In this study, we aimed to develop a novel modified flow-through aquaculture system to reduce excessive water exchange rates and address uncontrollable water quality issues associated with traditional flow-through aquaculture systems. The new system was designed to reduce the water exchange rate from 24 to 9 cycles per day by equipping it with CO2 degassing towers containing biological media. Additionally, this system was designed to reuse approximately 70% of the wastewater, discharging the remaining 30% into the sea. By discharging wastewater, the system can recover heat, thereby increasing the water temperature in the aquaculture tanks. The system consists of water treatment devices, CO2 degassing towers, filters containing silver nanoparticle, heat exchange devices, cooling and heating units, and medium-pressure UV lamps.
To verify the performance of the low-water flow-through aquaculture system based on feed supply amounts for olive flounder, various preliminary experiments were performed over 43 days, from June 2 to July 13, 2024, with a total of 3,180 flounder (body weight: 75.1 ± 5.7 g) placed in four tanks. The stocking density was 50 fish/m3, and the water exchange rate in the tank was 3.1 m3/h (6.7 cycles/day). Water temperature and salinity were 21.53 ± 0.38℃ and 31.37 ± 0.43 psu, respectively. The feed supply amounts were set at 1.33% (800 g), 1.67% (1,000 g), and 2% (1,200 g) of the flounder’s body weight. Changes in the dissolved oxygen (DO), pH, turbidity, and total ammonia nitrogen (TAN) in breeding water were measured every 4 days according to the feed supply amount. DO, pH, and turbidity were measured using the YSI-ProDSS sensor, and TAN was analyzed using Nessler’s reagent with the DR3900 spectrophotometer (HACHⓇ). As a result, when the feed supply was 1.33% of body weight, DO and pH decreased from 7.05 to 6.80 mg/L and from 7.63 to 7.60, respectively, while turbidity increased from 0.57 to 0.83 NTU. When the feed supply was 1.67% of body weight, DO and pH decreased from 6.56 to 6.20 mg/L and from 7.62 to 7.59, respectively, with turbidity increasing from 0.81 to 1.07 NTU. Additionally, when 2% of body weight feed was supplied, DO and pH decreased from 6.7 to 5.98 mg/L and from 7.69 to 7.53, respectively, while turbidity more than doubled, increasing from 0.90 to 1.84 NTU. Meanwhile, TAN remained between 0.03 and 0.3 mg/L, well below the design threshold of 2 mg/L in all experiments. Further studies will be conducted to investigate the water quality characteristics of low-water flow-through aquaculture systems.