Hybridization Between Largemouth Bass and Florida Bass in the Devils River, Texas: Influence of Reservoir Stocking On Upstream Populations

Florida bass Micropterus floridanus have been stocked in reservoirs across much of the range of largemouth bass Micropterus salmoides.  However, little is known of the effects of stocking fish in reservoirs on upstream populations.  We examined hybridization between native largemouth bass and introduced Florida bass in the Devils River, Texas, upstream of Amistad International Reservoir using a panel of six diagnostic microsatellite loci.  Hybrids comprised the majority of the population in the Devils River both above and below Dolan Falls.  However, the proportion of hybrids was greatest below Dollan Falls.  Among hybrids, mean proportion of observed alleles derived from Florida bass was 0.46 and ranged from 0.08 to 0.92.  These results indicate that stocking of fish in reservoirs can have pronounced effects on upstream populations and might present a threat to the conservation of native populations.