Abstract
In aquaponic systems, plants absorb dissolved nutrients from aquaculture wastewater for their growth. The removal of nutrients allows reuse of water and minimises wastewater discharge to the surrounding environment. This study evaluated the relative nutrient removal efficiencies of three plant species and the performance of Nile tilapia (Oreochromis niloticus) in a small-scale aquaponic system. Three aquaponic systems were assigned as treatments PU (pumpkin), SW (sweet wormwood) and AM (amaranth). Physical-chemical water quality parameters were measured in the fish tanks as well as hydroponic inlets and outlets. Fish sampling was done every 2 weeks for 60 days. Results showed significantly (p < 0.05) lower nutrient concentrations in the hydroponic outlets than the inlets. There was no significant difference in nutrient removal efficiency of the plants (p > 0.05) for all the tested nutrients except for phosphorus. Phosphorus removal was substantially high in PU (75.5 ± 16.8%) than SW (47.36 ± 14.5%) and AM (40.72 ± 13.2%). In addition, the SW system had better (p < 0.05) relative growth rate (0.06 ± 0.00) than that of PU (0.05 ± 0.00) and AM (0.05 ± 0.00). Nitrogen and phosphorus content in plant tissues was significantly high (p < 0.05) in SW and PU plants respectively. Water quality parameters had a significant influence on the growth of fish (p < 0.05). The growth of fish was not different (p > 0.05) in the three treatments. The findings indicate that the tested plants can reduce nutrients in aquaculture discharge water.
Highlights
Aquaculture has been proposed as the only way of ensuring that the increasing global demand for fish is met (FAO 2016)
Our findings indicate that sweet wormwood had high nitrogen utilization efficiency (NUE) due to the significantly high nitrogen content which translated to high growth rates than amaranth and pumpkin
The findings of this study show that pumpkin, sweet wormwood and amaranth were able to absorb nutrients from aquaculture wastes
Summary
Aquaculture has been proposed as the only way of ensuring that the increasing global demand for fish is met (FAO 2016). There are many environmental concerns with conventional aquaculture including the frequent exchange of nutrient-rich water with freshwater from adjacent water bodies to provide optimum conditions for fish production (Konnerup et al 2011). The expansion of conventional aquaculture systems depends on freshwater and land resources. Aquaculture development may be constrained by land and freshwater availability (Troell et al 2014; Waite et al 2014). Further development in aquaculture will require the application of improved technologies that can increase fish production, conserve water and reduce environmental impact (Konnerup et al 2011; Trang and Brix 2014; Zou et al 2016)
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