Field distribution characteristics and influencing factors of crayfish in rice-crayfish integrative system

Transformation of food systems will be required to feed the burgeoning global population in the coming decades. Co-culture systems enable production of multiple types of food within the same land area. One such co-culture production system -rice-crayfish integrative system (RCIS) -has seen recent emergence and rapid growth in Asian countries. As yet, however, there remains a paucity of information on how crayfish distribute across paddy fields, even though such information is key in management of crayfish feeding, rice planting and environmental protection. Here, we conducted a 2-year field experiment to gain insight into the spatial distribution of crayfish using cage trapping and LED tracking. We had four key observations: (1) spatial distributions of crayfish across fields were heterogenous, (2) the individual weight of crayfish per ground cage was normally distributed and there was a linear relationship between the number and weight of crayfish captured in different ground cages, (3) distribution characteristics of crayfish altered diurnally, with night capture of the mid columns being higher than that of the side columns, and with day capture being less than that measured at night (rows 1, 2, 14 and 15 near the short inner ridge was always higher than that of other rows) and (4) cumulative capture in each ground cage was linear with water depth (P<0.001) but there was no significant correlation with other environmental in-dicators, including temperature, pH, dissolved oxygen (DO), salt, total dissolved solids (TDS), conductivity (CON), turbidity and fresh weight of aquatic plants. We conclude that spatial distributions of crayfish in RCIS were closely related to water depth and field topography, with the highest densities realized in gullies within 6-7 m of the short ridge of rectangular farmland. Co-culture farmers can adjust their feeding and capturing strategies based on the distribution characteristics reported here, thereby reducing feeding costs, improving labor effi-ciency and mitigating detrimental environmental impacts.