Abstract
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.
Highlights
The aquaculture industry is one of the fastest growing agriculture sector globally
Two litres of aquaculture wastewater were collected in sampling bottles at the point of discharge and were analyzed for the following physicochemical parameters: Dissolved Oxygen (DO), Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), phosphate, sulphate, Total Ammonia Nitrogen (TAN), nitrate, Total Suspended Solid (TSS), pH and temperature were monitored weekly before the commencement and after the bioremediation process according to APHA [35] standard procedure
The mean values of phosphate, nitrate, sulphate, TAN, biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total suspended solids (TSS) measured in the raw aquaculture wastewater (RAW) were significantly higher than the values observed in the treatment
Summary
The aquaculture industry is one of the fastest growing agriculture sector globally. With a total production of 66.6 million metric tonnes in 2012, it provides almost half of all fish production for human consumption [1]. The long-term sustainability of aquatic environment has raised concerns over the environmental impact of this vital sector, due to its negative impact on aquatic ecology and systems [2,3]. This is because intensification of aquaculture involves the use of highly nutritious feeds and other chemical products, which generate wastes that, in most cases, are difficult to curtail and toxic to aquatic lives [4,5,6]. The amount of wastes generated from aquaculture practices depends on the culture system characteristics, choice of species, feed quality and management practices [8]
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