This study aims to investigate the differences in hypoxia tolerance and coping strategies between two freshwater fish species inhabiting two distinct habitats, and to preliminarily verify the applicability of the regulation index (RI) and accumulated oxygen deficit (AOD) in characterizing the hypoxia tolerance of freshwater fish species. Pseudorasbora parva from lentic habitats and Acrossocheilus fasciatus from lotic habitats were used as experimental animals. Through progressive hypoxia experiments, the oxygen partial pressure at loss of equilibrium ( P LOE) was measured for both fish species, and the RI and AOD were calculated based on the fitted curves of metabolic rate versus oxygen partial pressure. The results show that the P LOE of P. parva is lower than that of A. fasciatus , and the difference between the two species is statistically significant( p <0.05), while RI and AOD are higher than those of A. fasciatus, and the difference between the two species is statistically significant( p <0.05). Furthermore, P LOE in P. parva shows a statistically significant negative relationship with RI( p <0.05), but no statistically significant relationship with AOD. In A. fasciatus, P LOE shows no statistically significant relationships with either RI or AOD. These findings suggest that P. parva exhibits stronger hypoxia tolerance than A. fasciatus , which may be related to its greater metabolic regulation capacity and higher potential for anaerobic metabolism. In addition, RI and AOD effectively distinguish interspecific differences in hypoxia tolerance between the two fish species, suggesting that these two indicators are suitable for characterizing hypoxia tolerance in these two fish species.