Quantifying the effects of introduced Bighead Carp (Cyprinidae; Aristichthys nobilis ) stocking on dominant fish species in the Ulungur Lake, China

Nonnative fish species introduced into new areas, especially when they develop into large populations, pose a threat to wild fauna. We used stable isotope analysis to quantify the ecological effects of introduced Bighead Carp ( Aristichthys nobilis ) stocking in Ulungur Lake on the basal food source composition, isotopic niche width and niche overlap of four dominant fish species including Bighead Carp, Pond Smelt ( Hypomesus olidus ), Common Bream ( Abramis brama ) and Common Carp ( Cyprinus Carpio ). Following Bighead Carp stocking, proportional contributions of phytoplankton to fishes significantly decreased for the other fishes ( P < 0.05), and the contributions of particulate organic matter to the fishes significantly increased ( P < 0.05) except for Common Bream . In addition, the total isotopic niche width of fishes increased from 12.01 to 13.06 and isotopic niche overlap between fishes increased from 22.75% to 42.50% following stocking; this change was particularly apparent in the large changes in the isotopic niche overlap between Common Bream and Bighead Carp (from 67 to 95%) and between Common Bream and Pond Smelt (from 65 to 100%), followed by that between Bighead Carp and Pond Smelt (from 0 to 90%). Furthermore, the obvious increase in isotopic niche overlap may be the reason for the reduced growth observed in Bighead Carp and in Pond Smelt. These findings highlighted that Bighead Carp stocking changed the availability of basal food sources for other sympatric fishes and increased the potential for interspecific competition among fishes. Overall, our study suggested the introduced Bighead Carp stocking had undesirable effects on fish community in Ulungur Lake.