The in-pond raceway system (IPRS) combines the sustainable development of environmental protection and high yields. Compared with traditional pond culture, the IPRS can improve the survival rate, muscle nutrition, liver biological function, and antioxidant capacity of largemouth bass (). Stocking density is an important environmental factor in the in-pond raceway system, but the high densitie can cause stress responses in fish, which have negative impacts on growth, behavior, and physiology. Therefore, a suitable stocking density for largemouth bass () in a recirculating aquaculture system needs to be identified. A 120-day feeding experiment was performed to study the effects of stocking densities on the antioxidant state, digestive enzymes, tissue structure, and the gene expressions of in largemouth bass (average initial body weight 4.50±0.23 g) reared in in-pond raceway culture systems. The fish were divided into three density groups (SD1, 0.2 kg/m³; SD2, 0.4 kg/m³; and SD3, 0.6 kg/m³). Each density was tested in triplicate. The relative indicators in the liver and intestine were measured, and the histological structures of the liver and intestine were observed at days 30, 60, 90, and 120. The results showed that the final densities at the end of the experiment were 5.64 kg/m³ (SD1), 8.79 kg/m³ (SD2), and 11.21 kg/m³ (SD3). There were no significant difference in liver SOD and CAT activity among the treatments on days 30, 60, and 90 (>0.05). However, the fish reared in the SD1 group had significantly higher values than those reared in the SD3 group on day 120 (>0.05). There were no significant differences in the MDA contents of the livers before 60 d (>0.05), but fish reared in the SD3 group had significantly higher values than those reared in the SD1 group on days 90 and 120 (>0.05). The amylase and lipase activities in the intestines of the fish reared at the three groups were not significantly different (HSP70 and P>0.05).The expression of in the livers of the fish from SD3 was significantly higher than those from the SD1 and SD2 groups at 90 d and 120 d ( mRNA in the livers of the fish in SD1 was significantly higher than that in SD3 at 90-120 d (>0.05). The tissue section observations showed that the liver and intestinal tissues of the three density groups were normal and not seriously damaged, whereas the stress caused by the high stocking density led to a slight increase in vacuoles among the liver tissues and a decrease in the size and number of intestinal goblet cells at the end of the experiment. The results showed that the stress caused by the high stocking density inhibited the antioxidant capacity of largemouth bass and affected the expression of the genes in the liver. It also had a slight effect on liver and intestinal structure. In conclusion, the stocking density affected the physiological status of largemouth bass and inhibited the antioxidant and immune functions of the fish. Moreover, the high-density stress caused slight damage to the liver and intestinal tissues under the conditions of this experiment. In summary, the largemouth bass reared in the 0.2 kg/m³ density group had the best physiological status. Overall, the results suggest that largemouth bass can be reared at stocking densities of 0.2−0.4 kg/m³ in an IPRS.