Resource utilization, competition and cannibalism of the red swamp crayfish Procambarus clarkii in integrated rice-crayfish culture without artificial diets

In a 95-day, integrated rice-crayfish (Procambarus clarkii) culture experiment, the changes in the contribution of feed sources, intra-sexual isotopic niche width, inter-sexual isotopic niche overlap, and potential competition were analyzed. The contribution of plants available for crayfish decreased over the culturing time, whereas the contribution of animal feed sources increased accordingly, and that of the cannibalized feed sources increased initially and then decreased. In contrast, the contribution of detritus as a feed source decreased initially and then increased. Female crayfish made higher contributions to inter-sexual cannibalism than intra-sexual cannibalism on August 28 and September 24, whereas these contributions were higher for male crayfish on September 24 and October 20. Double inter-sexual cannibalism occurred in the middle and later periods of the trial. The isotopic niche of crayfish ascend in the direction of the δ15N axis on September 24 and then decreased and contracted by October 20. The isotopic niche of males and the total population decreased over culturing time, occupying a larger isotopic niche than females at the same time point, and the isotopic niche of males decreased more slowly than that of females. The inter-sexual overlap of the isotopic niches decreased initially and then increased. The contribution of inter-sexual cannibalism was the highest, and the inter-sexual overlap of the isotopic niches was lowest on September 24. Moderate inter-sexual cannibalism could reduce inter-sexual overlap of the isotopic niche and potential competition for resources. This study is the first to investigate the feed sources and intra- and inter-sexual isotopic niches of P. clarkii in rice fields without artificial diets for crayfish, with a view to providing insights for further research on the interplay between cannibalism and competition between male and female crayfish.