Résumé
Determining the optimal combination and proportion of species remains a key challenge for balancing and optimizing nutrient recycling in polyculture systems. The aim of this study was to evaluate diet, food-source utilization, and trophic interactions of tambaqui (Colossoma macropomum) reared in monoculture or in polyculture with curimba (Prochilodus lineatus), using carbon and nitrogen stable isotopes and Ecopath modeling. Three production systems were compared: tambaqui monoculture (0.25 fish m -2 ) (T), and tambaqui-curimba polycultures with high (0.25 fish m -2 ) (TC) and low (0.08 fish m -2 ) tambaqui final densities (TLC). Across all treatments, tambaqui production was primarily supported by feed (<85%), while curimba growth relied on live or dead zooplankton. However, in TLC, the contribution of zooplankton to the curimba diet significantly decreased (from 68% in TC to 44% in TLC), while formulated feed increased (from 5% in TC to 24% in TLC), resulting in an overlap of isotopic niches between both fish species. Polyculture promoted higher ecotrophic efficiency of both feed and zooplankton, as well as higher system omnivory and Finn's cycling index. Polyculture may promote more efficient utilization of natural food resources in the ponds and lead to higher yields compared to monoculture. A high tambaqui density in polyculture (0.25 tambaqui m -2 with 0.30 curimba m -2 ) minimizes competition with curimba for formulated feed, while enhancing nutrient recovery and overall system efficiency.