Effects of flow velocity on growth,metabolism and nitrogen and phosphorus budget of Haliotis discus hannai Ino in a recirculating aquaculture system

To study the effects of different flow velocities on growth, metabolism and nitrogen (N) and phosphorus (P) budget of Haliotis discus hannai Ino in a recirculating aquaculture system, abalones (shell length: 45.71 ± 3.09 mm, body weight: 8.62 ± 0.75 g) were cultured at three different flow velocities with four replicates each: high (400 L/hr), medium (300 L/hr) and low (200 L/hr). At the end of the 70 days experiment, the survival rate, food intake and P utilization rate of abalones in the 200 L/hr group were significantly lower than those in any other group (p < .05), whereas the total ammonia nitrogen and nitrite nitrogen concentrations in the water were significantly higher than those in any other group (p < .05). The body weight specific growth rate, food conversion efficiency, abalone‐harvested N and P outputs and N utilization rate were ranked as follows: 300 > 400 > 200 L/hr (p < .05). In the 300 L/hr group, the activities of hexokinase, pyruvate kinase and lactate dehydrogenase were significantly lower than those in the 400 L/hr group, whereas the activity of succinate dehydrogenase was significantly higher than that in the other two groups (p < .05). Aerobic metabolism was the main source of energy acquisition for abalones in the 300 L/hr group. In the 400 L/hr group, the expression levels of manganese superoxide dismutase and thioredoxin peroxidase significantly increased from Day 35 to Day 70, but they still were significantly lower than the values in the 200 L/hr group (p < .05). In the 200 L/hr group, the expression levels of catalase and heat shock protein 70 were significantly higher than those in any other group, and they significantly increased from Day 35 to Day 70 (p < .05). These results indicate that maintaining flow velocity at 300 L/hr will minimize oxidative damage due to deterioration of water quality, reduce the energy consumption required for organisms to resist the impact of water flow, improve the N and P utilization rates of the recirculating aquaculture system, and reduce the cost of culturing abalones.