Objective To explore the rice field adaptive characteristics of Cyprinus carpio var. Jinbei (goldenback carp), as well as the relationship between their gut and different rice field environments.

Method The study focused on the growth of goldenback carp in flat plate, “single line” ditch, and “cross-shaped” ditch rice fields, using morphological, enzymatic and bioinformatics methods to investigate the effects of adding ditches and pits in rice fields on the intestinal structure, digestive enzyme activities and microbial communities of the goldenback carp.

Result The villus width of goldenback carp intestine in “cross-shaped” ditch group was the widest (173.59 μm), followed by the “single line” ditch group (157.72 μm), and the flat plate group was the narrowest (139.69 μm). The trypsin activities of the “cross-shaped” ditch group and the “single line” ditch group were 4 662.65 and 4 676.12 U·mg⁻¹ respectively, significantly higher than that of the flat plate group (3 752.34 U·mg⁻¹) (P<0.05). At the phylum level, after adding ditches and pits in rice fields, Proteobacteria and Firmicutes remained dominant, but Actinobacteria replaced the Bacteroidetes as the dominant phylum. At the genus level, the dominant genera in the flat plate group were Streptococcus, Cetobacterium and Rhodobacter. There were obvious changes in the dominant genera of the “single line” ditch and “cross-shaped” ditch groups, among the top three dominant bacterial genera in each group, one changed in the “single line” ditch, and two changed in the “cross-shaped” ditch.

Conclusion The intestinal structure, digestive enzyme activity, microbial community and dominant bacterial groups of the goldenback carp change with the addition of ditches and pits in rice fields, regulating metabolism to adapt to the new rice field water environments. Despite the changes, the composition of the core intestinal flora of the goldenback carp remains relatively stable.