To understand the turnover and fractionation characteristics of carbon and nitrogen stable isotopes in Procambarus clarkii,the turnover half-life of carbon and nitrogen stable isotopes and the muscle tissue discrimina-tion factor of two different sizes of P.clarkii(juvenile and adult)under different feeding conditions(feed and fish mince)were investigated in an indoor controlled experiment.The results showed that there were no significant differences in the growth coefficients between P.clarkii(juvenile)fed with feed(0.008 5±0.000 7)d-1 and those fed with fish mince(0.007 9±0.001 2)d-1.The differences in the growth coefficients between P.clarkii(adult)fed with feed(0.001 3±0.000 1)d-1 and those fed with fish mince(0.000 9±0.000 4)d-1 were no significant too.The relative growth rate of P.clarkii(juvenile)group(1.60,1.57)was higher than that of P.clarkii(adult)(1.08,1.05),while the relative growth rates between the feed and fish mince groups showed no significant differences.Compared to the feed group,the fish mince group exhibited a significant difference in the carbon sta-ble isotope ratio(δ13C)of the original crayfish species on the 7 d,which stabilized from 28 to 56 d.The carbon stable isotope ratio of P.clarkii(adult)group showed significant differences on the 14 d,also stabilizing from 28 to 56 d.Moreover,the nitrogen stable isotope ratios(815N)of both P.clarkii(juvenile and adult)displayed sig-nificant differences on the 14th day,subsequently stabilizing from 28 to 56 d.The turnover rate of stable carbon isotopes in P.clarkii(juvenile)(0.0208±0.004 0)d-1 was higher than that in P.clarkii(adult)(0.018 4±0.002 0)d-1.The carbon stable isotope discrimination factor of P.clarkii(juvenile and adult)were 0.89‰±0.15‰ and 1.06‰±0.16‰,respectively.Similarly,the nitrogen stable isotope discrimination factor of P.clarkii(juvenile and adult)were 3.42‰±0.08‰and 3.63‰±0.13‰,respectively.It is worth noting that the carbon and nitrogen stable isotope discrimination factor of P.clarkii(juvenile)were smaller than P.clarkii(adult).These results provide fundamental parameters for the application of carbon and nitrogen stable isotope techniques,thereby enhancing the accuracy of food source analysis in P.clarkii.
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