Iron and potassium doses optimization and its effect on growth and production of pangasius (Pangasianodon hypophthalmus) and basil (Ocimum basilicum L) in a nutrient film technique based aquaponics

A 120-day experiment evaluated the effects of varying iron dosages with constant potassium fertigation on pangasius (Pangasianodon hypophthalmus) and basil (Ocimum basilicum L) in a nutrient film technique based aquaponic system. Four iron dosages, i.e. 1.0, 1.5, 2.0, and 2.5 mg/L, were assigned as T1, T2, T3, and T4, respectively, with a constant potassium dose of 150 mg/L and compared to control (without supplementation). The pangasius and basil were stocked at densities of 3.00 kg/m³ and 24 plants/m², respectively, in each treatment group. Results showed the highest mean body weight of fish was recorded in T2 (28.79 ± 0.34 g), which was similar to T3 (28.34 ± 0.31 g), while the control group had the lowest mean body weight (25.23 ± 0.38 g). Basil yield was highest in T3 (583.76 ± 6.96 g) during the third harvest, followed by T2 (566.41 ± 8.45 g), with the control yielding the least (250.55 ± 4.64 g). Water quality parameters (e.g., pH, dissolved oxygen, temperature) remained within acceptable ranges for aquaponic system throughout the study. Iron-potassium supplementation improved the uptake of basil nutrients like phosphorus, nitrogen, potassium, iron, copper, zinc, manganese, sulfur, and boron. Significantly higher carotenoid, chlorophyll a, and b content of basil leaves were recorded in T3 compared to the control. Fish stress markers were highest in T4. Considering the fish body weight, basil yield, water quality, nutrient uptake, chlorophyll content, and fish stress parameters, the optimal iron concentration for basil and pangasius in this system was found to be 1.5–2 mg/L (T2 and T3) with 150 mg/L potassium.