Biological Treatments of Fish Farm Effluent and its Reuse in the Culture of NileTilapia (Oreochromis niloticus)

Aquaculture wastewater collected from a catfish farm in Ibadan metropolis was treated with duckweed, Lemna minor (Td) for two weeks and thereafter used in the culture of Nile tilapia (O niloticus). The performance of O niloticus raised in Lemna minor treated waste water was compared with bacteria-treated waste water, Bacillus sp. (Tb) and well water (Tc) as control (untreated). The Bacillus sp. was isolated from the catfish wastewater, and was positive to Gram’s staining, catalase and glucose fermentation test. Nile tilapia juveniles (n=54) of an average initial weight of 10.43 ± 0.04 g were stocked in triplicates per treatment and fed to satiation twice daily for 8 weeks. There was significant difference (P<0.05) in the quality of waste water in all the treatments. Compared to initial waste water, Td showed a significant reduction in biological oxygen demand, BOD (1.23 ± 0.03 mg/L vs. 36.80 ± 1.89 mg/L), chemical oxygen demand, COD (2.20 ± 0.06 mg/L vs. 58.81 ± 1.89 mg/L), sulphate (0.50 ± 0.06 mg/L vs. 5.53 ± 0.33 mg/L) and phosphate (5.40 ± 0.31 mg/L vs. 18.43 ± 0.78 mg/L) after 2 weeks of treatment. The level of phosphate, BOD, COD, nitrate, and TSS were lowest in Td compared to Tb and Tc (P<0.05). The lowest level of ammonia was obtained in Tc (0.15 ± 0.10 mg/L), compared to Td (0.15 ± 0.10 mg/L) and Tb (0.66 ± 0.28 mg/L). The highest percentage weight gain (WG) of 34.37 ± 0.60% and the lowest feed conversion ratio (FCR) of 1.59 ± 0.03were recorded in fish raised in Td (P<0.05). Oreochromis niloticus juveniles raised in Td also had the highest specific growth rate (SGR) of 0.23 ± 0.01% compared to 0.19 ± 0.00% recorded in fish raised in both Tb and Tc. Fish raised in Tc had the highest survival rate (100 ± 0.00%) compared to the fish cultured with Tb (77.80 ± 2.30%) and Td (72.20 ± 1.95%). The research findings suggest that Lemna minor could be used in fish culture with positive effect on water quality and growth performance.