Food sources of common carp in a Hani Terrace integrated rice-fish system (Yunnan Province, China)

Integrated rice-carp farming is commonly employed on Hani terraces in China. However, the altitude within a Hani terrace can vary greatly, and thus the solutions for such a farming approach must vary with altitude. Research on common carp food sources in an integrated rice-carp farm at different altitudes helps to understand the food requirements of carp across periods and provides guidance for production. In this study, the composition of eukaryotic food sources of common carp (Cyprinus carpio) growing on Hani rice terraces at low and high altitudes (570 m and 1840 m) from May to August 2019 was surveyed by high-throughput DNA sequencing. The 18 s v4 gene sequences were amplified to provide 2243,095 valid reads and 2485 operational taxonomic units. In addition, the relative abundance of the gut contents of each food source varied by month and altitude. Chlorella, Necator, Oedogonium, Oryza and Scenedesmus were the dominant C. carpio food sources at the high altitude, while Chironomus, Gieysztoria, Scenedesmus, Oryza, and Lemna were the dominant species at the low altitude. The Lemna biomass identified in the C. carpio gut contents in the low altitude terrace decreased from 39.75% in June to 0.05% in August, while the Oryza biomass increased with time. The Oryza biomass observed in the gut contents of C. carpio growing in high and low altitude terraced fields increased with time. Rice pests, including the rice gall midge, rice bugs, nematodes, and chironomid larvae were found in the stomachs of C. carpio in the high and low altitude terraced fields. The maximum proportion of chironomid larvae in the gut contents of C. carpio in the low altitude terraces reached 39.29%, while the maximum proportion of nematodes was 5.38%. However, only chironomid larvae and nematodes were found in the gut contents of C. carpio growing in the high altitude terrace, reaching maximum proportions of 0.17% and 3.63%, respectively. Furthermore, a variety of rice pests were detected in the gut contents of C. carpio, indicating that C. carpio effectively preyed on rice pests and reduced rice diseased in the integrated rice-carp farming terraces. •The eukaryotic composition in the gut content of C. carpio differed among months, and also between altitudes.•Chlorella, Necator, Oedogonium, Oryza and Scenedesmus were dominant food resources of C. carpio at high altitudes.•Chironomus, Gieysztoria, Scenedesmus, Oryza and Lemna were dominant food resources of C. carpio at low altitudes.•Ri