Effects of flow velocity on growth, food intake, body composition, and related gene expression of Haliotis discus hannai Ino

This study investigated the effects of different flow velocities in a circulating aquaculture system on growth, food intake, and related gene expression of the abalone Haliotis discus hannai Ino. Abalones (shell length: 41.39 ± 2.85 mm, body weight: 8.19 ± 0.66 g) were cultured at three flow velocities; high-velocity (400 L/h), medium-velocity (300 L/h), and low-velocity (200 L/h) during the course of the experiment. Four repeats of each flow velocity were conducted over an experimental cycle of 90 days. Results showed that the survival and specific growth rate of abalones in the 200 L/h group were significantly lower than in any other group at the end of the experiment, while total ammonia nitrogen and NO2‑N concentration in the water was significantly higher than that in any other group (P < 0.05). Food intake, food conversion efficiency, protein content, pepsin, and α-amylase activity of abalones in the 300 L/h group were significantly higher than in the 200 and 400 L/h groups (P < 0.05), but there was no significant difference identified between 200 and 400 L/h groups (P > 0.05). Although no significant difference was identified between 300 and 400 L/h groups with respect to cellulase activity or the expression levels of Hdaly, both were significantly higher than in the 200 L/h group (P < 0.05). In the 400 L/h group, hexokinase and pyruvate kinase activity, and lactic acid content were significantly higher compared with in the 300 L/h group (P < 0.05). The ash and fat contents of abalones in the 200 L/h group were significantly lower than in any other group, but moisture content was significantly higher (P < 0.05). At Day 90, the expression levels of Hdamyl, Hdlam, and Hdcel in the 300 L/h group were significantly higher than in any other group (P < 0.05), and compared with Day 45, the expression levels of were Hdamyl significantly increased (P < 0.05). Although no significant difference was identified between 200 and 400 L/h groups with respect to the expression levels of Mn-SOD and CAT, both were significantly higher than those in the 300 L/h group (P < 0.05). Therefore, control of flow velocity at 300 L/h will not only stimulate the food intake and growth of abalones, but also reduce energy consumption to resist against water flow impact and avoid oxidative damage due to water quality deterioration. This will be beneficial for abalone health and will improve aquaculture production.