Abstract:The increasing velocity method was adopted to test critical swimming speed of Gymnocypris przewalskii using a wild migratory group and cultured groups of the ages of 1 and 2 years old, and then the fixed velocity method was used to test the swimming endurance of G. przewalskii. Finally, we simulated a three-stage fish ladder and calculated and analyzed the efficiency of fish passing the ladder. The results showed that: The absolute critical swimming speed (Ucrit) of the wild migration group (35.73±6.56) cm/s was significantly lower than that of the 2-year-old cultured group (57.77± 10.25) cm/s (P<0.01), but there was no significant difference between the wild migration group and the 1-year-old cultured group (31.66±9.97) cm/s (P>0.05). The relative critical swimming speed (U′crit) of the 1-year-old cultured group (3.25±1.42) BL/s, the 2-year-old cultured group (2.71±0.61) BL/s and the wild migratory group (1.71±0.35) BL/s significantly decreased with the increase of body length and age (P<0.01). The U′crit of males in the wild migratory group (1.96±0.27) BL/s was significantly higher than that of the female (1.54±0.31) BL/s (P<0.01), while there were no significant difference between the sexes in the 1-year-old and 2-year-old cultured groups (P>0.05). The duration of swimming in wild G. przewalskii was very short at a high flow rate of 100 cm/s (27.67±5.67) s, and there was a significant negative correlation between the duration of swimming and the flow velocity (P<0.01). The passing rate of wild G. przewalskii at three levels of the fish ladder was significantly different (P<0.01), and the lowest pass rate was only 36%. This study shows that G. przewalskii, a typical cold-water fish in high altitude and high salinity environments, has a relatively weak swimming ability and is likely to be affected by dams and other obstacles during their migration. The results of this study could provide basic data for the design and optimization of fish ladders and the protection of the migratory populations of G. przewalskii.
