Effects of stocking density on growth performance of hybrid catfish (Clarias macrocephalus x C. gariepinus) in a smart recirculating aquaculture system using black soldier fly larvae as fishmeal replacement

Abstract

This study investigated the effects of different stocking densities on the growth performance of hybrid catfish (Clarias macrocephalus × C. gariepinus) in a smart recirculating aquaculture system (Smart RAS), using black soldier fly larvae (Hermetia illucens) as a 75% replacement for fishmeal. The experiment was conducted with three stocking densities of 50, 100, and 150 fish/m² in a 5 m³ culture tank equipped with physical filtration (Drum filter), biological filtration (MBBR), and UV sterilization, controlled by a PLC integrated with IoT technology. Results indicated that final average weights (325.56±9.75 and 322.98±12.63 g/fish) and specific growth rates (4.78±0.03%/day) of catfish stocked at 50 and 100 fish/m² were not significantly different (P>0.05), but were significantly higher than those stocked at 150 fish/m² (282.49±4.29 g/fish and 4.66±0.01%/day, respectively; P<0.05). Survival rates at densities of 50 and 100 fish/m² (91.56±3.36% and 88.33±3.93%, respectively) were significantly higher (P<0.05) compared to the 150 fish/m² group (75.26±6.80%). Throughout the study period, the automated control system effectively maintained water quality parameters, with dissolved oxygen (DO) between 3.72–4.27 mg/L, pH between 7.11–7.56, and total ammonia nitrogen (TAN) between 0.36–0.45 mg/L. Economic analysis revealed that the stocking density of 100 fish/m² provided the highest return on investment (ROI) at 53.55%. Thus, stocking hybrid catfish at 100 fish/m² in a smart RAS using black soldier fly larvae to replace 75% of fishmeal is recommended, as it maximizes production, maintains optimal water quality, achieves the best feed utilization efficiency, and offers the highest economic returns.