Effect of water flow rate on polyculture of koi carp (Cyprinus carpio var. koi) and goldfish (Carassius auratus) with water spinach (Ipomoea aquatica) in recirculating aquaponic system

A 45-day experiment was conducted for standardization of water flow rate for koi carp (Cyprinus carpio var. koi) and gold fish (Carassius auratus) along with water spinach (Ipomoea aquatica) in water recirculating aquaponic system. Different flow rates, viz., 0.8, 2.4, and 4 l min−1, were assigned as T1, T2, and T3, respectively, with stocking density ratio of 1:2 for koi carp and goldfish. Treatment T1 showed maximum fish growth in terms of percentage weight gain and specific growth rate. Plant height, percentage height gain, and yield of water spinach plants were observed highest in treatment T1 as compared to T2 and T3. All the treatments effectively removed nutrients, but treatment T1 showed maximum percentage of nutrient removal (NO3-N, PO4-P, and K). The plant growth and nutrient removal were increased with decrease in flow rate. Flow rate in T1 (0.8 l min−1) showed the highest growth in both fish species. Thus, 0.8 l min−1 can be suggested as optimum water flow rate for the polyculture of koi carp and goldfish with water spinach in an aquaponic system.