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This paper studied the sources of food and the trophic levels of silver and bighead carps using stable isotopes (δ 13 C and δ 15 N) analysis in Lake Qiandao and Lake Taihu. The δ 13 C values of POM and phytoplankton indicated that Particulate Organic Matter (POM) is of terrestrial origin in LQ and phytoplankton origin in LT. The different signature of δ 15 N of phytoplankton and POM also showed the different extent of anthropogenic impacts on the two lakes, with higher impacts in LT than in LQ. In LQ the trophic levels of silver and bighead carps were significantly different (2.48 ± 0.19 and 2.66 ± 0.19, respectively), while in LT the difference was not significant (2.15 ± 1.54 and 2.36 ± 0.38, respectively). Using a mixing model, we found that silver and bighead carps consumed a major proportion on phytoplankton and/or POM in both lakes with higher contribution of phytoplankton in more eutrophic lake. Silver and bighead carps had clear differentiation in food resources with silver carp more on POM and bighead more on zooplankton in deep and mesotrophic lakes. Contrary to this, both carps fed primarily on phytoplankton (and POM) and may have more niche overlaps in shallow and eutrophic lakes. [ABSTRACT FROM AUTHOR]

Coilia nasus is widely distributed along the coast, and rivers and lakes that connect with the ocean in China. It is a diadromous fish but has residential populations in the middle and lower reach of the Yangtze River and its associated lakes such as Lake Taihu. These ecologically differentiated diadromous and residential populations are difficult to identify and separate, even with current molecular screening methods such as applying the mtDNA markers. The objective of the present study was to screen these populations by the means of the whole body elemental fingerprint analysis (EFA). Our results showed that the diadromous population had significantly lower concentrations of Al, B, Ca, Cr, Fe, K, Mg, Mn, P, S, and Zn, and significantly higher As than the residential populations. The spawners had lower concentrations of B, Cr, P, and S before laying eggs than after laying eggs. Advanced statistical models detected distinct spatial patterns between the diadromous and residential populations, and between groups before and after spawning. The current study showed that the whole body EFA can clearly distinguish C. nasus populations in the Yangtze River Basin and thus proved to be useful and may substitute the elemental fingerprint of fish otolith in future fish ecological studies that need to identify different populations. [ABSTRACT FROM AUTHOR]