely replaced by Rock bass in 3 others. In the Pigg watershed, an ongoing invasion is apparent: rock bass and hybrids were distributed throughout this system.  All extant Roanoke bass populations are vulnerable to future invasion.  This highlights the importance of educational campaigns that discourage anglers from transplanting rock bass to new waterways.