Design and Performance of an Indigenous Water Recirculating Aquaculture System for Intensive Production of Nile Tilapia, Oreochromis niloticus (L.), in Saudi Arabia
Al-Hafedh, Y. S.
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The increasing demand for fish, and the scarcity of fresh water in Saudi Arabia both press the need to adapt new technologies for intensive water recirculating aquaculture to maximize water recycling and increase fish production. Using locally available materials, a commercial-scale recirculating aquaculture system was developed in triplicate to produce Nile tilapia. The system was operated to produce more than 50 kg fish/m3/cycle, and the filters were evaluated for their efficiency in removing organic wastes from the effluent. Each replicate consisted of a culture tank, two mechanical filters with sand/gravel medium, two submerged biofilters with plastic media, a sump and two pumps. Mixed sex tilapia with an average size of 76.4 g were stocked at a density of 188 fish/m3 and fed a 34% protein diet at 3% body weight per day (initially). Water temperature was maintained at 28 ± 1°C, water flow rate was adjusted to 300 liters/min and the culture tank and biofilter were aerated. Water samples were collected from the inlet and outlet of each component and were analyzed for important parameters. Values (± SE) of total ammonia nitrogen (TAN) (0.98 ± 0.1 ppm) and nitrite-nitrogen (NO2-N) (0.48 ± 0.02 ppm) in the fish culture tanks were within the acceptable limits, while the other water quality parameters were also maintained under normal range by the filtration system. Removal rates (± SE) of 186.7 ± 31.59 g TAN/m3/day and 66.53 ± 16.9 g NO2-N/m3/day, respectively, as well as TAN and NO2-N removal efficiencies (31.45 ± 2.32% and 21.05 ± 3.8%, respectively) were measured across the PVC biofilter medium. The area specific TAN and NO2-N removal rates (± SE) or nitrification rates (0.34 ± 0.06 g/m2/day and 0.15 ± 0.05 g/m2/day) for the biofilter were comparable with the performance of other commercial intensive recirculation systems. Mean final weight (±SE), final biomass, growth rate, SGR, FCR, and percent survival for the mixed-sex tilapia were 277.21 (1.76) g/fish, 50.21 kg/m3, 1.34 g/fish/day, 0.86%, 1.89, and 96.53%, respectively, whereas the average water use was 0.4 m3/kg of fish production. Locally available materials were found to be appropriate for solid and organic waste removal. More than 85% of the system water volume could be recycled daily, while fish production per unit space was also multiplied 3-6 fold compared to the traditional culture practice.