Genetic change and ancestry of introduced populations of silver carp as revealed by mitochondrial DNA

Silver carp Hypophthalmichthys molitrix, is native to China but has been introduced widely for aquaculture and water quality control.  We evaluated the Asian sources of two introduced populations and determined their rate of genetic divergence.  We sampled 241 silver carp from river systems where they are native (Yangtze, Pearl and Amur Rivers in China) and introduced (the Mississippi River basin [MRB] in North America and the Danube River in Hungary). We analyzed two mitochondrial markers: the control region (D-loop) and the cytochrome oxidase subunit I (COI) gene.  We obtained 72 haplotypes. All haplotypes of the Yangtze carp were found in other populations, which is consistent with geological and fossil evidence that the Yangtze River is the evolutionary source of silver carp.  Within less than half a century, genetic differentiation of silver carp in introduced populations was limited but detectable. Both sequence analysis and examination of haplotype distribution indicate that the Danube population is most closely related to the Yangtze and Pearl river populations, but the Mississippi River population is most closely related to the Amur River population.  This more northerly ancestry of silver carp may be important in understanding the current and future range of silver carp in North America.