Abstract: Qinling lenok Brachymystax tsinlingensis, a threatened salmonid species endemic to the Qinling Mountain Range, is a second-class state-protected wild animal in China Red Data Book of Endangered Animals. This species is landlocked and adapted to cold-water environments, specifically occurring in Qinling streams together with Phoxinus lagowskii. In order to explore the interspecific differences in swimming performance and metabolic characteristics between B. tsinlingensis and their main prey fish P. lagowskii, the anaerobic exercise ability (i.e., constant acceleration test speed, U_cat), aerobic exercise ability (i.e., gait transition speed, U_gait and critical swimming speed, U_crit), resting metabolic rate (RMR), maximum metabolic rate (MMR), aerobic metabolic scope (MS), and the energetic cost of transport (COT) of wild populations of both species were measured using a Brett-type swimming tunnel respirometer. The results showed that: (1) the U_crit and U_cat of B. tsinlingensis were higher than those of P. lagowskii (P<0.05), but there was no significant difference in the relative swimming abilities (including rU_gait, rU_crit and rU_cat) between the two species (P>0.05). (2) The RMR, MMR, and MS of B. tsinlingensis were significantly higher than those of P. lagowskii (P<0.05). Morover, both the oxygen consumption rate and COT at a specific swimming speed were higher than those of P. lagowskii. (3) The U_crit of B. tsinlingensis showed a significant positive correlation or a trend of positive correlation with MS and MMR, while the U_crit of P. lagowskii was not correlated with either MS or MMR (P>0.05). The results suggest that the relative swimming performance of B. tsinlingensis is similar to that of P. lagowskii, whereas the swimming efficiency of B. tsinlingensis is lower. On the other hand, B. tsinlingensis have greater metabolic potential, which is an important driving force for supporting their swimming performance. These findings are expected to provide a theoretical reference for studying the conservation physiology of B. tsinlingensis and understanding the dynamics of interspecific relationships in Qinling stream ecosystems.