To determine the factors influencing the productivity of fish in rice paddies (rice-cum-fish) in Laos, this study conducted aquaculture trials using an indigenous fish (Anabas testudineus) in Feuang and Nasaythong Districts, Vientiane Province, Laos. We evaluated stocking densities (StockD), initial body weights of fingerlings (BWi), stocking durations (duration), and feeding conditions ( fed; feeding or non-feeding), which were considered the factors influencing fish productivity. The final model obtained by variable selection in multiple linear regression included stockD and duration with fed as a fixed effect. Based on a Bayesian framework, the 95% posterior probability intervals (PPIs) showed negative values for stockD (–32.75 to –23.36) and duration (–0.70 to –0.36), and positive values for fed (3.49 to 8.54). These results indicated that (1) stocking density was a primary factor, and higher stocking density reduced fish productivity, (2) longer stocking duration was less contributory to improving fish productivity compared with stocking density, and (3) feeding conditions improved fish productivity, which was suspected to support nutritional deficiency in the natural food items (e.g., aquatic insects, crustaceans) in paddies. Our findings suggested that fish productivity could be improved by lower stocking density, and that feeding had the potential to maintain high productivity with low stocking density and longer stocking duration.