Determination of the stable isotope discrimination factor of wild organisms: a case study of the red swamp crayfish in integrated rice–crayfish (Procambarus clarkii) culture without artificial diets

Abstract

ABSTRACT This study collected samples from a 95-day integrated rice–crayfish culture experiment, and determined the stable isotope discrimination factor of the red swamp crayfish (Procambarus clarkii) by using a model method and difference value method. The isotope ratios of P. clarkii and the dietary resources in rice fields and its feeding niche volumes were ‘conservative’ as proposed. This result broadly supported the assumption of the laboratory feeding experiment that animals should be fed a single diet exhibiting a constant isotopic composition. Using standard ellipse areas (SEA) to screen the data, growth- and time-dependent models of carbon and nitrogen isotopes of females and males were obtained. The Δ13C and its half-lives for females and males were 0.67 (21.0 d) and 0.91 (33.0 d), whereas Δ15N and its half-lives for those were 3.45 (17.8 d) and 3.05 (17.3 d), respectively. The results of integrated rice–crayfish culture without artificial diets provides a reference example for future studies on species-specific discrimination factors in specific field habitats.