An integrated recirculating aquaculture system (IRAS) is considered as an alternative solution for efficient utilization of available resources, nutrient recycling and maintaining ecological balance. The effects of using magnetized water on the growth performance of common carp (Cyprinus carpio L.) and water quality parameters were investigated in an IRAS.Six independent IRASs were designed; each system consisted of three tanks: a fish rearing tank, a waste-collection tank and a biological filter tank. An additional crop of macrophyte (Lemna minor) was used as a medium in the biological filter tanks in order to qualify as an IRAS. Two treatments with three replicates were set up in a randomized design. The experimental treatment was supplied with the magnetic field device, while there was no device in the control treatment.The fish growth, feeding efficiency and water quality parameters were measured in all systems. The results revealed that the use of magnetized water in the IRASs increased the specific growth rate of common carp and the growth rate of plants; while, decreased the feed conversion ratio. However, the magnetized water had no effects on the concentrations of ammonium nitrogen, nitrite nitrogen and nitrate nitrogen. The study suggested that the use of magnetized water in the IRASs could be beneficial as a cost-effective technique to increase the profitability of the system.
The harvesting of plant biomass is usually implemented as an effective tool for plant management and removing the nutrients absorbed in plant tissues. Here, the influence of harvesting different biomasses (50%, 33%, 25%, and 0% (no harvest)) of watercress (Nasturtium officinale) was investigated in integrated recirculating aquaponic systems (IRASs) for rearing common carp (Cyprinus carpio). Twelve independent IRASs were designed (4 × 3); each system consisted of a fish rearing tank, a waste collection tank, and a hydroponic bed. Water quality parameters and the growth of both fish and plants were measured in all the systems, and then the nutrient removal capacities of the hydroponic beds were calculated. The results revealed that increasing the biweekly harvested biomass of the plants decreased the growth of the watercress, while it did not affect the growth of the common carp. Increasing the harvested biomass of the plants also decreased the nitrate nitrogen and orthophosphate removal efficiencies of the aquaponic systems, while it did not affect the ammonia and nitrite nitrogen removal efficiencies. Therefore, a biweekly harvesting of less than 25% of the biomass of the growing watercress is recommended for efficient nutrient removal and the sustainable growth of both watercress and the common carp in aquaponic systems.
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