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Intra-lake stable isotope ratio variation in naked carp Gymnocypris przewalskii with different body size in Qinghai Lake, China

Yueqin Yanga, Shouchun Lib and Xianfeng Yib

Stable carbon and nitrogen isotopes were measured in biota collected from Qinghai Lake (China) to describe trophic relationships and diet of naked carp (Gymnocypris przewalskii). The results showed that naked carp were at the apex of the food web with dissolved organic matter (DOM) forming the food web base. δ¹³C ranged from -26‰ (DOM) to -18‰ (submerged macrophytes) with invertebrates ranging between -23‰ (benthos) and -20‰ (zooplankton). δ¹³C values of naked carp spanned the entire range of other taxa, from -25.7 ‰ to -18.1 ‰, with larger fish having higher δ¹³C values. However, δ¹⁵N values of naked carp showed relatively little variation, ranging from 11.3 ‰ to 14.4 ‰. Body size was correlated with δ¹³C and δ¹⁵N values, indicating naked carp elevate their trophic position as they mature. Naked carp in Qinghai Lake have a broad diet associated with opportunistic feeding, although larger individuals consume larger preys which have higher trophic positions, including its own young. Opportunistic feeding, including cannibalism, may reflect the response of this top predator to deteriorating ecological conditions in Qinghai Lake. This new knowledge of the feeding behavior and trophic ecology of naked carp can help us manage this potentially endangered species and provide insight into better management and improvement of the current fate of the species.