Swimming performance is considered a critical factor in determining the survival of many fish species under natural conditions. Flume experimentation, which is visible, measurable, and repeatable for the adjustment and control of environmental factors, is a basic and effective method for the study of swimming performance and behavior in fish. However, many current studies of fish behavior have focused solely on the process of adaptation, while other influencing factors such as temperature, light, dissolved oxygen, velocity, and time have been generally ignored. In addition, maximal sustained swimming time and maximal sustained swimming speed are accepted as key indicators for determining swimming performance in fish. Swimming performance is assessed by determining the maximum sustained swimming performance at a given time and constant speed, and maximal sustained swimming speed is used as the base-line reference when fish become fatigued. The lenok, Brachymystax lenok (Pallas), is one of the rare and valuable salmonid species found in the northeast of China. In recent years, the biology, ecology, reproduction success, disease prevention, and culture techniques of this species have been extensively studied and reported. However, to the best of our knowledge, there have been very few studies on the behavioral ecology of this species. In this report, the effects of acclimation time, acclimation flow velocity, acceleration time, and tested flow velocity on the sustained swimming time of juvenile lenok were investigated at a water temperature of 16.0 ± 0.2 ℃ and dissolved oxygen level of 8 mg/L. The observed results served as reference data on the ethology, kinematics, energetics, and behavioral ecology of this species. Uniform experimental design was used with four factors and eight levels being applied to all tests. The results revealed that the maximal acclimation flow velocity (AFV_max) should be limited to 1.0-1.5 (body lengths) BL/s, with a corresponding optimum acclimation time (AT) of 1 h. Under reasonable conditions (AFV_max≤ 1.0-1.5 BL/s, AT ≤ 1 h), the influence of acclimation flow velocity and acclimation time on sustainable swimming performance was negligible. Acceleration time significantly affected sustained swimming time under stronger flow velocities (> 0.5 m/s) (P < 0.05). Although a longer time period may be favorable in allowing fish to adjust to a new environment, an acclimation time of 1-2 h is recommended; screening for a suitable acclimation time should be performed before trials. It is recommended that the tested flow velocity be limited to 3-4 BL/s to avoid the maximum swimming tolerance range. Sustained swimming time was significantly affected by the tested flow velocities: sustained swimming time decreased significantly with an increase in flow velocity (P < 0.05). The energy loss in fish was also affected by tested flow velocity, acceleration time, and acclimation time. Under the maximal tested flow velocity (> 0.5 m/s), the maximal acclimation time and the acceleration time should be limited to 60 and 4 min, respectively. In conclusion, this study provides a scientific baseline for the behavioral ecology, kinematic theory, and energetics of B. lenok, which will prove valuable for the design and construction of fish-pass facilities.