Aquatic plants for bioremediation in red hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus) recirculating aquaculture

This study investigated using aquatic flowering plants (Canna generalis L., Typha angustifolia L., Echinodorus cordifolius L. and Cyperus involucratus [Rottb].) for nitrogenous waste removal from tropical aquaculture fishponds. Two plants which had higher removal efficiency (Canna generalis L. and Echinodorus cordifolius L.) were selected for further study in different light intensities and substrates. The effects of different light intensities were significantly different (P < 0.05), and Canna generalis L. and Echinodorus cordifolius L. had efficiencies of removal of ammonia, nitrite and nitrate of 44.9–91.2, 90.8–99.3 and 55.7–98.5 %, respectively. In experiments using different densities of plants, Echinodorus cordifolius L. had a higher efficiency of removal of nitrogenous waste than Canna generalis L. for a given biomass under shaded conditions (92.5–185 µmol photon m−2 s−1 PAR) compared with high light conditions (185–740 µmol photon m−2 s−1 PAR). A red hybrid tilapia fish pond-planted pond dual-tank experimental setup modeled an aquacultural recirculating system. Planting densities of 3–12 plants m−2 all improved water quality (P > 0.05), but higher planting densities were counterproductive in terms of both water quality and fish survival. Flow rates of >100 % day−1 were needed for efficient nitrogenous waste removal. Red hybrid tilapia in the optimal setup (50 fish m−2, 12 plants m−2, 100 % water turnover per day) had weight gains of 629 %, a survival rate of 82.7 %, a feed conversion ratio of 0.72, and a specific growth rate of 4.7 % day−1 over a 6-week experimental period.