Mitochondrial DNA diversity, population structure, and conservation genetics of four native carps within the Yangtze River, China

Silver carp (Hypophthalmichthys molitrix), grass carp (Ctenopharyngodon piceus), bighead carp (Aristichthys nobilis), and black carp(Mylopharyngodon piceus) rank first, second, fourth, and seventh in world fish production. In China, the Yangtze River harbours the most important natural populations of these species. We performed a polymerase chain reaction - restriction fragment length poymorphism analysis on 365 juvenile fish representing three nursery grounds to provide a first assessment of the mitochondrial DNA diversity in these species and test the hypothesis that they are composed of more than one genetic stock. The mitochondrial DNA diversity was high in silver, bighead, and black carp, and much less in grass carp. Analysis of heterogeneity of genotype frequency, fixation indices, intersite molecular variance, and localization indices indicated that juvenile silver, bighead, and black carp from different nursery areas belong to genetically distinct populations. These results suggest that their population structure may be determined by the number of environmental settings that permit closure of their life cycle. They also imply that carp from the Yangtze River cannot be managed as a single unit and that human disturbance through exploitation and habitat modifications, in particular the construction of the Three Gorges Dam, will have differential impacts on fish abundance for different parts of the river.