Includes bibliographical references.

In Arunachal Pradesh, the Apatani tribe, has been practicing "Paddy-cum-Fish Farming" for centuries in the Ziro Valley of Lower Subansiri District. In this innovative system, two popular varieties of rice i.e., Mipya & Emoh and fish variety i.e., Ngihi, were utilized for farming in same plot of land (GoI., 2019). Out of 715.7 ha of wet area, around 592 ha (48.38%) has utilized this farming system in the Ziro Valley. UNESCO has tentatively listed that Ziro Valley is a “World Heritage Site” based on its picturesque landscape, unique water management, and sustainable agricultural practices (UNESCO., 2022). This system of farming is totally organic and free from application of synthetic chemical inputs (Saikia and Das, 2004). With this background, the following research objectives were formulated: (1) To study the cost and returns of paddy-cum-fish farming; (2) To analyse the resource use efficiency of paddy-cum-fish farming and (3) To identify the constraints faced by the farmers in paddy-cum-fish production. The present research was carried out in eight villages of Ziro-I and Ziro-II blocks in Lower Subansiri District. A sample of 100 respondents was chosen using a random sampling technique. Primary data was gathered through pre-structured standardized interview schedule. To achieve the above-mentioned objectives, analytical tools like Cost Concepts, Cobb-Douglas production function and Garett ranking were applied. The study found that, per hectare gross returns for paddycum- fish farming were ₹287,848.69 for small farms, ₹277,588.92 for medium farms, ₹273,756.96 for large farms, and ₹280,272.53 overall. The benefit-cost ratios were found to be 2.34 for small farms, 2.18 for medium and large farms, and 2.17 for overall. In all farm size, certain inputs were underutilized while others were overutilized. Farmers faced major constraints like high labour cost, flooding and breakage of bunds, shortage of labour, and poor contact with extension workers. Therefore, there is potential to boost the productivity of paddy and fish in the region by increasing the usage of underutilized inputs and decreasing the over-utilized inputs. The study recommended enhancing farmers' engagement with extension agents and to provide practical training.