Effects of recirculation rates on water quality and Oreochromis niloticus growth in aquaponic systems

The present study examined the effects of three recirculation rates (50%, 200% and 400%) on water quality and biomass growth at low and high fish stocking densities (122 and 220 fish/m 3 ) in aquaponic systems. The system consisted of a Tilapia tank connected to a gravel filter and three hydroponic trenches in series with Ipomoea aquatica , Lactuca sativa and Canna glauca . The RRs influenced most water quality parameters with best water quality at the high RR. At the low RR of 50% mass mortality of fish occurred due to lack of oxygen. The fish growth and survival was excellent in the high RR of 400% at the low fish density of 122 fish/m 3 . The plant trenches were found to be effective in removing potential harmful concentrations of NH 4 -N and NO 2 -N from the recirculating water. For each kg of fish produced in this system approximately 1.0 m 3 water was needed. During a 25-day period about 1 kg of marketable fresh biomass of I. aquatica and 270 g dry weight aboveground biomass of C. glauca was produced. It is concluded that high recirculation rate of the water of 200–400% per day is needed to secure a good growth and a low FCR of Tilapia in aquaponic systems. High recirculation rates also secure a good water quality. The aquaponic system has a very low effluent discharge compared to traditional aquaculture techniques, and it recycles nutrients for plant growth. Hence, aquaponic system is a promising sustainable solution that can be applied on commercial fish pond scale.