Treatment of Aquaculture effluent using an integrated system: fish-phytoplankton-zooplankton

Aquaculture development during the last decades has led to an increase in aquaculture effluents into water bodies. Treatment of these effluents and reusing them in culture systems can decrease the level of destructive impacts on aquatic ecosystems. The present study was conducted to investigate the possibility of using phyto- and zooplankton microorganisms to treat and reuse fish culture wastewater in an integrated culture system. The Nile tilapia (Oreochromis niloticus) and Chlorella vulgaris were used as fish and microalgae species. The main zooplankton classes were composed of artemia (Artemia franciscana) and rotifer (Brachionus sp.). Measured and calculated parameters were: nitrate (NO3), nitrite (NO2), ammonium (NH4), phosphate (PO4), dissolved oxygen (DO), pH, electrical conductivity (EC), total dissolved solids (TDS), total suspended solids (TSS), number of microalgae cells and zooplankton counts, and fish growth performance parameters include weight gain (WG), specific growth rate (SGR) and condition factor (CF). The results showed that nutrient levels (NO2, NO3, and PO4) were significantly (P < 0.05) lower at the system outlet than control condition during the study period. The DO and pH levels were observed at their optimum ranges (DO > 6 mg.l-1; pH = 7 - 8) during the study period. The levels of EC, TDS and TSS of the integrated system were significantly (P < 0.05) lower than the control condition. The growth performance (i.e. weight gain) of fish was significantly (P < 0.05) better in the integrated system compared to the control condition. It can be said, based on the obtained results, simultaneous use of microalgae, zooplankton, and fish in an integrated tilapia culture system was led to the appropriate treatment of fish culture effluent and significant improvement of water quality to reuse in the system without any undesirable effect on fish growth compared to the control condition.