Here, we aimed to determine the effects of water temperature and flow velocity on the respiratory metabolism and behavior of one- and two-year-old Phoxinus lagowskii Dybowski by using experimental ecological methods. The results showed that yearling and two-year-old P. lagowskii did not feed and showed slow growth at 4℃. With an increase in water temperature, fish feeding and growth improved. However, at 28℃, the feeding activities of P. lagowskii reduced, and significant weight loss was noted; the fish began to die after 7 d, and the death rate increased gradually. The oxygen consumption rate increased at a flow velocity of 16 cm/s and 18 cm/s, as well as with increasing temperature from 4℃ to 28℃, showing a typical exponential growth trend. The equation was Y=ae^bx (R² > 0.90). Regardless of the temperature changes, yearling and two-year-old P. lagowskii showed no significant differences in their state, i.e., the number of times they wagged their tail, lied prone at the bottom, and had a disorganized head position, at a flow rate of 8 cm/s and 10 cm/s. In contrast, at the flow rate of 16 cm/s and 18 cm/s, the oxygen consumption rate declined with an increase in temperature from 4℃ to 28 ℃. The oxygen consumption rate increased with an increase in flow velocity from 8 cm/s to 18 cm/s at temperatures below 20℃ in yearling fish or below 24℃ in two-year-old fish. However, at the flow velocity of 16 cm/s, the oxygen consumption rate of yearling fish reached the highest level at temperatures of 24-28℃, and that of two-year-fish reached the highest level at 28℃, and decreased thereafter. When the flow velocity was 18 cm/s, the tail wagging speed reached the highest level, and yearling fish came closer to the net and stopped swimming after 30 min, whereas two-year-old fish came closer to the net after 1 h. The optimum temperature for yearling fish fluctuated within the optimum breeding flow velocity of 12-16 cm/s. The minimum area of Q₁₀ was in the range of 16-24℃ when the flow velocity was 12 cm/s and 14 cm/s, but it was in the range of 16-20℃ and 24-28℃ when the flow velocity was 16 cm/s. According to the line graph for flow velocity vs. oxygen consumption rate, the maximum oxygen consumption rate was recorded at 24℃; the metabolic activity of the fish has reached its limit at this temperature. A low Q₁₀ value was recorded at 24-28℃ when the flow velocity was 16 cm/s, but this temperature was not suitable for farming yearling fish. Moreover, the lowest Q₁₀ value for two-year-old fish was recorded at 8-24℃ at a flow velocity of 12-16 cm/s. The temperature range for the lowest Q₁₀ value for two-year-old fish was significantly wider than that for yearling fish. These results suggested that the respiratory metabolism of P. lagowskii was influenced by the size of the fish, flow velocity, temperature, and other factors. Large two-year-old fish have greater ability to adapt to the changing aquatic environment and a lower oxygen consumption rate than yearling fish. The optimal conditions for yearling P. lagowskii were a flow velocity of 12-14 cm/s and water temperature of 16-24℃. On the other hand, the optimal flow velocity and water temperature were 12-16 cm/s and 8-24℃, respectively, for two-year-old P. lagowskii.