Influence of aeration flow rates on Oreochromis niloticus growth in indoor recirculating aquaculture system

Aeration flow rate is the crucial controlling factor for aerated push-flow recirculating aquaculture system. In order to explore the effects of aeration flow rates on fish growth and flesh quality, a 56-days experiment was conducted with self-designed indoor recirculating aquaculture system model at 3 aeration flow rates (0, 30 and 50 L/min, respectively), where the growth performance and flesh quality of tilapia (Oreochromis niloticus) were monitored. The results showed: ① the final body weight and specific growth rate of tilapia in the 30 L/min condition were (79.56±3.82) g and (2.81±0.54)%/d, while the specific growth rate was 11.07% and 8.49% higher than those in the 0 and the 50 L/min conditions. At the same time, the total protein and triglyceride concentrations in the 30 L/min condition were higher but the urea nitrogen concentration was lower, e.g., on the 56^th day, the TP concentrations were 57.43% and 10.43% higher than those in the 0 and 50 L/min conditions, as for TCHO concentration, the increments were 22.19% and 12.32%, respectively. However, the BUN concentration decreased by 39.02% and 37.50%. Furthermore, the glucose concentration was not significantly affected by the aeration flow rates, but the alanine aminotransferase and aspartate aminotransferase concentrations in the 50 L/min condition were higher than those in the other conditions; ② the hardness, springiness and chewiness of the fish in the 30 L/min condition were significantly higher than those in the 0 L/min condition on the 56^th day, e.g., the hardness was 27.10% and 15.85% higher than that in the 0 and 50 L/min conditions, as for the springiness and the chewiness, the increments were 9.10% and 3.54%, 42.25% and 24.06% respectively, but the resilience was slightly higher in the 50 L/min condition than that in the other groups. Through analysis of test results, the growth rate of O. niloticus was slow due to lack of water stimulation and dissolved oxygen concentration at the low aeration flow rate (0 L/min), while the consumption of nutrients of tilapia was accelerated at the high aeration flow rate (50 L/min), only at the moderate aeration rate flow (30 L/min), the tilapia attained better growth performance and flesh quality.