Stable isotope analyses in otoliths of silver carp: a pilot study in identification of natal sources and stock differences

Abstract

Silver carp, Hypophthalmichthys molitrix, is one of the four major fishes in China for fishing and aquaculture. The Yangtze River and associated waterbodies are important home to silver carp. In this study, we collected 135 otoliths of juvenile silver carp from the two rivers and the Poyang Lake, and analyzed for stable oxygen and carbon isotope ratios (δ18O and δ13C). The isotopic data and correlation of δ18O versus δ13C showed a clear separation and significant differences (p < 0.001 for both δ13C and δ18O) between otoliths from the Ganjiang River and the Yangtze River at δ18O values around −10‰. The Poyang Lake samples were overlapped with those of the Ganjiang River, but distinctly different from the Yangtze River samples. These isotopic signatures agree well with the previous genetic investigation results that there are marked distinctions between one population in the Ganjiang River and the other in the Yangtze River, and the Poyang Lake population belongs to the Ganjiang River rather than to the Yangtze River. Thus we concluded that stable isotope analyses of otoliths can be effectively used to study natal sources and stock differences of silver carp.