RESEARCH ON THE SWIMMING PERFORMANCE OF JUVENILE SCHIZOTHORAX FISH IN THE YARLUNG ZANGBO RIVER BASIN

The design of fish passage facilities in hydropower projects primarily relies on the swimming ability parameters of target fish species. This study investigated interspecific differences in the individual swimming capacities of juvenile fish from five Schizothorax species in the Yarlung Zangbo River basin, aiming to provide a scientific basis for fishway design and ecological conservation. The subjects comprised juveniles of five species: Schizothorax oconnori, S. macropogon, S. waltoni, Schizopygopsis younghusbandi, and Oxygymnocypris stewartii. The mean body lengths of experimental fish were (9.2±0.8), (3.1±0.1), (8.3±0.8), (5.8±0.9), and (5.4±0.6) cm, respectively. Using an incremental velocity test, the induced flow velocity (Uind), critical swimming speed (Ucrit), and burst swimming speed (Uburst) of the five species were measured. Results revealed that the mean $U^{\mathrm{a}}_{\mathrm{ind}} $ varied between 2.3 and 6.7 cm/s, while the mean $U^{\mathrm{r}}_{\mathrm{ind}} $ varied between 0.4 and 0.8 BL/s. The mean $U^{\mathrm{a}}_{\mathrm{crit}} $ varied between 31.1 and 60.8 cm/s, and the mean $U^{\mathrm{r}}_{\mathrm{crit}} $ ranged from 6.3 to 10.4 BL/s. The mean $U^{\mathrm{a}}_{\mathrm{burst}} $ varied between 39.7 and 88.1 cm/s, with the mean relative $U^{\mathrm{r}}_{\mathrm{burst}} $ varied between 9.7 and 14.6 BL/s. One-way ANOVA and bivariate correlation analysis (body length & swimming capacity metrics) demonstrated significant differences were observed in the swimming performance among the five studied Schizothoracinae fish species at juvenile stages. Schizothorax oconnori and Schizothorax waltoni exhibited higher response flow velocities, whereas Oxygymnocypris stewartii and Schizopygopsis younghusbandi demonstrated advantages in burst swimming speed. This difference is primarily reflected in their adaptation strategies to torrential and slow-flow habitats. Within the body length range studied, body size was found to influence certain performance metrics. The results provide crucial data support for understanding the swimming capabilities of Schizothoracine fish and for the design effective fishways in the Yarlung Zangbo River basin, revealing interspecific differences in individual swimming performance and offering to scientifically informed ecological conservation.