Abstract: The aim of this study is to investigate the effects of different water velocities on the growth performance, antioxidant capacity, energy metabolism and tissue structure of Micropterus salmoides kept in an in-pond recirculation aquaculture (IPRA) system. 192 well-fed, healthy and uniformly sized largemouth bass average weight: (8.13±0.82) g were randomly assigned to 4 simulation tanks with 3 duplicates containing 16 fish each. The experiment was set up with a control group (a stagnant water group) and three water flow rate groups, namely, a low flow rate group (0.2 m/s), a medium flow rate group (0.4 m/s) and a high flow rate group (0.6 m/s), respectively, with a culture period of 154 days. The results were as follows: (1) WGR and SGR of largemouth bass in the medium flow rate group were significantly higher than those of the other three groups (P<0.05), while the SGR of the high flow rate group was significantly lower than that of the other three treatment groups. The CF was significantly lower in the medium and high flow rate groups than that in the stagnant water and low flow rate groups. The visceral adiposity index (VAI) of largemouth bass decreased significantly with the increasing of flow rate (P<0.05). (2) The crude protein levels of muscle were significantly higher in the medium flow rate group than that in the other three groups. The crude fat content of muscle was significantly higher in the stagnant water and low flow rate groups than that in the medium and high low rate groups. The amount of crude fat in the specimens decreased significantly with an increased flow rate of water (P<0.05). (3) Serum triglycerides and the total amount of cholesterol in the specimens were significantly lower in the medium and high flow rate groups than that in the stagnant water and low flow rate groups (P<0.05). The concentration of free fatty acids and total amount of protein were significantly lower in the high flow rate group than that in the other three groups (P<0.05). (4) SOD and CAT increased with the increasing of the water flow rate, with the highest SOD level in the livers of the specimens in the medium flow rate group and there was a significantly higher concentration of serum CAT in the high flow rate group than the other three groups (P<0.05). Serum and liver tissue MDA levels were significantly lower in the medium flow rate group than that in the other three groups (P<0.05). The AOC of serum and liver tissues were significantly higher in the medium flow rate group than that in the other three groups (P<0.05). (5) LPS activity increased significantly in the specimens tested with an increased flow rate (P<0.05). AMS and PTS activities were the highest in the medium flow rate group. Hepatic LPS activity was the highest in the medium flow rate group, which was significantly higher than that in the stagnant water and low flow rate groups (P<0.05). PTS activity was significantly higher in the medium and high flow rate groups than that in the low flow rate groups. GDH increased significantly with the increased flow rate in both the muscles and liver (P<0.05). (6) The diameter of muscle fibres in the low flow rate group was significantly higher than that in the other three treatment groups (P<0.05). The density of muscle fibres increased significantly with an increase of water velocity. The medium flow group improved the tissue structure, while the high flow group caused some damage to their liver cells. In conclusion, the medium flow rate group with a flow rate of 0.4 m/s can promote the growth of largemouth bass, boost the immune systems, improve the functioning of their metabolisms, increase the crude protein content and inhibit fat deposition, and should be used as the optimal water flow rate for IPRA.