Evaluating and modeling pacu (Piaractus mesopotamicus) growth in intensive floating cage culture: A nonlinear approach for lotic freshwater systems

Pacu (Piaractus mesopotamicus) is traditionally farmed in ponds, but floating cages (intensive productive systems) are gaining momentum. This study evaluated the growth performance of P. mesopotamicus reared in floating cages in lotic freshwater system conditions and identified the most suitable nonlinear growth model. Small-scale production systems were monitored over three grow-out cycles (2021-2024), comprising 13 floating cages (14 m³) installed in secondary channels of the Middle Paraná River. Approximately 3,600 juveniles (initial weight: 168.1 ± 89.3 g) were stocked at a density of ~21 fish m-³ and fed commercial diets under a two-phase feeding protocol. Fish were sampled monthly for weight, length and condition. Marketable size (~1 kg) was reached within a production window of 3 to 5 months (129 ± 13 days). The mean specific growth rate was 0.97 ± 0.39% day-1 and the feed conversion ratio was low (1.78 ± 0.73 kg kg-1). Final biomass density reached 20.2 kg m-³. Growth was best described by a Gompertz model, with an asymptotic weight near 1.2 kg. Significant improvements in condition indices were recorded. These findings support the feasibility of expanding pacu aquaculture in cage freshwater systems as a sustainable protein source and development opportunity for local economies.