Due to the importance of diversifying the feed input matrix for aquaculture through low-impact local biomass, the effect of replacing corn flour with Lemnaminor flour in diets for juvenile Piaractus brachypomus was evaluated. Four isoprotein diets were formulated with 0% (T0), 25% (T1), 50% (T2) and 100% (T3) replacement and administered to 240 fish grown at 10 fish m³ for 75 days. Animals were fed 5% of their body weight, twice a day. Weight gain, specific growth rate (SGR), apparent feed conversion (AFC), protein efficiency (PE), hepatosomatic index (HSI) and survival were recorded. The results show that partial replacement (T1–T2) maintained the final biomass (2.45 ± 0.09 kg), TCE (2.60 ± 0.11% d), AAC (1.81 ± 0.06) and EP (2.24 ± 0.05) without differences compared to the control. In contrast, total replacement (T3) reduced biomass by 24%, apparent intake by 20% and increased I...