Stable Isotope Analyses in Otoliths of Silver Carp: a Pilot Study in Identification of Natal Sources and Stock Differences

Silver carp, Hypophthalmichthys molitrix (Cuvier et Valenciennes), is one of the major species in China for fishing and culture. The Yangtze River and associated waterbodies are important home to silver carp. However, genetic analysis indicated that there were marked distinctions between one population in Ganjiang River (a large stream drained into Yangtze River through Poyang Lake) and the other in Yangtze River, and the population in Poyang Lake belongs to Ganjiang River rather than Yangtze River. To protect and manage the fishery resources, these genetic results need to be validated for a better understanding on the population structure of silver carp. In this study, we collected 135 otoliths of juvenile silver carp from both rivers and Poyang Lake, and analyzed for stable oxygen and carbon isotope ratios (δ¹⁸O and δ¹³C). By comparing the isotopic fingerprints in otoliths we expected to obtain valuable chemical information about the natal sources of silver carp and verify the population differentiation between Ganjiang River and Yangtze River. The preliminary results indicated that, as reported previously, the isotopic signatures of otoliths can be effectively used in study of natal sources and early life history of silver carp stocks and environmental changes. More analysis is underway.