Optimization of stocking density of koi carp (Cyprinus carpio var. koi) with gotukola (Centella asiatica) in an aquaponic system using phytoremediated aquaculture wastewater

The stocking density of koi carp (Cyprinus carpio var. koi) was optimized with gotukola (Centella asiatica) in an aquaponic system using phytoremediated aquaculture wastewater. Fingerlings of koi carp were stocked in different stocking densities as 1.4 (T1), 2.1 (T2), 2.8 kg m−3 (T3), and the control (1) 1.4 kg m−3(C1) without hydroponic component. The control 2 (C2); plant grown in field condition was assigned to compare the efficiency with aquaponics. The highest length (10.79 ± 0.24 cm) and weight gain (12.53 ± 0.19 g) in fish were observed in T1 and the highest nitroblue tetrazolium (NBT) activity of the fish was found in T1. However, the highest catalase activity, glucose, and cortisol level were obtained in (T3), which concluded that the fish growth was significantly affected by the highest stocking density. However; the medium stocking density (T2) didn't show a significant difference with the lowest stocking density (T1). In contrast to the biomass of koi carp, the yield of C. asiatica increased significantly with fish stocking density. The highest yield (203.76 ± 11.03 g) was obtained by the maximum stocking density (T3) but it was not significantly different from T2. Considering the water quality parameters, nutrient dynamics, plant growth as well as fish health monitoring parameters, the stocking density of 2.1 kg m−3 (T2) could be suggested as the optimum stocking density for this system. •The stocking density is a key factor for providing an adequate amount of nutrients to the fish and plants in aquaponics.•The stocking density of 2.1 kg m − 3 could be taken as the optimum stocking density for gotukola and koi carp in aquaponics.•Phytoremediated aquaculture wastewater with freshwater enhances the productivity of fish and plants in aquaponics.