Population Differentiations of Silver Carp in the Yangtze River,True Or False？and Why If True？

Silver carp, Hypophthalmichthys molitrix is one of the major capture and culture fishes in China. The Yangtze River and the adjacent lakes, such as Dongting Lake and Poyang Lake are main home to silver carp. However, genetic analysis indicated that there were remarked distinctions in genetic structures between two stocks in Ganjiang River and Yangtze River and between two populations in upper reach and middle reach of Yangtze River as well. Analysis of oxygen and carbon stable isotopes in otoliths in combination with analysis of genetic structures using microsatellite maker were adopted to address the issues. Two potential causes resulting in population differentiation of silver carp in the Yangtze River watershed (physical barrier and instinctive homing behavior to natal sites) were hypothesized and verified. The first-step study demonstrated that the isotopic signatures (δ¹⁸O and δ¹³C) in otoliths can be effectively used to study natal sources and stock differences of silver carp. In-depth genetic analysis and comprehensive stable isotope analysis in otoliths of silver carp samples from different waterbodies (the Yangtze River, Ganjiang River and Poyang Lake) and age groups (young, subadult and adult) are underway. Some latest results such as genetic differentiation of silver carp will be presented.