Abstract: Opsariichthys bidens, an important economic fish with a small body size, widely exists in the Yangtze River Basin. The swimming endurance, critical swimming speed and sprint swimming speed are important parameters of fish swimming ability, and closely related to the fishway design. Based on the experiments performed in a swimming tunnel, a total of 215 fish (8.78-16.81 cm, TL) were tested, including 128 fish for the test on swimming endurance, 31 fish on critical swimming speed and 56 fish on the sprint swimming speed. Fixed velocity tests revealed that over 84% of the fatigue time was distributed in the two ranges: either <10 min or >200 min. The relationship between fatigue time (E), swimming velocity (V) and total length (TL) could be fitted as lgE=1.603-0.025V+0.146TL (R²=0.562, P<0.001). According to the fitting equation, the relationship between the maximum length of the fishway and the maximum allowable flow can be predicted, and the combined conditions can be tested on the fishway length and maximum water velocity that are suitable for passing Opsariichthys bidens (TL=9.60 cm) at 21.4 °C. Critical swimming speed value of the experimental fish was distributed in 61.07-120.03 cm·s^-1 (the relative critical swimming speed: 6.57-12.65 BL·s^-1), and the range of sprint swimming speed was 65.03-155.07 cm·s^-1 (the relative sprint swimming speed: 5.31-17.95 BL·s^-1). It was concluded that with regard to the sprint swimming speed, 78% of the experimental fish was greater than 1 m·s^-1, and the average sprint swimming speed was about 1.23 times as fast as the average critical swimming speed. The results can provide basis for the hydraulic parameters of the fishway design.

Key words: water and sediment transport, arid region., land use, NDVI, climate change, upper Yellow River