Distributing locally grown food fish live may provide aquaculture producers in Kentucky a more profitable market opportunity than selling fish as a commodity. Holding fish live in recirculating systems will be required for this approach. Fluidized bed filters are expected to be a useful tool with regard to shock loading of these systems. In this study, investigators conducted experiments with hybrid catfish (channel x blue) held at 15 and 20°C with and without a small fluidized sand filter.
After simulated hauling for 3 hours, food size hybrid catfish were stocked at 40 kg/m3 in recirculating aquaculture systems with an Aquadyne 17 L bead filter. An RK10 fluidized sand filter (15 cm x 180 cm) with 14 kg sand was installed inline in half of the tanks. Holding tank water was oxygenated, supplemented with salt at 4 ppt, and maintained at a temperature of 15 or 20°C in separate experiments for a period of 8 days each. Water quality for each holding tank was measured at stocking and daily thereafter (24, 48, 72, 96, 120, 144, 168, and 192 hours). Total ammonia nitrogen (TAN), unionized ammonia (UIA), nitrite, nitrate, temperature, dissolved oxygen, pH and conductivity was measured daily. Alkalinity, hardness, CO2 and turbidity was measured every other day. Fish were not fed during the experiments.
At 15°C, TAN rose steadily to 10 mg/L in the control treatment and about 6 mg/l in the fluidized bed treatment. In the fluidized bed treatment, UIA stabilized at hour 120 at about 0.07 mg/L and slowly declined thereafter. Nitrite and Nitrate increased and pH decreased throughout the experiment. Mean weight loss was 1.78%.
At 20°C, TAN rose steadily to 5 mg/L in the control treatment and about 6.5 mg/L in the fluidized bed treatment. In the fluidized bed treatment, UIA stabilized at hour 72 and decreased rapidly after hour 96. Nitrite stabilized at hour 168 and began to decrease in both treatments. pH decreased throughout the experiment. Mean weight loss was 3.64%.
Addition of the fluidized bed filter did not significantly decrease TAN or UIA during the eight day holding period. Water temperature influenced the rate of nitrification more than installation of the small fluidized bed filter.